Merge remote-tracking branch 'upstream/master' into features/DevTools/PropertyType

build/MicroCom.targets

@@ -15,7 +15,8 @@
           Inputs="@(AvnComIdl);$(MSBuildThisFileDirectory)../src/tools/MicroComGenerator/**/*.cs"
           Outputs="%(AvnComIdl.OutputFile)">
     <Message Importance="high" Text="Generating file %(AvnComIdl.OutputFile) from @(AvnComIdl)" />
-    <Exec Command="dotnet $(MSBuildThisFileDirectory)../src/tools/MicroComGenerator/bin/$(Configuration)/netcoreapp3.1/MicroComGenerator.dll -i @(AvnComIdl) --cs %(AvnComIdl.OutputFile)" LogStandardErrorAsError="true" />
+    <Exec Command="dotnet &quot;$(MSBuildThisFileDirectory)../src/tools/MicroComGenerator/bin/$(Configuration)/netcoreapp3.1/MicroComGenerator.dll&quot; -i @(AvnComIdl) --cs %(AvnComIdl.OutputFile)" 
+          LogStandardErrorAsError="true" />
     <ItemGroup>
       <!-- Remove and re-add generated file, this is needed for the clean build -->
       <Compile Remove="%(AvnComIdl.OutputFile)"/>

native/Avalonia.Native/src/OSX/KeyTransform.mm

@@ -222,6 +222,7 @@ std::map<int, const char*> s_QwertyKeyMap =
     { 45, "n" },
     { 46, "m" },
     { 47, "." },
+    { 48, "\t" },
     { 49, " " },
     { 50, "`" },
     { 51, "" },

native/Avalonia.Native/src/OSX/window.h

@@ -10,6 +10,8 @@ class WindowBaseImpl;
 -(void) setSwRenderedFrame: (AvnFramebuffer* _Nonnull) fb dispose: (IUnknown* _Nonnull) dispose;
 -(void) onClosed;
 -(AvnPixelSize) getPixelSize;
+-(AvnPlatformResizeReason) getResizeReason;
+-(void) setResizeReason:(AvnPlatformResizeReason)reason;
 @end
 
 @interface AutoFitContentView : NSView
@@ -34,6 +36,7 @@ class WindowBaseImpl;
 -(double) getScaling;
 -(double) getExtendedTitleBarHeight;
 -(void) setIsExtended:(bool)value;
+-(bool) isDialog;
 @end
 
 struct INSWindowHolder
@@ -50,4 +53,23 @@ struct IWindowStateChanged
     virtual AvnWindowState WindowState () = 0;
 };
 
+class ResizeScope
+{
+public:
+    ResizeScope(AvnView* _Nonnull view, AvnPlatformResizeReason reason)
+    {
+        _view = view;
+        _restore = [view getResizeReason];
+        [view setResizeReason:reason];
+    }
+    
+    ~ResizeScope()
+    {
+        [_view setResizeReason:_restore];
+    }
+private:
+    AvnView* _Nonnull _view;
+    AvnPlatformResizeReason _restore;
+};
+
 #endif /* window_h */

native/Avalonia.Native/src/OSX/window.mm

@@ -52,6 +52,7 @@ public:
         [Window setBackingType:NSBackingStoreBuffered];
         
         [Window setOpaque:false];
+        [Window setContentView: StandardContainer];
     }
     
     virtual HRESULT ObtainNSWindowHandle(void** ret) override
@@ -115,7 +116,7 @@ public:
         return Window;
     }
     
-    virtual HRESULT Show(bool activate) override
+    virtual HRESULT Show(bool activate, bool isDialog) override
     {
         START_COM_CALL;
         
@@ -124,7 +125,6 @@ public:
             SetPosition(lastPositionSet);
             UpdateStyle();
             
-            [Window setContentView: StandardContainer];
             [Window setTitle:_lastTitle];
             
             if(ShouldTakeFocusOnShow() && activate)
@@ -277,7 +277,7 @@ public:
         }
     }
     
-    virtual HRESULT Resize(double x, double y) override
+    virtual HRESULT Resize(double x, double y, AvnPlatformResizeReason reason) override
     {
         if(_inResize)
         {
@@ -287,6 +287,7 @@ public:
         _inResize = true;
         
         START_COM_CALL;
+        auto resizeBlock = ResizeScope(View, reason);
         
         @autoreleasepool
         {
@@ -317,7 +318,7 @@ public:
             {
                 if(!_shown)
                 {
-                    BaseEvents->Resized(AvnSize{x,y});
+                    BaseEvents->Resized(AvnSize{x,y}, reason);
                 }
                 
                 [Window setContentSize:NSSize{x, y}];
@@ -577,6 +578,11 @@ public:
         return S_OK;
     }
 
+    virtual bool IsDialog()
+    {
+        return false;
+    }
+    
 protected:
     virtual NSWindowStyleMask GetStyle()
     {
@@ -607,6 +613,7 @@ private:
     NSRect _preZoomSize;
     bool _transitioningWindowState;
     bool _isClientAreaExtended;
+    bool _isDialog;
     AvnExtendClientAreaChromeHints _extendClientHints;
     
     FORWARD_IUNKNOWN()
@@ -667,13 +674,14 @@ private:
         }
     }
     
-    virtual HRESULT Show (bool activate) override
+    virtual HRESULT Show (bool activate, bool isDialog) override
     {
         START_COM_CALL;
         
         @autoreleasepool
         {
-            WindowBaseImpl::Show(activate);
+            _isDialog = isDialog;
+            WindowBaseImpl::Show(activate, isDialog);
             
             HideOrShowTrafficLights();
             
@@ -705,6 +713,12 @@ private:
             if(cparent == nullptr)
                 return E_INVALIDARG;
             
+            // If one tries to show a child window with a minimized parent window, then the parent window will be
+            // restored but MacOS isn't kind enough to *tell* us that, so the window will be left in a non-interactive
+            // state. Detect this and explicitly restore the parent window ourselves to avoid this situation.
+            if (cparent->WindowState() == Minimized)
+                cparent->SetWindowState(Normal);
+            
             [cparent->Window addChildWindow:Window ordered:NSWindowAbove];
             
             UpdateStyle();
@@ -1196,6 +1210,7 @@ private:
                 }
                 
                 _actualWindowState = _lastWindowState;
+                WindowEvents->WindowStateChanged(_actualWindowState);
             }
             
             
@@ -1213,6 +1228,11 @@ private:
         }
     }
     
+    virtual bool IsDialog() override
+    {
+        return _isDialog;
+    }
+    
 protected:
     virtual NSWindowStyleMask GetStyle() override
     {
@@ -1373,6 +1393,7 @@ NSArray* AllLoopModes = [NSArray arrayWithObjects: NSDefaultRunLoopMode, NSEvent
     bool _lastKeyHandled;
     AvnPixelSize _lastPixelSize;
     NSObject<IRenderTarget>* _renderTarget;
+    AvnPlatformResizeReason _resizeReason;
 }
 
 - (void)onClosed
@@ -1484,7 +1505,8 @@ NSArray* AllLoopModes = [NSArray arrayWithObjects: NSDefaultRunLoopMode, NSEvent
         _lastPixelSize.Height = (int)fsize.height;
         [self updateRenderTarget];
     
-        _parent->BaseEvents->Resized(AvnSize{newSize.width, newSize.height});
+        auto reason = [self inLiveResize] ? ResizeUser : _resizeReason;
+        _parent->BaseEvents->Resized(AvnSize{newSize.width, newSize.height}, reason);
     }
 }
 
@@ -1983,6 +2005,16 @@ NSArray* AllLoopModes = [NSArray arrayWithObjects: NSDefaultRunLoopMode, NSEvent
     
 }
 
+- (AvnPlatformResizeReason)getResizeReason
+{
+    return _resizeReason;
+}
+
+- (void)setResizeReason:(AvnPlatformResizeReason)reason
+{
+    _resizeReason = reason;
+}
+
 @end
 
 
@@ -2002,6 +2034,11 @@ NSArray* AllLoopModes = [NSArray arrayWithObjects: NSDefaultRunLoopMode, NSEvent
     _isExtended = value;
 }
 
+-(bool) isDialog
+{
+    return _parent->IsDialog();
+}
+
 -(double) getScaling
 {
     return _lastScaling;
@@ -2180,7 +2217,22 @@ NSArray* AllLoopModes = [NSArray arrayWithObjects: NSDefaultRunLoopMode, NSEvent
 
 -(BOOL)canBecomeKeyWindow
 {
-    return _canBecomeKeyAndMain;
+    if (_canBecomeKeyAndMain)
+    {
+        // If the window has a child window being shown as a dialog then don't allow it to become the key window.
+        for(NSWindow* uch in [self childWindows])
+        {
+            auto ch = objc_cast<AvnWindow>(uch);
+            if(ch == nil)
+                continue;
+            if (ch.isDialog)
+                return false;
+        }
+        
+        return true;
+    }
+    
+    return false;
 }
 
 -(BOOL)canBecomeMainWindow
@@ -2188,22 +2240,6 @@ NSArray* AllLoopModes = [NSArray arrayWithObjects: NSDefaultRunLoopMode, NSEvent
     return _canBecomeKeyAndMain;
 }
 
--(bool) activateAppropriateChild: (bool)activating
-{
-    for(NSWindow* uch in [self childWindows])
-    {
-        auto ch = objc_cast<AvnWindow>(uch);
-        if(ch == nil)
-            continue;
-        [ch activateAppropriateChild:false];
-        return FALSE;
-    }
-    
-    if(!activating)
-        [self makeKeyAndOrderFront:self];
-    return TRUE;
-}
-
 -(bool)shouldTryToHandleEvents
 {
     return _isEnabled;
@@ -2214,26 +2250,15 @@ NSArray* AllLoopModes = [NSArray arrayWithObjects: NSDefaultRunLoopMode, NSEvent
     _isEnabled = enable;
 }
 
--(void)makeKeyWindow
-{
-    if([self activateAppropriateChild: true])
-    {
-        [super makeKeyWindow];
-    }
-}
-
 -(void)becomeKeyWindow
 {
     [self showWindowMenuWithAppMenu];
     
-    if([self activateAppropriateChild: true])
+    if(_parent != nullptr)
     {
-        if(_parent != nullptr)
-        {
-            _parent->BaseEvents->Activated();
-        }
+        _parent->BaseEvents->Activated();
     }
-    
+
     [super becomeKeyWindow];
 }
 
@@ -2243,7 +2268,6 @@ NSArray* AllLoopModes = [NSArray arrayWithObjects: NSDefaultRunLoopMode, NSEvent
     if(parent != nil)
     {
         [parent removeChildWindow:self];
-        [parent activateAppropriateChild: false];
     }
 }
 
@@ -2378,7 +2402,7 @@ protected:
         return NSWindowStyleMaskBorderless;
     }
     
-    virtual HRESULT Resize(double x, double y) override
+    virtual HRESULT Resize(double x, double y, AvnPlatformResizeReason reason) override
     {
         START_COM_CALL;
         

samples/ControlCatalog/Pages/DataGridPage.xaml

@@ -28,7 +28,7 @@
                     DockPanel.Dock="Top"/>
           <DataGrid Name="dataGrid1" Margin="12" CanUserResizeColumns="True" CanUserReorderColumns="True" CanUserSortColumns="True" HeadersVisibility="All">
             <DataGrid.Columns>
-              <DataGridTextColumn Header="Country" Binding="{Binding Name}" Width="6*" />
+              <DataGridTextColumn Header="Country" Binding="{Binding Name}" Width="6*" MinWidth="400"  />
               <!-- CompiledBinding example of usage. -->
               <DataGridTextColumn Header="Region" Binding="{CompiledBinding Region}" Width="4*" x:DataType="local:Country" />
               <DataGridTextColumn Header="Population" Binding="{Binding Population}" Width="3*" />

samples/ControlCatalog/SideBar.xaml

@@ -16,7 +16,6 @@
         <Setter Property="Template">
             <ControlTemplate>
                 <Border 
-                    Margin="{TemplateBinding Margin}"
                     BorderBrush="{TemplateBinding BorderBrush}"
                     BorderThickness="{TemplateBinding BorderThickness}">
                     <DockPanel>

samples/RenderDemo/SideBar.xaml

@@ -7,7 +7,6 @@
     <Setter Property="Template">
       <ControlTemplate>
         <Border
-            Margin="{TemplateBinding Margin}"
             BorderBrush="{TemplateBinding BorderBrush}"
             BorderThickness="{TemplateBinding BorderThickness}">
           <DockPanel>

src/Android/Avalonia.Android/Platform/SkiaPlatform/TopLevelImpl.cs

@@ -67,7 +67,7 @@ namespace Avalonia.Android.Platform.SkiaPlatform
 
         public Action<Rect> Paint { get; set; }
 
-        public Action<Size> Resized { get; set; }
+        public Action<Size, PlatformResizeReason> Resized { get; set; }
 
         public Action<double> ScalingChanged { get; set; }
 
@@ -134,7 +134,7 @@ namespace Avalonia.Android.Platform.SkiaPlatform
 
         protected virtual void OnResized(Size size)
         {
-            Resized?.Invoke(size);
+            Resized?.Invoke(size, PlatformResizeReason.Unspecified);
         }
 
         class ViewImpl : InvalidationAwareSurfaceView, ISurfaceHolderCallback, IInitEditorInfo

src/Avalonia.Base/AvaloniaObject.cs

@@ -861,7 +861,7 @@ namespace Avalonia
         }
 
         /// <summary>
-        /// Logs a mesage if the notification represents a binding error.
+        /// Logs a message if the notification represents a binding error.
         /// </summary>
         /// <param name="property">The property being bound.</param>
         /// <param name="value">The binding notification.</param>

src/Avalonia.Base/AvaloniaProperty.cs

@@ -465,9 +465,9 @@ namespace Avalonia
         /// Uses the visitor pattern to resolve an untyped property to a typed property.
         /// </summary>
         /// <typeparam name="TData">The type of user data passed.</typeparam>
-        /// <param name="vistor">The visitor which will accept the typed property.</param>
+        /// <param name="visitor">The visitor which will accept the typed property.</param>
         /// <param name="data">The user data to pass.</param>
-        public abstract void Accept<TData>(IAvaloniaPropertyVisitor<TData> vistor, ref TData data)
+        public abstract void Accept<TData>(IAvaloniaPropertyVisitor<TData> visitor, ref TData data)
             where TData : struct;
 
         /// <summary>

src/Avalonia.Base/AvaloniaPropertyChangedEventArgs.cs

@@ -58,8 +58,8 @@ namespace Avalonia
         /// <remarks>
         /// This will usually be true, except in
         /// <see cref="AvaloniaObject.OnPropertyChangedCore{T}(AvaloniaPropertyChangedEventArgs{T})"/>
-        /// which recieves notifications for all changes to property values, whether a value with a higher
-        /// priority is present or not. When this property is false, the change that is being signalled
+        /// which receives notifications for all changes to property values, whether a value with a higher
+        /// priority is present or not. When this property is false, the change that is being signaled
         /// has not resulted in a change to the property value on the object.
         /// </remarks>
         public bool IsEffectiveValueChange { get; private set; }

src/Avalonia.Base/Collections/Pooled/PooledList.cs

@@ -1271,7 +1271,7 @@ namespace Avalonia.Collections.Pooled
         /// Reverses the elements in a range of this list. Following a call to this
         /// method, an element in the range given by index and count
         /// which was previously located at index i will now be located at
-        /// index index + (index + count - i - 1).
+        /// index + (index + count - i - 1).
         /// </summary>
         public void Reverse(int index, int count)
         {

src/Avalonia.Base/Data/Converters/BoolConverters.cs

@@ -18,5 +18,11 @@ namespace Avalonia.Data.Converters
         /// </summary>
         public static readonly IMultiValueConverter Or =
             new FuncMultiValueConverter<bool, bool>(x => x.Any(y => y));
+
+        /// <summary>
+        /// A value converter that returns true when input is false and false when input is true.
+        /// </summary>
+        public static readonly IValueConverter Not =
+            new FuncValueConverter<bool, bool>(x => !x);
     }
 }

src/Avalonia.Base/Data/Core/Plugins/IDataValidationPlugin.cs

@@ -20,7 +20,7 @@ namespace Avalonia.Data.Core.Plugins
         /// </summary>
         /// <param name="reference">A weak reference to the object.</param>
         /// <param name="propertyName">The property name.</param>
-        /// <param name="inner">The inner property accessor used to aceess the property.</param>
+        /// <param name="inner">The inner property accessor used to access the property.</param>
         /// <returns>
         /// An <see cref="IPropertyAccessor"/> interface through which future interactions with the 
         /// property will be made.

src/Avalonia.Base/DirectPropertyBase.cs

@@ -13,7 +13,7 @@ namespace Avalonia
     /// <typeparam name="TValue">The type of the property's value.</typeparam>
     /// <remarks>
     /// Whereas <see cref="DirectProperty{TOwner, TValue}"/> is typed on the owner type, this base
-    /// class provides a non-owner-typed interface to a direct poperty.
+    /// class provides a non-owner-typed interface to a direct property.
     /// </remarks>
     public abstract class DirectPropertyBase<TValue> : AvaloniaProperty<TValue>
     {
@@ -123,9 +123,9 @@ namespace Avalonia
         }
 
         /// <inheritdoc/>
-        public override void Accept<TData>(IAvaloniaPropertyVisitor<TData> vistor, ref TData data)
+        public override void Accept<TData>(IAvaloniaPropertyVisitor<TData> visitor, ref TData data)
         {
-            vistor.Visit(this, ref data);
+            visitor.Visit(this, ref data);
         }
 
         /// <inheritdoc/>

src/Avalonia.Base/DirectPropertyMetadata`1.cs

@@ -38,7 +38,7 @@ namespace Avalonia
         /// <remarks>
         /// Data validation is validation performed at the target of a binding, for example in a
         /// view model using the INotifyDataErrorInfo interface. Only certain properties on a
-        /// control (such as a TextBox's Text property) will be interested in recieving data
+        /// control (such as a TextBox's Text property) will be interested in receiving data
         /// validation messages so this feature must be explicitly enabled by setting this flag.
         /// </remarks>
         public bool? EnableDataValidation { get; private set; }

src/Avalonia.Controls.DataGrid/Collections/DataGridCollectionView.cs

@@ -877,7 +877,7 @@ namespace Avalonia.Collections
                         if (!CheckFlag(CollectionViewFlags.IsMoveToPageDeferred))
                         {
                             // if the temporaryGroup was not created yet and is out of sync
-                            // then create it so that we can use it as a refernce while paging.
+                            // then create it so that we can use it as a reference while paging.
                             if (IsGrouping && _temporaryGroup.ItemCount != InternalList.Count)
                             {
                                 PrepareTemporaryGroups();
@@ -889,7 +889,7 @@ namespace Avalonia.Collections
                     else if (IsGrouping)
                     {
                         // if the temporaryGroup was not created yet and is out of sync
-                        // then create it so that we can use it as a refernce while paging.
+                        // then create it so that we can use it as a reference while paging.
                         if (_temporaryGroup.ItemCount != InternalList.Count)
                         {
                             // update the groups that get created for the
@@ -1951,7 +1951,7 @@ namespace Avalonia.Collections
             EnsureCollectionInSync();
             VerifyRefreshNotDeferred();
 
-            // for indicies larger than the count
+            // for indices larger than the count
             if (index >= Count || index < 0)
             {
                 throw new ArgumentOutOfRangeException("index");
@@ -3800,7 +3800,7 @@ namespace Avalonia.Collections
         /// </summary>
         /// <remarks>
         /// This method can be called from a constructor - it does not call
-        /// any virtuals.  The 'count' parameter is substitute for the real Count,
+        /// any virtuals. The 'count' parameter is substitute for the real Count,
         /// used only when newItem is null.
         /// In that case, this method sets IsCurrentAfterLast to true if and only
         /// if newPosition >= count.  This distinguishes between a null belonging

src/Avalonia.Controls.DataGrid/DataGrid.cs

@@ -25,6 +25,7 @@ using System.ComponentModel.DataAnnotations;
 using Avalonia.Controls.Utils;
 using Avalonia.Layout;
 using Avalonia.Controls.Metadata;
+using Avalonia.Input.GestureRecognizers;
 
 namespace Avalonia.Controls
 {
@@ -67,7 +68,7 @@ namespace Avalonia.Controls
         private const double DATAGRID_minimumColumnHeaderHeight = 4;
         internal const double DATAGRID_maximumStarColumnWidth = 10000;
         internal const double DATAGRID_minimumStarColumnWidth = 0.001;
-        private const double DATAGRID_mouseWheelDelta = 72.0;
+        private const double DATAGRID_mouseWheelDelta = 50.0;
         private const double DATAGRID_maxHeadersThickness = 32768;
 
         private const double DATAGRID_defaultRowHeight = 22;
@@ -2214,32 +2215,71 @@ namespace Avalonia.Controls
         /// <param name="e">PointerWheelEventArgs</param>
         protected override void OnPointerWheelChanged(PointerWheelEventArgs e)
         {
-            if (IsEnabled && !e.Handled && DisplayData.NumDisplayedScrollingElements > 0)
+            e.Handled = e.Handled || UpdateScroll(e.Delta * DATAGRID_mouseWheelDelta);
+        }
+
+        internal bool UpdateScroll(Vector delta)
+        {
+            if (IsEnabled && DisplayData.NumDisplayedScrollingElements > 0)
             {
-                double scrollHeight = 0;
-                if (e.Delta.Y > 0)
+                var handled = false;
+                var scrollHeight = 0d;
+
+                // Vertical scroll handling
+                if (delta.Y > 0)
                 {
-                    scrollHeight = Math.Max(-_verticalOffset, -DATAGRID_mouseWheelDelta);
+                    scrollHeight = Math.Max(-_verticalOffset, -delta.Y);
                 }
-                else if (e.Delta.Y < 0)
+                else if (delta.Y < 0)
                 {
                     if (_vScrollBar != null && VerticalScrollBarVisibility == ScrollBarVisibility.Visible)
                     {
-                        scrollHeight = Math.Min(Math.Max(0, _vScrollBar.Maximum - _verticalOffset), DATAGRID_mouseWheelDelta);
+                        scrollHeight = Math.Min(Math.Max(0, _vScrollBar.Maximum - _verticalOffset), -delta.Y);
                     }
                     else
                     {
                         double maximum = EdgedRowsHeightCalculated - CellsHeight;
-                        scrollHeight = Math.Min(Math.Max(0, maximum - _verticalOffset), DATAGRID_mouseWheelDelta);
+                        scrollHeight = Math.Min(Math.Max(0, maximum - _verticalOffset), -delta.Y);
                     }
                 }
+
                 if (scrollHeight != 0)
                 {
                     DisplayData.PendingVerticalScrollHeight = scrollHeight;
+                    handled = true;
+                }
+
+                // Horizontal scroll handling
+                if (delta.X != 0)
+                {
+                    var originalHorizontalOffset = HorizontalOffset;
+                    var horizontalOffset = originalHorizontalOffset - delta.X;
+                    var widthNotVisible = Math.Max(0, ColumnsInternal.VisibleEdgedColumnsWidth - CellsWidth);
+
+                    if (horizontalOffset < 0)
+                    {
+                        horizontalOffset = 0;
+                    }
+                    if (horizontalOffset > widthNotVisible)
+                    {
+                        horizontalOffset = widthNotVisible;
+                    }
+
+                    if (horizontalOffset != originalHorizontalOffset)
+                    {
+                        HorizontalOffset = horizontalOffset;
+                        handled = true;
+                    }
+                }
+
+                if (handled)
+                {
                     InvalidateRowsMeasure(invalidateIndividualElements: false);
-                    e.Handled = true;
+                    return true;
                 }
             }
+
+            return false;
         }
 
         /// <summary>
@@ -5731,7 +5771,7 @@ namespace Avalonia.Controls
                 {
                     if (SelectionMode == DataGridSelectionMode.Single || !ctrl)
                     {
-                        // Unselect the currectly selected rows except the new selected row
+                        // Unselect the currently selected rows except the new selected row
                         action = DataGridSelectionAction.SelectCurrent;
                     }
                     else

src/Avalonia.Controls.DataGrid/DataGridCell.cs

@@ -173,7 +173,15 @@ namespace Avalonia.Controls
                     }
                     if (OwningRow != null)
                     {
-                        e.Handled = OwningGrid.UpdateStateOnMouseLeftButtonDown(e, ColumnIndex, OwningRow.Slot, !e.Handled);
+                        var handled = OwningGrid.UpdateStateOnMouseLeftButtonDown(e, ColumnIndex, OwningRow.Slot, !e.Handled);
+
+                        // Do not handle PointerPressed with touch,
+                        // so we can start scroll gesture on the same event.
+                        if (e.Pointer.Type != PointerType.Touch)
+                        {
+                            e.Handled = handled;
+                        }
+
                         OwningGrid.UpdatedStateOnMouseLeftButtonDown = true;
                     }
                 }
@@ -197,7 +205,7 @@ namespace Avalonia.Controls
         }
 
         // Makes sure the right gridline has the proper stroke and visibility. If lastVisibleColumn is specified, the 
-        // right gridline will be collapsed if this cell belongs to the lastVisibileColumn and there is no filler column
+        // right gridline will be collapsed if this cell belongs to the lastVisibleColumn and there is no filler column
         internal void EnsureGridLine(DataGridColumn lastVisibleColumn)
         {
             if (OwningGrid != null && _rightGridLine != null)

src/Avalonia.Controls.DataGrid/DataGridCellCoordinates.cs

@@ -40,7 +40,7 @@ namespace Avalonia.Controls
             return false;
         }
 
-        // There is build warning if this is missiing
+        // There is build warning if this is missing
         public override int GetHashCode()
         {
             return base.GetHashCode();

src/Avalonia.Controls.DataGrid/DataGridClipboard.cs

@@ -189,7 +189,7 @@ namespace Avalonia.Controls
         }
 
         /// <summary>
-        /// DataGrid row item used for proparing the ClipboardRowContent.
+        /// DataGrid row item used for preparing the ClipboardRowContent.
         /// </summary>
         public object Item
         {

src/Avalonia.Controls.DataGrid/DataGridColumn.cs

@@ -795,7 +795,7 @@ namespace Avalonia.Controls
         }
 
         /// <summary>
-        /// If the DataGrid is using using layout rounding, the pixel snapping will force all widths to
+        /// If the DataGrid is using layout rounding, the pixel snapping will force all widths to
         /// whole numbers. Since the column widths aren't visual elements, they don't go through the normal
         /// rounding process, so we need to do it ourselves.  If we don't, then we'll end up with some
         /// pixel gaps and/or overlaps between columns.

src/Avalonia.Controls.DataGrid/DataGridDisplayData.cs

@@ -79,7 +79,7 @@ namespace Avalonia.Controls
             set;
         }
 
-        internal void AddRecylableRow(DataGridRow row)
+        internal void AddRecyclableRow(DataGridRow row)
         {
             Debug.Assert(!_recyclableRows.Contains(row));
             row.DetachFromDataGrid(true);
@@ -120,7 +120,7 @@ namespace Avalonia.Controls
                     {
                         if (row.IsRecyclable)
                         {
-                            AddRecylableRow(row);
+                            AddRecyclableRow(row);
                         }
                         else
                         {
@@ -193,7 +193,7 @@ namespace Avalonia.Controls
 
         internal void FullyRecycleElements()
         {
-            // Fully recycle Recycleable rows and transfer them to Recycled rows
+            // Fully recycle Recyclable rows and transfer them to Recycled rows
             while (_recyclableRows.Count > 0)
             {
                 DataGridRow row = _recyclableRows.Pop();
@@ -202,7 +202,7 @@ namespace Avalonia.Controls
                 Debug.Assert(!_fullyRecycledRows.Contains(row));
                 _fullyRecycledRows.Push(row);
             }
-            // Fully recycle Recycleable GroupHeaders and transfer them to Recycled GroupHeaders
+            // Fully recycle Recyclable GroupHeaders and transfer them to Recycled GroupHeaders
             while (_recyclableGroupHeaders.Count > 0)
             {
                 DataGridRowGroupHeader groupHeader = _recyclableGroupHeaders.Pop();

src/Avalonia.Controls.DataGrid/DataGridRow.cs

@@ -392,7 +392,7 @@ namespace Avalonia.Controls
             set;
         }
 
-        // Height that the row will eventually end up at after a possible detalis animation has completed
+        // Height that the row will eventually end up at after a possible details animation has completed
         internal double TargetHeight
         {
             get
@@ -517,7 +517,7 @@ namespace Avalonia.Controls
                 return base.MeasureOverride(availableSize);
             }
 
-            //Allow the DataGrid specific componets to adjust themselves based on new values
+            //Allow the DataGrid specific components to adjust themselves based on new values
             if (_headerElement != null)
             {
                 _headerElement.InvalidateMeasure();
@@ -722,7 +722,7 @@ namespace Avalonia.Controls
                 if (_bottomGridLine != null)
                 {
                     // It looks like setting Visibility sometimes has side effects so make sure the value is actually
-                    // diffferent before setting it
+                    // different before setting it
                     bool newVisibility = OwningGrid.GridLinesVisibility == DataGridGridLinesVisibility.Horizontal || OwningGrid.GridLinesVisibility == DataGridGridLinesVisibility.All;
 
                     if (newVisibility != _bottomGridLine.IsVisible)

src/Avalonia.Controls.DataGrid/DataGridRows.cs

@@ -1193,7 +1193,7 @@ namespace Avalonia.Controls
                 else
                 {
                     groupHeader = element as DataGridRowGroupHeader;
-                    Debug.Assert(groupHeader != null);  // Nothig other and Rows and RowGroups now
+                    Debug.Assert(groupHeader != null);  // Nothing other and Rows and RowGroups now
                     if (groupHeader != null)
                     {
                         groupHeader.TotalIndent = (groupHeader.Level == 0) ? 0 : RowGroupSublevelIndents[groupHeader.Level - 1];
@@ -1636,7 +1636,7 @@ namespace Avalonia.Controls
             if (slot >= DisplayData.FirstScrollingSlot &&
                 slot <= DisplayData.LastScrollingSlot)
             {
-                // Additional row takes the spot of a displayed row - it is necessarilly displayed
+                // Additional row takes the spot of a displayed row - it is necessarily displayed
                 return true;
             }
             else if (DisplayData.FirstScrollingSlot == -1 &&
@@ -1825,7 +1825,7 @@ namespace Avalonia.Controls
                 if (MathUtilities.LessThan(firstRowHeight, NegVerticalOffset))
                 {
                     // We've scrolled off more of the first row than what's possible.  This can happen
-                    // if the first row got shorter (Ex: Collpasing RowDetails) or if the user has a recycling
+                    // if the first row got shorter (Ex: Collapsing RowDetails) or if the user has a recycling
                     // cleanup issue.  In this case, simply try to display the next row as the first row instead
                     if (newFirstScrollingSlot < SlotCount - 1)
                     {
@@ -2014,7 +2014,7 @@ namespace Avalonia.Controls
 
             if (recycleRow)
             {
-                DisplayData.AddRecylableRow(dataGridRow);
+                DisplayData.AddRecyclableRow(dataGridRow);
             }
             else
             {
@@ -2265,7 +2265,7 @@ namespace Avalonia.Controls
                     if (parentGroupInfo.LastSubItemSlot - parentGroupInfo.Slot == 1)
                     {
                         // We just added the first item to a RowGroup so the header should transition from Empty to either Expanded or Collapsed
-                        EnsureAnscestorsExpanderButtonChecked(parentGroupInfo);
+                        EnsureAncestorsExpanderButtonChecked(parentGroupInfo);
                     }
                 }
             }
@@ -2407,7 +2407,7 @@ namespace Avalonia.Controls
             return treeCount;
         }
 
-        private void EnsureAnscestorsExpanderButtonChecked(DataGridRowGroupInfo parentGroupInfo)
+        private void EnsureAncestorsExpanderButtonChecked(DataGridRowGroupInfo parentGroupInfo)
         {
             if (IsSlotVisible(parentGroupInfo.Slot))
             {
@@ -2789,11 +2789,11 @@ namespace Avalonia.Controls
             return null;
         }
 
-        internal void OnRowGroupHeaderToggled(DataGridRowGroupHeader groupHeader, bool newIsVisibile, bool setCurrent)
+        internal void OnRowGroupHeaderToggled(DataGridRowGroupHeader groupHeader, bool newIsVisible, bool setCurrent)
         {
             Debug.Assert(groupHeader.RowGroupInfo.CollectionViewGroup.ItemCount > 0);
 
-            if (WaitForLostFocus(delegate { OnRowGroupHeaderToggled(groupHeader, newIsVisibile, setCurrent); }) || !CommitEdit())
+            if (WaitForLostFocus(delegate { OnRowGroupHeaderToggled(groupHeader, newIsVisible, setCurrent); }) || !CommitEdit())
             {
                 return;
             }
@@ -2804,7 +2804,7 @@ namespace Avalonia.Controls
                 UpdateSelectionAndCurrency(CurrentColumnIndex, groupHeader.RowGroupInfo.Slot, DataGridSelectionAction.SelectCurrent, scrollIntoView: false);
             }
 
-            UpdateRowGroupVisibility(groupHeader.RowGroupInfo, newIsVisibile, isDisplayed: true);
+            UpdateRowGroupVisibility(groupHeader.RowGroupInfo, newIsVisible, isDisplayed: true);
 
             ComputeScrollBarsLayout();
             // We need force arrange since our Scrollings Rows could update without automatically triggering layout

src/Avalonia.Controls.DataGrid/Primitives/DataGridColumnHeadersPresenter.cs

@@ -140,7 +140,7 @@ namespace Avalonia.Controls.Primitives
                 if (dataGridColumn.IsFrozen)
                 {
                     columnHeader.Arrange(new Rect(frozenLeftEdge, 0, dataGridColumn.LayoutRoundedWidth, finalSize.Height));
-                    columnHeader.Clip = null; // The layout system could have clipped this becaues it's not aware of our render transform
+                    columnHeader.Clip = null; // The layout system could have clipped this because it's not aware of our render transform
                     if (DragColumn == dataGridColumn && DragIndicator != null)
                     {
                         dragIndicatorLeftEdge = frozenLeftEdge + DragIndicatorOffset;

src/Avalonia.Controls.DataGrid/Primitives/DataGridRowsPresenter.cs

@@ -5,6 +5,9 @@
 
 using System;
 using System.Diagnostics;
+
+using Avalonia.Input;
+using Avalonia.Input.GestureRecognizers;
 using Avalonia.Layout;
 using Avalonia.Media;
 
@@ -16,6 +19,11 @@ namespace Avalonia.Controls.Primitives
     /// </summary>
     public sealed class DataGridRowsPresenter : Panel
     {
+        public DataGridRowsPresenter()
+        {
+            AddHandler(Gestures.ScrollGestureEvent, OnScrollGesture);
+        }
+
         internal DataGrid OwningGrid
         {
             get;
@@ -176,6 +184,11 @@ namespace Avalonia.Controls.Primitives
             return new Size(totalCellsWidth + headerWidth, totalHeight);
         }
 
+        private void OnScrollGesture(object sender, ScrollGestureEventArgs e)
+        {
+            e.Handled = e.Handled || OwningGrid.UpdateScroll(-e.Delta);
+        }
+
 #if DEBUG
         internal void PrintChildren()
         {

src/Avalonia.Controls.DataGrid/Themes/Default.xaml

@@ -247,7 +247,11 @@
             <DataGridColumnHeader Name="PART_TopRightCornerHeader" Grid.Column="2"/>
             <Rectangle Name="PART_ColumnHeadersAndRowsSeparator" Grid.ColumnSpan="3" VerticalAlignment="Bottom" StrokeThickness="1" Height="1" Fill="{DynamicResource ThemeControlMidHighBrush}"/>
 
-            <DataGridRowsPresenter Name="PART_RowsPresenter" Grid.ColumnSpan="2" Grid.Row="1" />
+            <DataGridRowsPresenter Name="PART_RowsPresenter" Grid.ColumnSpan="2" Grid.Row="1">
+              <DataGridRowsPresenter.GestureRecognizers>
+                <ScrollGestureRecognizer CanHorizontallyScroll="True" CanVerticallyScroll="True" />
+              </DataGridRowsPresenter.GestureRecognizers>
+            </DataGridRowsPresenter>
             <Rectangle Name="PART_BottomRightCorner" Fill="{DynamicResource ThemeControlMidHighBrush}" Grid.Column="2" Grid.Row="2" />
             <Rectangle Name="BottomLeftCorner" Fill="{DynamicResource ThemeControlMidHighBrush}" Grid.Row="2" Grid.ColumnSpan="2" />
             <ScrollBar Name="PART_VerticalScrollbar" Orientation="Vertical" Grid.Column="2" Grid.Row="1" Width="{DynamicResource ScrollBarThickness}"/>

src/Avalonia.Controls.DataGrid/Themes/Fluent.xaml

@@ -601,7 +601,11 @@
             <DataGridRowsPresenter Name="PART_RowsPresenter"
                                    Grid.Row="1"
                                    Grid.RowSpan="2"
-                                   Grid.ColumnSpan="3" />
+                                   Grid.ColumnSpan="3">
+              <DataGridRowsPresenter.GestureRecognizers>
+                <ScrollGestureRecognizer CanHorizontallyScroll="True" CanVerticallyScroll="True" />
+              </DataGridRowsPresenter.GestureRecognizers>
+            </DataGridRowsPresenter>
             <Rectangle Name="PART_BottomRightCorner"
                        Fill="{DynamicResource DataGridScrollBarsSeparatorBackground}"
                        Grid.Column="2"

src/Avalonia.Controls/ApiCompatBaseline.txt

@@ -30,15 +30,29 @@ MembersMustExist : Member 'public System.Double Avalonia.Controls.NumericUpDownV
 MembersMustExist : Member 'public System.Double Avalonia.Controls.NumericUpDownValueChangedEventArgs.OldValue.get()' does not exist in the implementation but it does exist in the contract.
 MembersMustExist : Member 'public Avalonia.StyledProperty<System.Boolean> Avalonia.StyledProperty<System.Boolean> Avalonia.Controls.ScrollViewer.AllowAutoHideProperty' does not exist in the implementation but it does exist in the contract.
 MembersMustExist : Member 'public Avalonia.AvaloniaProperty<Avalonia.Media.Stretch> Avalonia.AvaloniaProperty<Avalonia.Media.Stretch> Avalonia.Controls.Viewbox.StretchProperty' does not exist in the implementation but it does exist in the contract.
-InterfacesShouldHaveSameMembers : Interface member 'public System.EventHandler<System.ComponentModel.CancelEventArgs> Avalonia.Controls.ApplicationLifetimes.IClassicDesktopStyleApplicationLifetime.ShutdownRequested' is present in the implementation but not in the contract.
-InterfacesShouldHaveSameMembers : Interface member 'public void Avalonia.Controls.ApplicationLifetimes.IClassicDesktopStyleApplicationLifetime.add_ShutdownRequested(System.EventHandler<System.ComponentModel.CancelEventArgs>)' is present in the implementation but not in the contract.
-InterfacesShouldHaveSameMembers : Interface member 'public void Avalonia.Controls.ApplicationLifetimes.IClassicDesktopStyleApplicationLifetime.remove_ShutdownRequested(System.EventHandler<System.ComponentModel.CancelEventArgs>)' is present in the implementation but not in the contract.
+InterfacesShouldHaveSameMembers : Interface member 'public System.EventHandler<Avalonia.Controls.ApplicationLifetimes.ShutdownRequestedEventArgs> Avalonia.Controls.ApplicationLifetimes.IClassicDesktopStyleApplicationLifetime.ShutdownRequested' is present in the implementation but not in the contract.
+InterfacesShouldHaveSameMembers : Interface member 'public void Avalonia.Controls.ApplicationLifetimes.IClassicDesktopStyleApplicationLifetime.add_ShutdownRequested(System.EventHandler<Avalonia.Controls.ApplicationLifetimes.ShutdownRequestedEventArgs>)' is present in the implementation but not in the contract.
+InterfacesShouldHaveSameMembers : Interface member 'public void Avalonia.Controls.ApplicationLifetimes.IClassicDesktopStyleApplicationLifetime.remove_ShutdownRequested(System.EventHandler<Avalonia.Controls.ApplicationLifetimes.ShutdownRequestedEventArgs>)' is present in the implementation but not in the contract.
+MembersMustExist : Member 'public System.Action<Avalonia.Size> Avalonia.Controls.Embedding.Offscreen.OffscreenTopLevelImplBase.Resized.get()' does not exist in the implementation but it does exist in the contract.
+MembersMustExist : Member 'public void Avalonia.Controls.Embedding.Offscreen.OffscreenTopLevelImplBase.Resized.set(System.Action<Avalonia.Size>)' does not exist in the implementation but it does exist in the contract.
 MembersMustExist : Member 'public void Avalonia.Controls.Embedding.Offscreen.OffscreenTopLevelImplBase.SetCursor(Avalonia.Platform.IPlatformHandle)' does not exist in the implementation but it does exist in the contract.
 MembersMustExist : Member 'public Avalonia.AvaloniaProperty Avalonia.AvaloniaProperty Avalonia.Controls.Notifications.NotificationCard.CloseOnClickProperty' does not exist in the implementation but it does exist in the contract.
 EnumValuesMustMatch : Enum value 'Avalonia.Platform.ExtendClientAreaChromeHints Avalonia.Platform.ExtendClientAreaChromeHints.Default' is (System.Int32)2 in the implementation but (System.Int32)1 in the contract.
 InterfacesShouldHaveSameMembers : Interface member 'public System.Nullable<Avalonia.Size> Avalonia.Platform.ITopLevelImpl.FrameSize' is present in the implementation but not in the contract.
 InterfacesShouldHaveSameMembers : Interface member 'public System.Nullable<Avalonia.Size> Avalonia.Platform.ITopLevelImpl.FrameSize.get()' is present in the implementation but not in the contract.
+InterfacesShouldHaveSameMembers : Interface member 'public System.Action<Avalonia.Size, Avalonia.Platform.PlatformResizeReason> Avalonia.Platform.ITopLevelImpl.Resized.get()' is present in the implementation but not in the contract.
+InterfacesShouldHaveSameMembers : Interface member 'public System.Action<Avalonia.Size> Avalonia.Platform.ITopLevelImpl.Resized.get()' is present in the contract but not in the implementation.
+MembersMustExist : Member 'public System.Action<Avalonia.Size> Avalonia.Platform.ITopLevelImpl.Resized.get()' does not exist in the implementation but it does exist in the contract.
+InterfacesShouldHaveSameMembers : Interface member 'public void Avalonia.Platform.ITopLevelImpl.Resized.set(System.Action<Avalonia.Size, Avalonia.Platform.PlatformResizeReason>)' is present in the implementation but not in the contract.
+InterfacesShouldHaveSameMembers : Interface member 'public void Avalonia.Platform.ITopLevelImpl.Resized.set(System.Action<Avalonia.Size>)' is present in the contract but not in the implementation.
+MembersMustExist : Member 'public void Avalonia.Platform.ITopLevelImpl.Resized.set(System.Action<Avalonia.Size>)' does not exist in the implementation but it does exist in the contract.
 InterfacesShouldHaveSameMembers : Interface member 'public void Avalonia.Platform.ITopLevelImpl.SetCursor(Avalonia.Platform.ICursorImpl)' is present in the implementation but not in the contract.
 InterfacesShouldHaveSameMembers : Interface member 'public void Avalonia.Platform.ITopLevelImpl.SetCursor(Avalonia.Platform.IPlatformHandle)' is present in the contract but not in the implementation.
 MembersMustExist : Member 'public void Avalonia.Platform.ITopLevelImpl.SetCursor(Avalonia.Platform.IPlatformHandle)' does not exist in the implementation but it does exist in the contract.
-Total Issues: 42
+InterfacesShouldHaveSameMembers : Interface member 'public void Avalonia.Platform.IWindowBaseImpl.Show(System.Boolean)' is present in the contract but not in the implementation.
+MembersMustExist : Member 'public void Avalonia.Platform.IWindowBaseImpl.Show(System.Boolean)' does not exist in the implementation but it does exist in the contract.
+InterfacesShouldHaveSameMembers : Interface member 'public void Avalonia.Platform.IWindowBaseImpl.Show(System.Boolean, System.Boolean)' is present in the implementation but not in the contract.
+InterfacesShouldHaveSameMembers : Interface member 'public void Avalonia.Platform.IWindowImpl.Resize(Avalonia.Size)' is present in the contract but not in the implementation.
+MembersMustExist : Member 'public void Avalonia.Platform.IWindowImpl.Resize(Avalonia.Size)' does not exist in the implementation but it does exist in the contract.
+InterfacesShouldHaveSameMembers : Interface member 'public void Avalonia.Platform.IWindowImpl.Resize(Avalonia.Size, Avalonia.Platform.PlatformResizeReason)' is present in the implementation but not in the contract.
+Total Issues: 56

src/Avalonia.Controls/AppBuilderBase.cs

@@ -273,7 +273,7 @@ namespace Avalonia.Controls
         }
         
         /// <summary>
-        /// Sets up the platform-speciic services for the <see cref="Application"/>.
+        /// Sets up the platform-specific services for the <see cref="Application"/>.
         /// </summary>
         private void Setup()
         {

src/Avalonia.Controls/ApplicationLifetimes/ClassicDesktopStyleApplicationLifetime.cs

@@ -48,7 +48,7 @@ namespace Avalonia.Controls.ApplicationLifetimes
         public event EventHandler<ControlledApplicationLifetimeStartupEventArgs> Startup;
 
         /// <inheritdoc/>
-        public event EventHandler<CancelEventArgs> ShutdownRequested;
+        public event EventHandler<ShutdownRequestedEventArgs> ShutdownRequested;
 
         /// <inheritdoc/>
         public event EventHandler<ControlledApplicationLifetimeExitEventArgs> Exit;
@@ -134,7 +134,7 @@ namespace Avalonia.Controls.ApplicationLifetimes
                 _activeLifetime = null;
         }
         
-        private void OnShutdownRequested(object sender, CancelEventArgs e)
+        private void OnShutdownRequested(object sender, ShutdownRequestedEventArgs e)
         {
             ShutdownRequested?.Invoke(this, e);
 

src/Avalonia.Controls/ApplicationLifetimes/IClassicDesktopStyleApplicationLifetime.cs

@@ -37,14 +37,21 @@ namespace Avalonia.Controls.ApplicationLifetimes
         IReadOnlyList<Window> Windows { get; }
 
         /// <summary>
-        /// Raised by the platform when a shutdown is requested.
+        /// Raised by the platform when an application shutdown is requested.
         /// </summary>
         /// <remarks>
-        /// Raised on on OSX via the Quit menu or right-clicking on the application icon and selecting Quit. This event
-        /// provides a first-chance to cancel application shutdown; if shutdown is not canceled at this point the application
+        /// Application Shutdown can be requested for various reasons like OS shutdown.
+        /// 
+        /// On Windows this will be called when an OS Session (logout or shutdown) terminates. Cancelling the eventargs will 
+        /// block OS shutdown.
+        /// 
+        /// On OSX this has the same behavior as on Windows and in addition:
+        /// This event is raised via the Quit menu or right-clicking on the application icon and selecting Quit. 
+        /// 
+        /// This event provides a first-chance to cancel application shutdown; if shutdown is not canceled at this point the application
         /// will try to close each non-owned open window, invoking the <see cref="Window.Closing"/> event on each and allowing
-        /// each window to cancel the shutdown.
+        /// each window to cancel the shutdown of the application. Windows cannot however prevent OS shutdown.
         /// </remarks>
-        event EventHandler<CancelEventArgs> ShutdownRequested;
+        event EventHandler<ShutdownRequestedEventArgs> ShutdownRequested;
     }
 }

src/Avalonia.Controls/ApplicationLifetimes/ShutdownRequestedEventArgs.cs

@@ -0,0 +1,9 @@
+using System.ComponentModel;
+
+namespace Avalonia.Controls.ApplicationLifetimes
+{
+    public class ShutdownRequestedEventArgs : CancelEventArgs
+    {
+
+    }
+}

src/Avalonia.Controls/AutoCompleteBox.cs

@@ -2005,7 +2005,7 @@ namespace Avalonia.Controls
             // The TextBox.TextChanged event was not firing immediately and
             // was causing an immediate update, even with wrapping. If there is
             // a selection currently, no update should happen.
-            if (IsTextCompletionEnabled && TextBox != null && TextBoxSelectionLength > 0 && TextBoxSelectionStart != TextBox.Text.Length)
+            if (IsTextCompletionEnabled && TextBox != null && TextBoxSelectionLength > 0 && TextBoxSelectionStart != (TextBox.Text?.Length ?? 0))
             {
                 return;
             }
@@ -2303,7 +2303,7 @@ namespace Avalonia.Controls
             {
                 if (IsTextCompletionEnabled && TextBox != null && userInitiated)
                 {
-                    int currentLength = TextBox.Text.Length;
+                    int currentLength = TextBox.Text?.Length ?? 0;
                     int selectionStart = TextBoxSelectionStart;
                     if (selectionStart == text.Length && selectionStart > _textSelectionStart)
                     {

src/Avalonia.Controls/ContextMenu.cs

@@ -2,7 +2,7 @@ using System;
 using System.Collections.Generic;
 using System.ComponentModel;
 using System.Linq;
-
+using Avalonia.Controls.Diagnostics;
 using Avalonia.Controls.Generators;
 using Avalonia.Controls.Platform;
 using Avalonia.Controls.Primitives;
@@ -21,7 +21,7 @@ namespace Avalonia.Controls
     /// <summary>
     /// A control context menu.
     /// </summary>
-    public class ContextMenu : MenuBase, ISetterValue
+    public class ContextMenu : MenuBase, ISetterValue, IPopupHostProvider
     {
         /// <summary>
         /// Defines the <see cref="HorizontalOffset"/> property.
@@ -82,6 +82,7 @@ namespace Avalonia.Controls
         private Popup? _popup;
         private List<Control>? _attachedControls;
         private IInputElement? _previousFocus;
+        private Action<IPopupHost?>? _popupHostChangedHandler;
 
         /// <summary>
         /// Initializes a new instance of the <see cref="ContextMenu"/> class.
@@ -304,6 +305,14 @@ namespace Avalonia.Controls
             }
         }
 
+        IPopupHost? IPopupHostProvider.PopupHost => _popup?.Host;
+
+        event Action<IPopupHost?>? IPopupHostProvider.PopupHostChanged 
+        { 
+            add => _popupHostChangedHandler += value; 
+            remove => _popupHostChangedHandler -= value;
+        }
+
         protected override IItemContainerGenerator CreateItemContainerGenerator()
         {
             return new MenuItemContainerGenerator(this);
@@ -364,6 +373,8 @@ namespace Avalonia.Controls
         {
             _previousFocus = FocusManager.Instance?.Current;
             Focus();
+
+            _popupHostChangedHandler?.Invoke(_popup!.Host);
         }
 
         private void PopupClosing(object sender, CancelEventArgs e)
@@ -397,6 +408,8 @@ namespace Avalonia.Controls
                 RoutedEvent = MenuClosedEvent,
                 Source = this,
             });
+            
+            _popupHostChangedHandler?.Invoke(null);
         }
 
         private void PopupKeyUp(object sender, KeyEventArgs e)

src/Avalonia.Controls/Converters/MarginMultiplierConverter.cs

@@ -26,13 +26,13 @@ namespace Avalonia.Controls.Converters
                     Right ? Indent * scalarDepth : 0,
                     Bottom ? Indent * scalarDepth : 0);
             }
-            else if (value is Thickness thinknessDepth)
+            else if (value is Thickness thicknessDepth)
             {
                 return new Thickness(
-                    Left ? Indent * thinknessDepth.Left : 0,
-                    Top ? Indent * thinknessDepth.Top : 0,
-                    Right ? Indent * thinknessDepth.Right : 0,
-                    Bottom ? Indent * thinknessDepth.Bottom : 0);
+                    Left ? Indent * thicknessDepth.Left : 0,
+                    Top ? Indent * thicknessDepth.Top : 0,
+                    Right ? Indent * thicknessDepth.Right : 0,
+                    Bottom ? Indent * thicknessDepth.Bottom : 0);
             }
             return new Thickness(0);
             

src/Avalonia.Controls/Converters/MenuScrollingVisibilityConverter.cs

@@ -16,7 +16,7 @@ namespace Avalonia.Controls.Converters
             if (parameter == null ||
                 values == null ||
                 values.Count != 4 ||
-                !(values[0] is ScrollBarVisibility visiblity) ||
+                !(values[0] is ScrollBarVisibility visibility) ||
                 !(values[1] is double offset) ||
                 !(values[2] is double extent) ||
                 !(values[3] is double viewport))
@@ -24,7 +24,7 @@ namespace Avalonia.Controls.Converters
                 return AvaloniaProperty.UnsetValue;
             }
 
-            if (visiblity == ScrollBarVisibility.Auto)
+            if (visibility == ScrollBarVisibility.Auto)
             {
                 if (extent == viewport)
                 {

src/Avalonia.Controls/DateTimePickers/DatePicker.cs

@@ -71,7 +71,7 @@ namespace Avalonia.Controls
                 x => x.MonthVisible, (x, v) => x.MonthVisible = v);
 
         /// <summary>
-        /// Defiens the <see cref="YearFormat"/> Property
+        /// Defines the <see cref="YearFormat"/> Property
         /// </summary>
         public static readonly DirectProperty<DatePicker, string> YearFormatProperty =
             AvaloniaProperty.RegisterDirect<DatePicker, string>(nameof(YearFormat), 

src/Avalonia.Controls/DateTimePickers/DateTimePickerPanel.cs

@@ -220,15 +220,15 @@ namespace Avalonia.Controls.Primitives
 
                 if (dy > 0) // Scroll Down
                 {
-                    int numContsToMove = 0;
+                    int numCountsToMove = 0;
                     for (int i = 0; i < children.Count; i++)
                     {
                         if (children[i].Bounds.Bottom - dy < 0)
-                            numContsToMove++;
+                            numCountsToMove++;
                         else
                             break;
                     }
-                    children.MoveRange(0, numContsToMove, children.Count);
+                    children.MoveRange(0, numCountsToMove, children.Count);
 
                     var scrollHeight = _extent.Height - Viewport.Height;
                     if (ShouldLoop && value.Y >= scrollHeight - _extentOne)
@@ -236,15 +236,15 @@ namespace Avalonia.Controls.Primitives
                 }
                 else if (dy < 0) // Scroll Up
                 {
-                    int numContsToMove = 0;
+                    int numCountsToMove = 0;
                     for (int i = children.Count - 1; i >= 0; i--)
                     {
                         if (children[i].Bounds.Top - dy > Bounds.Height)
-                            numContsToMove++;
+                            numCountsToMove++;
                         else
                             break;
                     }
-                    children.MoveRange(children.Count - numContsToMove, numContsToMove, 0);
+                    children.MoveRange(children.Count - numCountsToMove, numCountsToMove, 0);
                     if (ShouldLoop && value.Y < _extentOne)
                         _offset = new Vector(0, value.Y + (_extentOne * 50));
                 }

src/Avalonia.Controls/DefinitionBase.cs

@@ -35,7 +35,7 @@ namespace Avalonia.Controls
             if (_sharedState == null)
             {
                 //  start with getting SharedSizeGroup value. 
-                //  this property is NOT inhereted which should result in better overall perf.
+                //  this property is NOT inherited which should result in better overall perf.
                 string sharedSizeGroupId = SharedSizeGroup;
                 if (sharedSizeGroupId != null)
                 {
@@ -52,7 +52,7 @@ namespace Avalonia.Controls
         }
 
         /// <summary>
-        /// Callback to notify about exitting model tree.
+        /// Callback to notify about exiting model tree.
         /// </summary>
         internal void OnExitParentTree()
         {
@@ -458,7 +458,7 @@ namespace Avalonia.Controls
         private Grid.LayoutTimeSizeType _sizeType;      //  layout-time user size type. it may differ from _userSizeValueCache.UnitType when calculating "to-content"
 
         private double _minSize;                        //  used during measure to accumulate size for "Auto" and "Star" DefinitionBase's
-        private double _measureSize;                    //  size, calculated to be the input contstraint size for Child.Measure
+        private double _measureSize;                    //  size, calculated to be the input constraint size for Child.Measure
         private double _sizeCache;                      //  cache used for various purposes (sorting, caching, etc) during calculations
         private double _offset;                         //  offset of the DefinitionBase from left / top corner (assuming LTR case)
 
@@ -556,7 +556,7 @@ namespace Avalonia.Controls
             }
 
             /// <summary>
-            /// Propogates invalidations for all registered definitions.
+            /// Propagates invalidations for all registered definitions.
             /// Resets its own state.
             /// </summary>
             internal void Invalidate()

src/Avalonia.Controls/Diagnostics/IPopupHostProvider.cs

@@ -0,0 +1,23 @@
+using System;
+using Avalonia.Controls.Primitives;
+
+#nullable enable
+
+namespace Avalonia.Controls.Diagnostics
+{
+    /// <summary>
+    /// Diagnostics interface to retrieve an associated <see cref="IPopupHost"/>.
+    /// </summary>
+    public interface IPopupHostProvider
+    {
+        /// <summary>
+        /// The popup host.
+        /// </summary>
+        IPopupHost? PopupHost { get; }
+
+        /// <summary>
+        /// Raised when the popup host changes.
+        /// </summary>
+        event Action<IPopupHost?>? PopupHostChanged;
+    }
+}

src/Avalonia.Controls/Diagnostics/ToolTipDiagnostics.cs

@@ -0,0 +1,15 @@
+#nullable enable
+
+namespace Avalonia.Controls.Diagnostics
+{
+    /// <summary>
+    /// Helper class to provide diagnostics information for <see cref="ToolTip"/>.
+    /// </summary>
+    public static class ToolTipDiagnostics
+    {
+        /// <summary>
+        /// Provides access to the internal <see cref="ToolTip.ToolTipProperty"/> for use in DevTools.
+        /// </summary>
+        public static AvaloniaProperty<ToolTip?> ToolTipProperty = ToolTip.ToolTipProperty;
+    }
+}

src/Avalonia.Controls/Embedding/Offscreen/OffscreenTopLevelImpl.cs

@@ -31,7 +31,7 @@ namespace Avalonia.Controls.Embedding.Offscreen
             set
             {
                 _clientSize = value;
-                Resized?.Invoke(value);
+                Resized?.Invoke(value, PlatformResizeReason.Unspecified);
             }
         }
 
@@ -49,7 +49,7 @@ namespace Avalonia.Controls.Embedding.Offscreen
         
         public Action<RawInputEventArgs> Input { get; set; }
         public Action<Rect> Paint { get; set; }
-        public Action<Size> Resized { get; set; }
+        public Action<Size, PlatformResizeReason> Resized { get; set; }
         public Action<double> ScalingChanged { get; set; }
 
         public Action<WindowTransparencyLevel> TransparencyLevelChanged { get; set; }

src/Avalonia.Controls/Flyouts/FlyoutBase.cs

@@ -1,19 +1,18 @@
 using System;
 using System.ComponentModel;
+using Avalonia.Controls.Diagnostics;
 using System.Linq;
-
 using Avalonia.Input;
 using Avalonia.Input.Platform;
 using Avalonia.Input.Raw;
 using Avalonia.Layout;
 using Avalonia.Logging;
-using Avalonia.Rendering;
 
 #nullable enable
 
 namespace Avalonia.Controls.Primitives
 {
-    public abstract class FlyoutBase : AvaloniaObject
+    public abstract class FlyoutBase : AvaloniaObject, IPopupHostProvider
     {
         static FlyoutBase()
         {
@@ -59,6 +58,7 @@ namespace Avalonia.Controls.Primitives
         private Rect? _enlargedPopupRect;
         private PixelRect? _enlargePopupRectScreenPixelRect;
         private IDisposable? _transientDisposable;
+        private Action<IPopupHost?>? _popupHostChangedHandler;
 
         public FlyoutBase()
         {
@@ -103,6 +103,14 @@ namespace Avalonia.Controls.Primitives
             private set => SetAndRaise(TargetProperty, ref _target, value);
         }
 
+        IPopupHost? IPopupHostProvider.PopupHost => Popup?.Host;
+
+        event Action<IPopupHost?>? IPopupHostProvider.PopupHostChanged 
+        { 
+            add => _popupHostChangedHandler += value; 
+            remove => _popupHostChangedHandler -= value;
+        }
+
         public event EventHandler? Closed;
         public event EventHandler<CancelEventArgs>? Closing;
         public event EventHandler? Opened;
@@ -363,6 +371,8 @@ namespace Avalonia.Controls.Primitives
         private void OnPopupOpened(object sender, EventArgs e)
         {
             IsOpen = true;
+
+            _popupHostChangedHandler?.Invoke(Popup!.Host);
         }
 
         private void OnPopupClosing(object sender, CancelEventArgs e)
@@ -376,6 +386,8 @@ namespace Avalonia.Controls.Primitives
         private void OnPopupClosed(object sender, EventArgs e)
         {
             HideCore(false);
+
+            _popupHostChangedHandler?.Invoke(null);
         }
 
         // This method is handling both popup logical tree and target logical tree.
@@ -552,7 +564,7 @@ namespace Avalonia.Controls.Primitives
 
         internal static void SetPresenterClasses(IControl presenter, Classes classes)
         {
-            //Remove any classes no longer in use, ignoring pseudoclasses
+            //Remove any classes no longer in use, ignoring pseudo classes
             for (int i = presenter.Classes.Count - 1; i >= 0; i--)
             {
                 if (!classes.Contains(presenter.Classes[i]) &&

src/Avalonia.Controls/Flyouts/FlyoutPresenter.cs

@@ -6,15 +6,6 @@ namespace Avalonia.Controls
 {
     public class FlyoutPresenter : ContentControl
     {
-        public static readonly StyledProperty<CornerRadius> CornerRadiusProperty =
-            Border.CornerRadiusProperty.AddOwner<FlyoutPresenter>();
-
-        public CornerRadius CornerRadius
-        {
-            get => GetValue(CornerRadiusProperty);
-            set => SetValue(CornerRadiusProperty, value);
-        }
-
         protected override void OnKeyDown(KeyEventArgs e)
         {
             if (e.Key == Key.Escape)

src/Avalonia.Controls/Grid.cs

@@ -330,7 +330,7 @@ namespace Avalonia.Controls
                     //  value of Auto column), "cell 2 1" needs to be calculated first,
                     //  as it contributes to the Auto column's calculated value.
                     //  At the same time in order to accurately calculate constraint
-                    //  height for "cell 2 1", "cell 1 2" needs to be calcualted first,
+                    //  height for "cell 2 1", "cell 1 2" needs to be calculated first,
                     //  as it contributes to Auto row height, which is used in the
                     //  computation of Star row resolved height.
                     //
@@ -405,11 +405,11 @@ namespace Avalonia.Controls
                     //
                     //  where:
                     //  *   all [Measure GroupN] - regular children measure process -
-                    //      each cell is measured given contraint size as an input
+                    //      each cell is measured given constraint size as an input
                     //      and each cell's desired size is accumulated on the
                     //      corresponding column / row;
                     //  *   [Measure Group2'] - is when each cell is measured with
-                    //      infinit height as a constraint and a cell's desired
+                    //      infinite height as a constraint and a cell's desired
                     //      height is ignored;
                     //  *   [Measure Groups''] - is when each cell is measured (second
                     //      time during single Grid.MeasureOverride) regularly but its
@@ -780,7 +780,7 @@ namespace Avalonia.Controls
         }
 
         /// <summary>
-        /// Initializes DefinitionsU memeber either to user supplied ColumnDefinitions collection
+        /// Initializes DefinitionsU member either to user supplied ColumnDefinitions collection
         /// or to a default single element collection. DefinitionsU gets trimmed to size.
         /// </summary>
         /// <remarks>
@@ -821,7 +821,7 @@ namespace Avalonia.Controls
         }
 
         /// <summary>
-        /// Initializes DefinitionsV memeber either to user supplied RowDefinitions collection
+        /// Initializes DefinitionsV member either to user supplied RowDefinitions collection
         /// or to a default single element collection. DefinitionsV gets trimmed to size.
         /// </summary>
         /// <remarks>
@@ -2132,7 +2132,7 @@ namespace Avalonia.Controls
                 //
                 // Fortunately, our scenarios tend to have a small number of columns (~10 or fewer)
                 // each being allocated a large number of pixels (~50 or greater), and
-                // people don't even notice the kind of 1-pixel anomolies that are
+                // people don't even notice the kind of 1-pixel anomalies that are
                 // theoretically inevitable, or don't care if they do.  At least they shouldn't
                 // care - no one should be using the results WPF's grid layout to make
                 // quantitative decisions; its job is to produce a reasonable display, not
@@ -2597,7 +2597,7 @@ namespace Avalonia.Controls
             if (scale < 0.0)
             {
                 // if one of the *-weights is Infinity, adjust the weights by mapping
-                // Infinty to 1.0 and everything else to 0.0:  the infinite items share the
+                // Infinity to 1.0 and everything else to 0.0:  the infinite items share the
                 // available space equally, everyone else gets nothing.
                 return (Double.IsPositiveInfinity(def.UserSize.Value)) ? 1.0 : 0.0;
             }
@@ -2655,7 +2655,7 @@ namespace Avalonia.Controls
         private enum Flags
         {
             //
-            //  the foolowing flags let grid tracking dirtiness in more granular manner:
+            //  the following flags let grid tracking dirtiness in more granular manner:
             //  * Valid???Structure flags indicate that elements were added or removed.
             //  * Valid???Layout flags indicate that layout time portion of the information
             //    stored on the objects should be updated.
@@ -2684,7 +2684,7 @@ namespace Avalonia.Controls
 
         /// <summary>
         /// ShowGridLines property. This property is used mostly
-        /// for simplification of visual debuggig. When it is set
+        /// for simplification of visual debugging. When it is set
         /// to <c>true</c> grid lines are drawn to visualize location
         /// of grid lines.
         /// </summary>

src/Avalonia.Controls/ListBox.cs

@@ -89,7 +89,7 @@ namespace Avalonia.Controls
         /// </summary>
         /// <remarks>
         /// Note that the selection mode only applies to selections made via user interaction.
-        /// Multiple selections can be made programatically regardless of the value of this property.
+        /// Multiple selections can be made programmatically regardless of the value of this property.
         /// </remarks>
         public new SelectionMode SelectionMode
         {

src/Avalonia.Controls/NativeMenuItemSeparator.cs

@@ -3,7 +3,7 @@
 namespace Avalonia.Controls
 {
 
-    [Obsolete("This class exists to maintain backwards compatiblity with existing code. Use NativeMenuItemSeparator instead")]
+    [Obsolete("This class exists to maintain backwards compatibility with existing code. Use NativeMenuItemSeparator instead")]
     public class NativeMenuItemSeperator : NativeMenuItemSeparator 
     {
     }

src/Avalonia.Controls/Platform/ExtendClientAreaChromeHints.cs

@@ -25,7 +25,7 @@ namespace Avalonia.Platform
 
         /// <summary>
         /// Use system chrome where possible. OSX system chrome is used, Windows managed chrome is used.
-        /// This is because Windows Chrome can not be shown ontop of user content.
+        /// This is because Windows Chrome can not be shown on top of user content.
         /// </summary>
         PreferSystemChrome = 0x02,
 

src/Avalonia.Controls/Platform/IPlatformLifetimeEventsImpl.cs

@@ -1,5 +1,6 @@
 using System;
 using System.ComponentModel;
+using Avalonia.Controls.ApplicationLifetimes;
 
 namespace Avalonia.Platform
 {
@@ -11,6 +12,6 @@ namespace Avalonia.Platform
         /// <remarks>
         /// Raised on on OSX via the Quit menu or right-clicking on the application icon and selecting Quit.
         /// </remarks>
-        event EventHandler<CancelEventArgs> ShutdownRequested;
+        event EventHandler<ShutdownRequestedEventArgs> ShutdownRequested;
     }
 }

src/Avalonia.Controls/Platform/ITopLevelImpl.cs

@@ -3,11 +3,46 @@ using System.Collections.Generic;
 using Avalonia.Controls;
 using Avalonia.Input;
 using Avalonia.Input.Raw;
+using Avalonia.Layout;
 using Avalonia.Rendering;
 using JetBrains.Annotations;
 
 namespace Avalonia.Platform
 {
+    /// <summary>
+    /// Describes the reason for a <see cref="ITopLevelImpl.Resized"/> message.
+    /// </summary>
+    public enum PlatformResizeReason
+    {
+        /// <summary>
+        /// The resize reason is unknown or unspecified.
+        /// </summary>
+        Unspecified,
+
+        /// <summary>
+        /// The resize was due to the user resizing the window, for example by dragging the
+        /// window frame.
+        /// </summary>
+        User,
+
+        /// <summary>
+        /// The resize was initiated by the application, for example by setting one of the sizing-
+        /// related properties on <see cref="Window"/> such as <see cref="Layoutable.Width"/> or
+        /// <see cref="Layoutable.Height"/>.
+        /// </summary>
+        Application,
+
+        /// <summary>
+        /// The resize was initiated by the layout system.
+        /// </summary>
+        Layout,
+
+        /// <summary>
+        /// The resize was due to a change in DPI.
+        /// </summary>
+        DpiChange,
+    }
+
     /// <summary>
     /// Defines a platform-specific top-level window implementation.
     /// </summary>
@@ -57,7 +92,7 @@ namespace Avalonia.Platform
         /// <summary>
         /// Gets or sets a method called when the toplevel is resized.
         /// </summary>
-        Action<Size> Resized { get; set; }
+        Action<Size, PlatformResizeReason> Resized { get; set; }
 
         /// <summary>
         /// Gets or sets a method called when the toplevel's scaling changes.

src/Avalonia.Controls/Platform/IWindowBaseImpl.cs

@@ -7,7 +7,9 @@ namespace Avalonia.Platform
         /// <summary>
         /// Shows the window.
         /// </summary>
-        void Show(bool activate);
+        /// <param name="activate">Whether to activate the shown window.</param>
+        /// <param name="isDialog">Whether the window is being shown as a dialog.</param>
+        void Show(bool activate, bool isDialog);
 
         /// <summary>
         /// Hides the window.

src/Avalonia.Controls/Platform/IWindowImpl.cs

@@ -110,7 +110,9 @@ namespace Avalonia.Platform
         /// <summary>
         /// Sets the client size of the top level.
         /// </summary>
-        void Resize(Size clientSize);
+        /// <param name="clientSize">The new client size.</param>
+        /// <param name="reason">The reason for the resize.</param>
+        void Resize(Size clientSize, PlatformResizeReason reason = PlatformResizeReason.Application);
 
         /// <summary>
         /// Sets the client size of the top level.

src/Avalonia.Controls/Platform/InternalPlatformThreadingInterface.cs

@@ -21,10 +21,12 @@ namespace Avalonia.Controls.Platform
 
         public void RunLoop(CancellationToken cancellationToken)
         {
-            while (true)
+            var handles = new[] { _signaled, cancellationToken.WaitHandle };
+
+            while (!cancellationToken.IsCancellationRequested)
             {
                 Signaled?.Invoke(null);
-                _signaled.WaitOne();
+                WaitHandle.WaitAny(handles);
             }
         }
 

src/Avalonia.Controls/Primitives/AdornerLayer.cs

@@ -183,7 +183,7 @@ namespace Avalonia.Controls.Primitives
                 info.Subscription = adorned.GetObservable(TransformedBoundsProperty).Subscribe(x =>
                 {
                     info.Bounds = x;
-                    InvalidateArrange();
+                    InvalidateMeasure();
                 });
             }
         }

src/Avalonia.Controls/Primitives/OverlayPopupHost.cs

@@ -140,10 +140,5 @@ namespace Avalonia.Controls.Primitives
 
             return new OverlayPopupHost(overlayLayer);
         }
-
-        public override void Render(DrawingContext context)
-        {
-            context.FillRectangle(Brushes.White, new Rect(default, Bounds.Size));
-        }
     }
 }

src/Avalonia.Controls/Primitives/Popup.cs

@@ -2,6 +2,7 @@ using System;
 using System.ComponentModel;
 using System.Linq;
 using System.Reactive.Disposables;
+using Avalonia.Controls.Diagnostics;
 using Avalonia.Controls.Presenters;
 using Avalonia.Controls.Primitives.PopupPositioning;
 using Avalonia.Input;
@@ -18,7 +19,7 @@ namespace Avalonia.Controls.Primitives
     /// <summary>
     /// Displays a popup window.
     /// </summary>
-    public class Popup : Control, IVisualTreeHost
+    public class Popup : Control, IVisualTreeHost, IPopupHostProvider
     {
         public static readonly StyledProperty<bool> WindowManagerAddShadowHintProperty =
             AvaloniaProperty.Register<PopupRoot, bool>(nameof(WindowManagerAddShadowHint), true);
@@ -134,6 +135,7 @@ namespace Avalonia.Controls.Primitives
         private bool _ignoreIsOpenChanged;
         private PopupOpenState? _openState;
         private IInputElement _overlayInputPassThroughElement;
+        private Action<IPopupHost?>? _popupHostChangedHandler;
 
         /// <summary>
         /// Initializes static members of the <see cref="Popup"/> class.
@@ -351,6 +353,14 @@ namespace Avalonia.Controls.Primitives
         /// </summary>
         IVisual? IVisualTreeHost.Root => _openState?.PopupHost.HostedVisualTreeRoot;
 
+        IPopupHost? IPopupHostProvider.PopupHost => Host;
+
+        event Action<IPopupHost?>? IPopupHostProvider.PopupHostChanged 
+        { 
+            add => _popupHostChangedHandler += value; 
+            remove => _popupHostChangedHandler -= value;
+        }
+
         /// <summary>
         /// Opens the popup.
         /// </summary>
@@ -482,6 +492,8 @@ namespace Avalonia.Controls.Primitives
             }
 
             Opened?.Invoke(this, EventArgs.Empty);
+
+            _popupHostChangedHandler?.Invoke(Host);
         }
 
         /// <summary>
@@ -591,6 +603,8 @@ namespace Avalonia.Controls.Primitives
             _openState.Dispose();
             _openState = null;
 
+            _popupHostChangedHandler?.Invoke(null);
+
             using (BeginIgnoringIsOpen())
             {
                 IsOpen = false;

src/Avalonia.Controls/Primitives/PopupPositioning/ManagedPopupPositioner.cs

@@ -27,7 +27,7 @@ namespace Avalonia.Controls.Primitives.PopupPositioning
 
     /// <summary>
     /// An <see cref="IPopupPositioner"/> implementation for platforms on which a popup can be
-    /// aritrarily positioned.
+    /// arbitrarily positioned.
     /// </summary>
     public class ManagedPopupPositioner : IPopupPositioner
     {

src/Avalonia.Controls/Primitives/PopupRoot.cs

@@ -161,12 +161,9 @@ namespace Avalonia.Controls.Primitives
 
         protected override sealed Size ArrangeSetBounds(Size size)
         {
-            using (BeginAutoSizing())
-            {
-                _positionerParameters.Size = size;
-                UpdatePosition();
-                return ClientSize;
-            }
+            _positionerParameters.Size = size;
+            UpdatePosition();
+            return ClientSize;
         }
     }
 }

src/Avalonia.Controls/Primitives/RangeBase.cs

@@ -170,7 +170,7 @@ namespace Avalonia.Controls.Primitives
         }
 
         /// <summary>
-        /// Checks if the double value is not inifinity nor NaN.
+        /// Checks if the double value is not infinity nor NaN.
         /// </summary>
         /// <param name="value">The value.</param>
         private static bool ValidateDouble(double value)

src/Avalonia.Controls/Primitives/ScrollBar.cs

@@ -57,6 +57,18 @@ namespace Avalonia.Controls.Primitives
         public static readonly StyledProperty<bool> AllowAutoHideProperty =
             AvaloniaProperty.Register<ScrollBar, bool>(nameof(AllowAutoHide), true);
 
+        /// <summary>
+        /// Defines the <see cref="HideDelay"/> property.
+        /// </summary>
+        public static readonly StyledProperty<TimeSpan> HideDelayProperty =
+            AvaloniaProperty.Register<ScrollBar, TimeSpan>(nameof(HideDelay), TimeSpan.FromSeconds(2));
+
+        /// <summary>
+        /// Defines the <see cref="ShowDelay"/> property.
+        /// </summary>
+        public static readonly StyledProperty<TimeSpan> ShowDelayProperty =
+            AvaloniaProperty.Register<ScrollBar, TimeSpan>(nameof(ShowDelay), TimeSpan.FromSeconds(0.5));
+
         private Button _lineUpButton;
         private Button _lineDownButton;
         private Button _pageUpButton;
@@ -126,6 +138,24 @@ namespace Avalonia.Controls.Primitives
             get => GetValue(AllowAutoHideProperty);
             set => SetValue(AllowAutoHideProperty, value);
         }
+        
+        /// <summary>
+        /// Gets a value that determines how long will be the hide delay after user stops interacting with the scrollbar.
+        /// </summary>
+        public TimeSpan HideDelay
+        {
+            get => GetValue(HideDelayProperty);
+            set => SetValue(HideDelayProperty, value);
+        }
+        
+        /// <summary>
+        /// Gets a value that determines how long will be the show delay when user starts interacting with the scrollbar.
+        /// </summary>
+        public TimeSpan ShowDelay
+        {
+            get => GetValue(ShowDelayProperty);
+            set => SetValue(ShowDelayProperty, value);
+        }
 
         public event EventHandler<ScrollEventArgs> Scroll;
 
@@ -296,12 +326,12 @@ namespace Avalonia.Controls.Primitives
 
         private void CollapseAfterDelay()
         {
-            InvokeAfterDelay(Collapse, TimeSpan.FromSeconds(2));
+            InvokeAfterDelay(Collapse, HideDelay);
         }
 
         private void ExpandAfterDelay()
         {
-            InvokeAfterDelay(Expand, TimeSpan.FromMilliseconds(400));
+            InvokeAfterDelay(Expand, ShowDelay);
         }
 
         private void Collapse()

src/Avalonia.Controls/Primitives/SelectingItemsControl.cs

@@ -328,7 +328,7 @@ namespace Avalonia.Controls.Primitives
         /// </summary>
         /// <remarks>
         /// Note that the selection mode only applies to selections made via user interaction.
-        /// Multiple selections can be made programatically regardless of the value of this property.
+        /// Multiple selections can be made programmatically regardless of the value of this property.
         /// </remarks>
         protected SelectionMode SelectionMode
         {

src/Avalonia.Controls/Primitives/TemplatedControl.cs

@@ -5,7 +5,8 @@ using Avalonia.Logging;
 using Avalonia.LogicalTree;
 using Avalonia.Media;
 using Avalonia.Styling;
-using Avalonia.VisualTree;
+
+#nullable enable
 
 namespace Avalonia.Controls.Primitives
 {
@@ -17,13 +18,13 @@ namespace Avalonia.Controls.Primitives
         /// <summary>
         /// Defines the <see cref="Background"/> property.
         /// </summary>
-        public static readonly StyledProperty<IBrush> BackgroundProperty =
+        public static readonly StyledProperty<IBrush?> BackgroundProperty =
             Border.BackgroundProperty.AddOwner<TemplatedControl>();
 
         /// <summary>
         /// Defines the <see cref="BorderBrush"/> property.
         /// </summary>
-        public static readonly StyledProperty<IBrush> BorderBrushProperty =
+        public static readonly StyledProperty<IBrush?> BorderBrushProperty =
             Border.BorderBrushProperty.AddOwner<TemplatedControl>();
 
         /// <summary>
@@ -32,6 +33,12 @@ namespace Avalonia.Controls.Primitives
         public static readonly StyledProperty<Thickness> BorderThicknessProperty =
             Border.BorderThicknessProperty.AddOwner<TemplatedControl>();
 
+        /// <summary>
+        /// Defines the <see cref="CornerRadius"/> property.
+        /// </summary>
+        public static readonly StyledProperty<CornerRadius> CornerRadiusProperty =
+            Border.CornerRadiusProperty.AddOwner<TemplatedControl>();
+
         /// <summary>
         /// Defines the <see cref="FontFamily"/> property.
         /// </summary>
@@ -59,7 +66,7 @@ namespace Avalonia.Controls.Primitives
         /// <summary>
         /// Defines the <see cref="Foreground"/> property.
         /// </summary>
-        public static readonly StyledProperty<IBrush> ForegroundProperty =
+        public static readonly StyledProperty<IBrush?> ForegroundProperty =
             TextBlock.ForegroundProperty.AddOwner<TemplatedControl>();
 
         /// <summary>
@@ -71,8 +78,8 @@ namespace Avalonia.Controls.Primitives
         /// <summary>
         /// Defines the <see cref="Template"/> property.
         /// </summary>
-        public static readonly StyledProperty<IControlTemplate> TemplateProperty =
-            AvaloniaProperty.Register<TemplatedControl, IControlTemplate>(nameof(Template));
+        public static readonly StyledProperty<IControlTemplate?> TemplateProperty =
+            AvaloniaProperty.Register<TemplatedControl, IControlTemplate?>(nameof(Template));
 
         /// <summary>
         /// Defines the IsTemplateFocusTarget attached property.
@@ -88,7 +95,7 @@ namespace Avalonia.Controls.Primitives
                 "TemplateApplied", 
                 RoutingStrategies.Direct);
 
-        private IControlTemplate _appliedTemplate;
+        private IControlTemplate? _appliedTemplate;
 
         /// <summary>
         /// Initializes static members of the <see cref="TemplatedControl"/> class.
@@ -111,7 +118,7 @@ namespace Avalonia.Controls.Primitives
         /// <summary>
         /// Gets or sets the brush used to draw the control's background.
         /// </summary>
-        public IBrush Background
+        public IBrush? Background
         {
             get { return GetValue(BackgroundProperty); }
             set { SetValue(BackgroundProperty, value); }
@@ -120,7 +127,7 @@ namespace Avalonia.Controls.Primitives
         /// <summary>
         /// Gets or sets the brush used to draw the control's border.
         /// </summary>
-        public IBrush BorderBrush
+        public IBrush? BorderBrush
         {
             get { return GetValue(BorderBrushProperty); }
             set { SetValue(BorderBrushProperty, value); }
@@ -135,6 +142,15 @@ namespace Avalonia.Controls.Primitives
             set { SetValue(BorderThicknessProperty, value); }
         }
 
+        /// <summary>
+        /// Gets or sets the radius of the border rounded corners.
+        /// </summary>
+        public CornerRadius CornerRadius
+        {
+            get { return GetValue(CornerRadiusProperty); }
+            set { SetValue(CornerRadiusProperty, value); }
+        }
+
         /// <summary>
         /// Gets or sets the font family used to draw the control's text.
         /// </summary>
@@ -174,7 +190,7 @@ namespace Avalonia.Controls.Primitives
         /// <summary>
         /// Gets or sets the brush used to draw the control's text and other foreground elements.
         /// </summary>
-        public IBrush Foreground
+        public IBrush? Foreground
         {
             get { return GetValue(ForegroundProperty); }
             set { SetValue(ForegroundProperty, value); }
@@ -192,7 +208,7 @@ namespace Avalonia.Controls.Primitives
         /// <summary>
         /// Gets or sets the template that defines the control's appearance.
         /// </summary>
-        public IControlTemplate Template
+        public IControlTemplate? Template
         {
             get { return GetValue(TemplateProperty); }
             set { SetValue(TemplateProperty, value); }
@@ -265,7 +281,9 @@ namespace Avalonia.Controls.Primitives
 
                     var e = new TemplateAppliedEventArgs(nameScope);
                     OnApplyTemplate(e);
+#pragma warning disable CS0618 // Type or member is obsolete
                     OnTemplateApplied(e);
+#pragma warning restore CS0618 // Type or member is obsolete
                     RaiseEvent(e);
                 }
 

src/Avalonia.Controls/Repeater/IElementFactory.cs

@@ -46,7 +46,7 @@ namespace Avalonia.Controls
     }
 
     /// <summary>
-    /// A data template that supports creating and recyling elements for an <see cref="ItemsRepeater"/>.
+    /// A data template that supports creating and recycling elements for an <see cref="ItemsRepeater"/>.
     /// </summary>
     public interface IElementFactory : IDataTemplate
     {

src/Avalonia.Controls/Repeater/ItemsRepeater.cs

@@ -441,9 +441,9 @@ namespace Avalonia.Controls
             base.OnPropertyChanged(change);
         }
 
-        internal IControl GetElementImpl(int index, bool forceCreate, bool supressAutoRecycle)
+        internal IControl GetElementImpl(int index, bool forceCreate, bool suppressAutoRecycle)
         {
-            var element = _viewManager.GetElement(index, forceCreate, supressAutoRecycle);
+            var element = _viewManager.GetElement(index, forceCreate, suppressAutoRecycle);
             return element;
         }
 

src/Avalonia.Controls/Repeater/ViewManager.cs

@@ -174,7 +174,7 @@ namespace Avalonia.Controls
             }
             else
             {
-                // We could not find a candiate.
+                // We could not find a candidate.
                 _lastFocusedElement = null;
             }
         }

src/Avalonia.Controls/Repeater/ViewportManager.cs

@@ -186,7 +186,7 @@ namespace Avalonia.Controls
                 _expectedViewportShift.X + _layoutExtent.X - extent.X,
                 _expectedViewportShift.Y + _layoutExtent.Y - extent.Y);
 
-            // We tolerate viewport imprecisions up to 1 pixel to avoid invaliding layout too much.
+            // We tolerate viewport imprecisions up to 1 pixel to avoid invalidating layout too much.
             if (Math.Abs(_expectedViewportShift.X) > 1 || Math.Abs(_expectedViewportShift.Y) > 1)
             {
                 Logger.TryGet(LogEventLevel.Verbose, "Repeater")?.Log(this, "{LayoutId}: Expecting viewport shift of ({Shift})",

src/Avalonia.Controls/ScrollViewer.cs

@@ -653,7 +653,7 @@ namespace Avalonia.Controls
         private void CalculatedPropertiesChanged()
         {
             // Pass old values of 0 here because we don't have the old values at this point,
-            // and it shouldn't matter as only the template uses these properies.
+            // and it shouldn't matter as only the template uses these properties.
             RaisePropertyChanged(HorizontalScrollBarMaximumProperty, 0, HorizontalScrollBarMaximum);
             RaisePropertyChanged(HorizontalScrollBarValueProperty, 0, HorizontalScrollBarValue);
             RaisePropertyChanged(HorizontalScrollBarViewportSizeProperty, 0, HorizontalScrollBarViewportSize);

src/Avalonia.Controls/Selection/SelectionModel.cs

@@ -345,7 +345,7 @@ namespace Avalonia.Controls.Selection
         private protected override void OnSelectionChanged(IReadOnlyList<T> deselectedItems)
         {
             // Note: We're *not* putting this in a using scope. A collection update is still in progress
-            // so the operation won't get commited by normal means: we have to commit it manually.
+            // so the operation won't get committed by normal means: we have to commit it manually.
             var update = BatchUpdate();
 
             update.Operation.DeselectedItems = deselectedItems;

src/Avalonia.Controls/TextBox.cs

@@ -31,7 +31,7 @@ namespace Avalonia.Controls
 
         public static KeyGesture PasteGesture { get; } = AvaloniaLocator.Current
             .GetService<PlatformHotkeyConfiguration>()?.Paste.FirstOrDefault();
-        
+
         public static readonly StyledProperty<bool> AcceptsReturnProperty =
             AvaloniaProperty.Register<TextBox, bool>(nameof(AcceptsReturn));
 
@@ -117,7 +117,7 @@ namespace Avalonia.Controls
 
         public static readonly StyledProperty<bool> RevealPasswordProperty =
             AvaloniaProperty.Register<TextBox, bool>(nameof(RevealPassword));
-        
+
         public static readonly DirectProperty<TextBox, bool> CanCutProperty =
             AvaloniaProperty.RegisterDirect<TextBox, bool>(
                 nameof(CanCut),
@@ -135,7 +135,7 @@ namespace Avalonia.Controls
 
         public static readonly StyledProperty<bool> IsUndoEnabledProperty =
             AvaloniaProperty.Register<TextBox, bool>(
-                nameof(IsUndoEnabled), 
+                nameof(IsUndoEnabled),
                 defaultValue: true);
 
         public static readonly DirectProperty<TextBox, int> UndoLimitProperty =
@@ -157,6 +157,10 @@ namespace Avalonia.Controls
             }
 
             public bool Equals(UndoRedoState other) => ReferenceEquals(Text, other.Text) || Equals(Text, other.Text);
+
+            public override bool Equals(object obj) => obj is UndoRedoState other && Equals(other);
+
+            public override int GetHashCode() => Text.GetHashCode();
         }
 
         private string _text;
@@ -174,6 +178,10 @@ namespace Avalonia.Controls
         private string _newLine = Environment.NewLine;
         private static readonly string[] invalidCharacters = new String[1] { "\u007f" };
 
+        private int _selectedTextChangesMadeSinceLastUndoSnapshot;
+        private bool _hasDoneSnapshotOnce;
+        private const int _maxCharsBeforeUndoSnapshot = 7;
+
         static TextBox()
         {
             FocusableProperty.OverrideDefaultValue(typeof(TextBox), true);
@@ -202,7 +210,8 @@ namespace Avalonia.Controls
                 horizontalScrollBarVisibility,
                 BindingPriority.Style);
             _undoRedoHelper = new UndoRedoHelper<UndoRedoState>(this);
-
+            _selectedTextChangesMadeSinceLastUndoSnapshot = 0;
+            _hasDoneSnapshotOnce = false;
             UpdatePseudoclasses();
         }
 
@@ -331,6 +340,7 @@ namespace Avalonia.Controls
                     if (SetAndRaise(TextProperty, ref _text, value) && IsUndoEnabled && !_isUndoingRedoing)
                     {
                         _undoRedoHelper.Clear();
+                        SnapshotUndoRedo(); // so we always have an initial state
                     }
                 }
             }
@@ -341,16 +351,16 @@ namespace Avalonia.Controls
             get { return GetSelection(); }
             set
             {
-                SnapshotUndoRedo();
                 if (string.IsNullOrEmpty(value))
                 {
+                    _selectedTextChangesMadeSinceLastUndoSnapshot++;
+                    SnapshotUndoRedo(ignoreChangeCount: false);
                     DeleteSelection();
                 }
                 else
                 {
                     HandleTextInput(value);
                 }
-                SnapshotUndoRedo();
             }
         }
 
@@ -422,7 +432,7 @@ namespace Avalonia.Controls
             get { return _newLine; }
             set { SetAndRaise(NewLineProperty, ref _newLine, value); }
         }
-        
+
         /// <summary>
         /// Clears the current selection, maintaining the <see cref="CaretIndex"/>
         /// </summary>
@@ -480,11 +490,13 @@ namespace Avalonia.Controls
                     var oldValue = _undoRedoHelper.Limit;
                     _undoRedoHelper.Limit = value;
                     RaisePropertyChanged(UndoLimitProperty, oldValue, value);
-                } 
+                }
                 // from docs at
                 // https://docs.microsoft.com/en-us/dotnet/api/system.windows.controls.primitives.textboxbase.isundoenabled:
                 // "Setting UndoLimit clears the undo queue."
                 _undoRedoHelper.Clear();
+                _selectedTextChangesMadeSinceLastUndoSnapshot = 0;
+                _hasDoneSnapshotOnce = false;
             }
         }
 
@@ -515,6 +527,8 @@ namespace Avalonia.Controls
                 // Therefore, if you disable undo and then re-enable it, undo commands still do not work
                 // because the undo stack was emptied when you disabled undo."
                 _undoRedoHelper.Clear();
+                _selectedTextChangesMadeSinceLastUndoSnapshot = 0;
+                _hasDoneSnapshotOnce = false;
             }
         }
 
@@ -577,23 +591,25 @@ namespace Avalonia.Controls
             {
                 return;
             }
-            
+
             input = RemoveInvalidCharacters(input);
-            
+
             if (string.IsNullOrEmpty(input))
             {
                 return;
             }
-            
+            _selectedTextChangesMadeSinceLastUndoSnapshot++;
+            SnapshotUndoRedo(ignoreChangeCount: false);
+
             string text = Text ?? string.Empty;
             int caretIndex = CaretIndex;
             int newLength = input.Length + text.Length - Math.Abs(SelectionStart - SelectionEnd);
-            
+
             if (MaxLength > 0 && newLength > MaxLength)
             {
                 input = input.Remove(Math.Max(0, input.Length - (newLength - MaxLength)));
             }
-            
+
             if (!string.IsNullOrEmpty(input))
             {
                 DeleteSelection();
@@ -627,7 +643,6 @@ namespace Avalonia.Controls
             SnapshotUndoRedo();
             Copy();
             DeleteSelection();
-            SnapshotUndoRedo();
         }
 
         public async void Copy()
@@ -647,7 +662,6 @@ namespace Avalonia.Controls
 
             SnapshotUndoRedo();
             HandleTextInput(text);
-            SnapshotUndoRedo();
         }
 
         protected override void OnKeyDown(KeyEventArgs e)
@@ -696,6 +710,7 @@ namespace Avalonia.Controls
             {
                 try
                 {
+                    SnapshotUndoRedo();
                     _isUndoingRedoing = true;
                     _undoRedoHelper.Undo();
                 }
@@ -830,7 +845,6 @@ namespace Avalonia.Controls
                             CaretIndex -= removedCharacters;
                             ClearSelection();
                         }
-                        SnapshotUndoRedo();
 
                         handled = true;
                         break;
@@ -858,7 +872,6 @@ namespace Avalonia.Controls
                             SetTextInternal(text.Substring(0, caretIndex) +
                                             text.Substring(caretIndex + removedCharacters));
                         }
-                        SnapshotUndoRedo();
 
                         handled = true;
                         break;
@@ -868,7 +881,6 @@ namespace Avalonia.Controls
                         {
                             SnapshotUndoRedo();
                             HandleTextInput(NewLine);
-                            SnapshotUndoRedo();
                             handled = true;
                         }
 
@@ -879,7 +891,6 @@ namespace Avalonia.Controls
                         {
                             SnapshotUndoRedo();
                             HandleTextInput("\t");
-                            SnapshotUndoRedo();
                             handled = true;
                         }
                         else
@@ -889,6 +900,10 @@ namespace Avalonia.Controls
 
                         break;
 
+                    case Key.Space:
+                        SnapshotUndoRedo(); // always snapshot in between words
+                        break;
+
                     default:
                         handled = false;
                         break;
@@ -1319,11 +1334,19 @@ namespace Avalonia.Controls
             }
         }
 
-        private void SnapshotUndoRedo()
+        private void SnapshotUndoRedo(bool ignoreChangeCount = true)
         {
             if (IsUndoEnabled)
             {
-                _undoRedoHelper.Snapshot();
+                if (ignoreChangeCount ||
+                    !_hasDoneSnapshotOnce ||
+                    (!ignoreChangeCount &&
+                        _selectedTextChangesMadeSinceLastUndoSnapshot >= _maxCharsBeforeUndoSnapshot))
+                {
+                    _undoRedoHelper.Snapshot();
+                    _selectedTextChangesMadeSinceLastUndoSnapshot = 0;
+                    _hasDoneSnapshotOnce = true;
+                }
             }
         }
     }

src/Avalonia.Controls/TickBar.cs

@@ -193,7 +193,7 @@ namespace Avalonia.Controls
 
         /// <summary>
         /// TickBar will use ReservedSpaceProperty for left and right spacing (for horizontal orientation) or
-        /// top and bottom spacing (for vertical orienation).
+        /// top and bottom spacing (for vertical orientation).
         /// The space on both sides of TickBar is half of specified ReservedSpace.
         /// This property has type of <see cref="Rect" />.
         /// </summary>
@@ -210,7 +210,7 @@ namespace Avalonia.Controls
         /// This function also draw selection-tick(s) if IsSelectionRangeEnabled is 'true' and
         /// SelectionStart and SelectionEnd are valid.
         ///
-        /// The primary ticks (for Mininum and Maximum value) height will be 100% of TickBar's render size (use Width or Height
+        /// The primary ticks (for Minimum and Maximum value) height will be 100% of TickBar's render size (use Width or Height
         /// depends on Placement property).
         ///
         /// The secondary ticks (all other ticks, including selection-tics) height will be 75% of TickBar's render size.
@@ -221,7 +221,7 @@ namespace Avalonia.Controls
         {
             var size = new Size(Bounds.Width, Bounds.Height);
             var range = Maximum - Minimum;
-            var tickLen = 0.0d;   // Height for Primary Tick (for Mininum and Maximum value)
+            var tickLen = 0.0d;   // Height for Primary Tick (for Minimum and Maximum value)
             var tickLen2 = 0.0d;  // Height for Secondary Tick
             var logicalToPhysical = 1.0;
             var startPoint = new Point();
@@ -285,7 +285,7 @@ namespace Avalonia.Controls
 
             tickLen2 = tickLen * 0.75;
 
-            // Invert direciton of the ticks
+            // Invert direction of the ticks
             if (IsDirectionReversed)
             {
                 logicalToPhysical *= -1;

src/Avalonia.Controls/ToolTip.cs

@@ -1,9 +1,8 @@
 #nullable enable
 using System;
-using System.Reactive.Linq;
+using Avalonia.Controls.Diagnostics;
 using Avalonia.Controls.Metadata;
 using Avalonia.Controls.Primitives;
-using Avalonia.VisualTree;
 
 namespace Avalonia.Controls
 {
@@ -17,7 +16,7 @@ namespace Avalonia.Controls
     /// assigning the content that you want displayed.
     /// </remarks>
     [PseudoClasses(":open")]
-    public class ToolTip : ContentControl
+    public class ToolTip : ContentControl, IPopupHostProvider
     {
         /// <summary>
         /// Defines the ToolTip.Tip attached property.
@@ -61,7 +60,8 @@ namespace Avalonia.Controls
         internal static readonly AttachedProperty<ToolTip?> ToolTipProperty =
             AvaloniaProperty.RegisterAttached<ToolTip, Control, ToolTip?>("ToolTip");
 
-        private IPopupHost? _popup;
+        private IPopupHost? _popupHost;
+        private Action<IPopupHost?>? _popupHostChangedHandler;
 
         /// <summary>
         /// Initializes static members of the <see cref="ToolTip"/> class.
@@ -251,35 +251,45 @@ namespace Avalonia.Controls
 
             tooltip.RecalculatePosition(control);
         }
+        
+        IPopupHost? IPopupHostProvider.PopupHost => _popupHost;
+
+        event Action<IPopupHost?>? IPopupHostProvider.PopupHostChanged 
+        { 
+            add => _popupHostChangedHandler += value; 
+            remove => _popupHostChangedHandler -= value;
+        }
 
         internal void RecalculatePosition(Control control)
         {
-            _popup?.ConfigurePosition(control, GetPlacement(control), new Point(GetHorizontalOffset(control), GetVerticalOffset(control)));
+            _popupHost?.ConfigurePosition(control, GetPlacement(control), new Point(GetHorizontalOffset(control), GetVerticalOffset(control)));
         }
 
         private void Open(Control control)
         {
             Close();
 
-            _popup = OverlayPopupHost.CreatePopupHost(control, null);
-            _popup.SetChild(this);
-            ((ISetLogicalParent)_popup).SetParent(control);
+            _popupHost = OverlayPopupHost.CreatePopupHost(control, null);
+            _popupHost.SetChild(this);
+            ((ISetLogicalParent)_popupHost).SetParent(control);
             
-            _popup.ConfigurePosition(control, GetPlacement(control), 
+            _popupHost.ConfigurePosition(control, GetPlacement(control), 
                 new Point(GetHorizontalOffset(control), GetVerticalOffset(control)));
 
-            WindowManagerAddShadowHintChanged(_popup, false);
+            WindowManagerAddShadowHintChanged(_popupHost, false);
 
-            _popup.Show();
+            _popupHost.Show();
+            _popupHostChangedHandler?.Invoke(_popupHost);
         }
 
         private void Close()
         {
-            if (_popup != null)
+            if (_popupHost != null)
             {
-                _popup.SetChild(null);
-                _popup.Dispose();
-                _popup = null;
+                _popupHost.SetChild(null);
+                _popupHost.Dispose();
+                _popupHost = null;
+                _popupHostChangedHandler?.Invoke(null);
             }
         }
 

src/Avalonia.Controls/TopLevel.cs

@@ -90,6 +90,7 @@ namespace Avalonia.Controls
         /// </summary>
         static TopLevel()
         {
+            KeyboardNavigation.TabNavigationProperty.OverrideDefaultValue<TopLevel>(KeyboardNavigationMode.Cycle);
             AffectsMeasure<TopLevel>(ClientSizeProperty);
 
             TransparencyLevelHintProperty.Changed.AddClassHandler<TopLevel>(
@@ -224,7 +225,7 @@ namespace Avalonia.Controls
         }
 
         /// <summary>
-        /// Gets the acheived <see cref="WindowTransparencyLevel"/> that the platform was able to provide.
+        /// Gets the achieved <see cref="WindowTransparencyLevel"/> that the platform was able to provide.
         /// </summary>
         public WindowTransparencyLevel ActualTransparencyLevel
         {
@@ -376,11 +377,15 @@ namespace Avalonia.Controls
             LayoutManager?.Dispose();
         }
 
+        [Obsolete("Use HandleResized(Size, PlatformResizeReason)")]
+        protected virtual void HandleResized(Size clientSize) => HandleResized(clientSize, PlatformResizeReason.Unspecified);
+
         /// <summary>
         /// Handles a resize notification from <see cref="ITopLevelImpl.Resized"/>.
         /// </summary>
         /// <param name="clientSize">The new client size.</param>
-        protected virtual void HandleResized(Size clientSize)
+        /// <param name="reason">The reason for the resize.</param>
+        protected virtual void HandleResized(Size clientSize, PlatformResizeReason reason)
         {
             ClientSize = clientSize;
             FrameSize = PlatformImpl.FrameSize;

src/Avalonia.Controls/Utils/UndoRedoHelper.cs

@@ -7,7 +7,7 @@ using Avalonia.Utilities;
 
 namespace Avalonia.Controls.Utils
 {
-    class UndoRedoHelper<TState> : WeakTimer.IWeakTimerSubscriber where TState : struct, IEquatable<TState>
+    class UndoRedoHelper<TState>
     {
         private readonly IUndoRedoHost _host;
 
@@ -31,7 +31,6 @@ namespace Avalonia.Controls.Utils
         public UndoRedoHelper(IUndoRedoHost host)
         {
             _host = host;
-            WeakTimer.StartWeakTimer(this, TimeSpan.FromSeconds(1));
         }
 
         public void Undo()
@@ -61,7 +60,7 @@ namespace Avalonia.Controls.Utils
             if (_states.Last != null)
             {
                 _states.Last.Value = state;
-            } 
+            }
         }
 
         public void UpdateLastState()
@@ -103,11 +102,5 @@ namespace Avalonia.Controls.Utils
             _states.Clear();
             _currentNode = null;
         }
-
-        bool WeakTimer.IWeakTimerSubscriber.Tick()
-        {
-            Snapshot();
-            return true;
-        }
     }
 }

src/Avalonia.Controls/Window.cs

@@ -244,7 +244,7 @@ namespace Avalonia.Controls
             impl.WindowStateChanged = HandleWindowStateChanged;
             _maxPlatformClientSize = PlatformImpl?.MaxAutoSizeHint ?? default(Size);
             impl.ExtendClientAreaToDecorationsChanged = ExtendClientAreaToDecorationsChanged;            
-            this.GetObservable(ClientSizeProperty).Skip(1).Subscribe(x => PlatformImpl?.Resize(x));
+            this.GetObservable(ClientSizeProperty).Skip(1).Subscribe(x => PlatformImpl?.Resize(x, PlatformResizeReason.Application));
 
             PlatformImpl?.ShowTaskbarIcon(ShowInTaskbar);
         }
@@ -258,6 +258,18 @@ namespace Avalonia.Controls
         /// <summary>
         /// Gets or sets a value indicating how the window will size itself to fit its content.
         /// </summary>
+        /// <remarks>
+        /// If <see cref="SizeToContent"/> has a value other than <see cref="SizeToContent.Manual"/>,
+        /// <see cref="SizeToContent"/> is automatically set to <see cref="SizeToContent.Manual"/>
+        /// if a user resizes the window by using the resize grip or dragging the border.
+        /// 
+        /// NOTE: Because of a limitation of X11, <see cref="SizeToContent"/> will be reset on X11 to
+        /// <see cref="SizeToContent.Manual"/> on any resize - including the resize that happens when
+        /// the window is first shown. This is because X11 resize notifications are asynchronous and
+        /// there is no way to know whether a resize came from the user or the layout system. To avoid
+        /// this, consider setting <see cref="CanResize"/> to false, which will disable user resizing
+        /// of the window.
+        /// </remarks>
         public SizeToContent SizeToContent
         {
             get { return GetValue(SizeToContentProperty); }
@@ -583,28 +595,23 @@ namespace Avalonia.Controls
                 return;
             }
 
-            using (BeginAutoSizing())
-            {
-                Renderer?.Stop();
+            Renderer?.Stop();
 
-                if (Owner is Window owner)
-                {
-                    owner.RemoveChild(this);
-                }
+            if (Owner is Window owner)
+            {
+                owner.RemoveChild(this);
+            }
 
-                if (_children.Count > 0)
+            if (_children.Count > 0)
+            {
+                foreach (var child in _children.ToArray())
                 {
-                    foreach (var child in _children.ToArray())
-                    {
-                        child.child.Hide();
-                    }
+                    child.child.Hide();
                 }
-
-                Owner = null;
-
-                PlatformImpl?.Hide();
             }
 
+            Owner = null;
+            PlatformImpl?.Hide();
             IsVisible = false;
         }
 
@@ -675,29 +682,23 @@ namespace Avalonia.Controls
 
             if (initialSize != ClientSize)
             {
-                using (BeginAutoSizing())
-                {
-                    PlatformImpl?.Resize(initialSize);
-                }
+                PlatformImpl?.Resize(initialSize, PlatformResizeReason.Layout);
             }
 
             LayoutManager.ExecuteInitialLayoutPass();
 
-            using (BeginAutoSizing())
+            if (parent != null)
             {
-                if (parent != null)
-                {
-                    PlatformImpl?.SetParent(parent.PlatformImpl);
-                }
-                
-                Owner = parent;
-                parent?.AddChild(this, false);
-                
-                SetWindowStartupLocation(Owner?.PlatformImpl);
-                
-                PlatformImpl?.Show(ShowActivated);
-                Renderer?.Start();                
+                PlatformImpl?.SetParent(parent.PlatformImpl);
             }
+
+            Owner = parent;
+            parent?.AddChild(this, false);
+
+            SetWindowStartupLocation(Owner?.PlatformImpl);
+
+            PlatformImpl?.Show(ShowActivated, false);
+            Renderer?.Start();
             OnOpened(EventArgs.Empty);
         }
 
@@ -760,41 +761,34 @@ namespace Avalonia.Controls
 
             if (initialSize != ClientSize)
             {
-                using (BeginAutoSizing())
-                {
-                    PlatformImpl?.Resize(initialSize);
-                }
+                PlatformImpl?.Resize(initialSize, PlatformResizeReason.Layout);
             }
 
             LayoutManager.ExecuteInitialLayoutPass();
 
             var result = new TaskCompletionSource<TResult>();
 
-            using (BeginAutoSizing())
-            {
-                PlatformImpl?.SetParent(owner.PlatformImpl);
-                Owner = owner;
-                owner.AddChild(this, true);
-                
-                SetWindowStartupLocation(owner.PlatformImpl);
-                
-                PlatformImpl?.Show(ShowActivated);
+            PlatformImpl?.SetParent(owner.PlatformImpl);
+            Owner = owner;
+            owner.AddChild(this, true);
 
-                Renderer?.Start();
+            SetWindowStartupLocation(owner.PlatformImpl);
 
-                Observable.FromEventPattern<EventHandler, EventArgs>(
-                        x => Closed += x,
-                        x => Closed -= x)
-                    .Take(1)
-                    .Subscribe(_ =>
-                    {
-                        owner.Activate();
-                        result.SetResult((TResult)(_dialogResult ?? default(TResult)));
-                    });
+            PlatformImpl?.Show(ShowActivated, true);
 
-                OnOpened(EventArgs.Empty);
-            }
+            Renderer?.Start();
+
+            Observable.FromEventPattern<EventHandler, EventArgs>(
+                    x => Closed += x,
+                    x => Closed -= x)
+                .Take(1)
+                .Subscribe(_ =>
+                {
+                    owner.Activate();
+                    result.SetResult((TResult)(_dialogResult ?? default(TResult)));
+                });
 
+            OnOpened(EventArgs.Empty);
             return result.Task;
         }
 
@@ -937,11 +931,8 @@ namespace Avalonia.Controls
 
         protected sealed override Size ArrangeSetBounds(Size size)
         {
-            using (BeginAutoSizing())
-            {
-                PlatformImpl?.Resize(size);
-                return ClientSize;
-            }
+            PlatformImpl?.Resize(size, PlatformResizeReason.Layout);
+            return ClientSize;
         }
 
         protected sealed override void HandleClosed()
@@ -958,18 +949,36 @@ namespace Avalonia.Controls
             Owner = null;
         }
 
+        [Obsolete("Use HandleResized(Size, PlatformResizeReason)")]
+        protected sealed override void HandleResized(Size clientSize) => HandleResized(clientSize, PlatformResizeReason.Unspecified);
+
         /// <inheritdoc/>
-        protected sealed override void HandleResized(Size clientSize)
+        protected sealed override void HandleResized(Size clientSize, PlatformResizeReason reason)
         {
-            if (!AutoSizing)
+            if (ClientSize == clientSize)
+                return;
+
+            var sizeToContent = SizeToContent;
+
+            // If auto-sizing is enabled, and the resize came from a user resize (or the reason was
+            // unspecified) then turn off auto-resizing for any window dimension that is not equal
+            // to the requested size.
+            if (sizeToContent != SizeToContent.Manual &&
+                CanResize &&
+                reason == PlatformResizeReason.Unspecified ||  
+                reason == PlatformResizeReason.User)
             {
-                SizeToContent = SizeToContent.Manual;
+                if (clientSize.Width != ClientSize.Width)
+                    sizeToContent &= ~SizeToContent.Width;
+                if (clientSize.Height != ClientSize.Height)
+                    sizeToContent &= ~SizeToContent.Height;
+                SizeToContent = sizeToContent;
             }
 
             Width = clientSize.Width;
             Height = clientSize.Height;
 
-            base.HandleResized(clientSize);
+            base.HandleResized(clientSize, reason);
         }
 
         /// <summary>

src/Avalonia.Controls/WindowBase.cs

@@ -39,7 +39,6 @@ namespace Avalonia.Controls
         public static readonly StyledProperty<bool> TopmostProperty =
             AvaloniaProperty.Register<WindowBase, bool>(nameof(Topmost));
 
-        private int _autoSizing;
         private bool _hasExecutedInitialLayoutPass;
         private bool _isActive;
         private bool _ignoreVisibilityChange;
@@ -95,10 +94,8 @@ namespace Avalonia.Controls
         
         public Screens Screens { get; private set; }
 
-        /// <summary>
-        /// Whether an auto-size operation is in progress.
-        /// </summary>
-        protected bool AutoSizing => _autoSizing > 0;
+        [Obsolete("No longer used. Always returns false.")]
+        protected bool AutoSizing => false;
 
         /// <summary>
         /// Gets or sets the owner of the window.
@@ -162,7 +159,7 @@ namespace Avalonia.Controls
                     LayoutManager.ExecuteInitialLayoutPass();
                     _hasExecutedInitialLayoutPass = true;
                 }
-                PlatformImpl?.Show(true);
+                PlatformImpl?.Show(true, false);
                 Renderer?.Start();
                 OnOpened(EventArgs.Empty);
             }
@@ -172,20 +169,9 @@ namespace Avalonia.Controls
             }
         }
 
-        /// <summary>
-        /// Begins an auto-resize operation.
-        /// </summary>
-        /// <returns>A disposable used to finish the operation.</returns>
-        /// <remarks>
-        /// When an auto-resize operation is in progress any resize events received will not be
-        /// cause the new size to be written to the <see cref="Layoutable.Width"/> and
-        /// <see cref="Layoutable.Height"/> properties.
-        /// </remarks>
-        protected IDisposable BeginAutoSizing()
-        {
-            ++_autoSizing;
-            return Disposable.Create(() => --_autoSizing);
-        }
+
+        [Obsolete("No longer used. Has no effect.")]
+        protected IDisposable BeginAutoSizing() => Disposable.Empty;
 
         /// <summary>
         /// Ensures that the window is initialized.
@@ -215,11 +201,15 @@ namespace Avalonia.Controls
             }
         }
 
+        [Obsolete("Use HandleResized(Size, PlatformResizeReason)")]
+        protected override void HandleResized(Size clientSize) => HandleResized(clientSize, PlatformResizeReason.Unspecified);
+
         /// <summary>
         /// Handles a resize notification from <see cref="ITopLevelImpl.Resized"/>.
         /// </summary>
         /// <param name="clientSize">The new client size.</param>
-        protected override void HandleResized(Size clientSize)
+        /// <param name="reason">The reason for the resize.</param>
+        protected override void HandleResized(Size clientSize, PlatformResizeReason reason)
         {
             ClientSize = clientSize;
             FrameSize = PlatformImpl.FrameSize;
@@ -264,7 +254,7 @@ namespace Avalonia.Controls
         }
 
         /// <summary>
-        /// Called durung the arrange pass to set the size of the window.
+        /// Called during the arrange pass to set the size of the window.
         /// </summary>
         /// <param name="size">The requested size of the window.</param>
         /// <returns>The actual size of the window.</returns>

src/Avalonia.DesignerSupport/Remote/PreviewerWindowImpl.cs

@@ -20,7 +20,7 @@ namespace Avalonia.DesignerSupport.Remote
             ClientSize = new Size(1, 1);
         }
 
-        public void Show(bool activate)
+        public void Show(bool activate, bool isDialog)
         {
         }
 
@@ -58,7 +58,7 @@ namespace Avalonia.DesignerSupport.Remote
             base.OnMessage(transport, obj);
         }
         
-        public void Resize(Size clientSize)
+        public void Resize(Size clientSize, PlatformResizeReason reason)
         {
             _transport.Send(new RequestViewportResizeMessage
             {
@@ -99,10 +99,6 @@ namespace Avalonia.DesignerSupport.Remote
         {
         }
 
-        public void ShowDialog(IWindowImpl parent)
-        {
-        }
-
         public void SetSystemDecorations(SystemDecorations enabled)
         {
         }

src/Avalonia.DesignerSupport/Remote/Stubs.cs

@@ -27,7 +27,7 @@ namespace Avalonia.DesignerSupport.Remote
         public IEnumerable<object> Surfaces { get; }
         public Action<RawInputEventArgs> Input { get; set; }
         public Action<Rect> Paint { get; set; }
-        public Action<Size> Resized { get; set; }
+        public Action<Size, PlatformResizeReason> Resized { get; set; }
         public Action<double> ScalingChanged { get; set; }
         public Func<bool> Closing { get; set; }
         public Action Closed { get; set; }
@@ -54,7 +54,7 @@ namespace Avalonia.DesignerSupport.Remote
                 PopupPositioner = new ManagedPopupPositioner(new ManagedPopupPositionerPopupImplHelper(parent,
                     (_, size, __) =>
                     {
-                        Resize(size);
+                        Resize(size, PlatformResizeReason.Unspecified);
                     }));
         }
 
@@ -78,7 +78,7 @@ namespace Avalonia.DesignerSupport.Remote
         {
         }
 
-        public void Show(bool activate)
+        public void Show(bool activate, bool isDialog)
         {
         }
 
@@ -98,7 +98,7 @@ namespace Avalonia.DesignerSupport.Remote
         {
         }
 
-        public void Resize(Size clientSize)
+        public void Resize(Size clientSize, PlatformResizeReason reason)
         {
         }
 

src/Avalonia.Diagnostics/Diagnostics/ViewModels/MainViewModel.cs

@@ -1,6 +1,5 @@
 using System;
 using System.ComponentModel;
-
 using Avalonia.Controls;
 using Avalonia.Diagnostics.Models;
 using Avalonia.Input;
@@ -22,6 +21,7 @@ namespace Avalonia.Diagnostics.ViewModels
         private bool _shouldVisualizeMarginPadding = true;
         private bool _shouldVisualizeDirtyRects;
         private bool _showFpsOverlay;
+        private bool _freezePopups;
         private bool _showPropertyType;
 
 #nullable disable
@@ -42,6 +42,12 @@ namespace Avalonia.Diagnostics.ViewModels
             Console = new ConsoleViewModel(UpdateConsoleContext);
         }
 
+        public bool FreezePopups
+        {
+            get => _freezePopups;
+            set => RaiseAndSetIfChanged(ref _freezePopups, value);
+        }
+
         public bool ShouldVisualizeMarginPadding
         {
             get => _shouldVisualizeMarginPadding;

src/Avalonia.Diagnostics/Diagnostics/ViewModels/TreeNode.cs

@@ -1,26 +1,28 @@
 using System;
-using System.Collections.Generic;
 using System.Collections.Specialized;
 using System.Reactive;
 using System.Reactive.Linq;
 using Avalonia.Controls;
+using Avalonia.Controls.Primitives;
 using Avalonia.LogicalTree;
+using Avalonia.Media;
 using Avalonia.VisualTree;
 
 namespace Avalonia.Diagnostics.ViewModels
 {
     internal abstract class TreeNode : ViewModelBase, IDisposable
     {
-        private IDisposable? _classesSubscription;
+        private readonly IDisposable? _classesSubscription;
         private string _classes;
         private bool _isExpanded;
 
-        public TreeNode(IVisual visual, TreeNode? parent)
+        protected TreeNode(IVisual visual, TreeNode? parent, string? customName = null)
         {
+            _classes = string.Empty;
             Parent = parent;
-            Type = visual.GetType().Name;
+            Type = customName ?? visual.GetType().Name;
             Visual = visual;
-            _classes = string.Empty;
+            FontWeight = IsRoot ? FontWeight.Bold : FontWeight.Normal;
 
             if (visual is IControl control)
             {
@@ -52,6 +54,12 @@ namespace Avalonia.Diagnostics.ViewModels
             }
         }
 
+        private bool IsRoot => Visual is TopLevel ||
+                               Visual is ContextMenu ||
+                               Visual is IPopupHost;
+
+        public FontWeight FontWeight { get; }
+
         public abstract TreeNodeCollection Children
         {
             get;
@@ -95,20 +103,5 @@ namespace Avalonia.Diagnostics.ViewModels
             _classesSubscription?.Dispose();
             Children.Dispose();
         }
-
-        private static int IndexOf(IReadOnlyList<TreeNode> collection, TreeNode item)
-        {
-            var count = collection.Count;
-
-            for (var i = 0; i < count; ++i)
-            {
-                if (collection[i] == item)
-                {
-                    return i;
-                }
-            }
-
-            throw new AvaloniaInternalException("TreeNode was not present in parent Children collection.");
-        }
     }
 }

src/Avalonia.Diagnostics/Diagnostics/ViewModels/VisualTreeNode.cs

@@ -1,5 +1,10 @@
 using System;
+using System.Reactive.Disposables;
+using System.Reactive.Linq;
 using Avalonia.Collections;
+using Avalonia.Controls;
+using Avalonia.Controls.Diagnostics;
+using Avalonia.Controls.Primitives;
 using Avalonia.Styling;
 using Avalonia.VisualTree;
 
@@ -7,31 +12,30 @@ namespace Avalonia.Diagnostics.ViewModels
 {
     internal class VisualTreeNode : TreeNode
     {
-        public VisualTreeNode(IVisual visual, TreeNode? parent)
-            : base(visual, parent)
+        public VisualTreeNode(IVisual visual, TreeNode? parent, string? customName = null)
+            : base(visual, parent, customName)
         {
             Children = new VisualTreeNodeCollection(this, visual);
 
-            if ((Visual is IStyleable styleable))
-            {
+            if (Visual is IStyleable styleable)
                 IsInTemplate = styleable.TemplatedParent != null;
-            }
         }
 
-        public bool IsInTemplate { get; private set; }
+        public bool IsInTemplate { get; }
 
         public override TreeNodeCollection Children { get; }
 
         public static VisualTreeNode[] Create(object control)
         {
-            var visual = control as IVisual;
-            return visual != null ? new[] { new VisualTreeNode(visual, null) } : Array.Empty<VisualTreeNode>();
+            return control is IVisual visual ?
+                new[] { new VisualTreeNode(visual, null) } :
+                Array.Empty<VisualTreeNode>();
         }
 
         internal class VisualTreeNodeCollection : TreeNodeCollection
         {
             private readonly IVisual _control;
-            private IDisposable? _subscription;
+            private readonly CompositeDisposable _subscriptions = new CompositeDisposable(2);
 
             public VisualTreeNodeCollection(TreeNode owner, IVisual control)
                 : base(owner)
@@ -41,15 +45,106 @@ namespace Avalonia.Diagnostics.ViewModels
 
             public override void Dispose()
             {
-                _subscription?.Dispose();
+                _subscriptions.Dispose();
+            }
+
+            private static IObservable<PopupRoot?>? GetHostedPopupRootObservable(IVisual visual)
+            {
+                static IObservable<PopupRoot?> GetPopupHostObservable(
+                    IPopupHostProvider popupHostProvider,
+                    string? providerName = null)
+                {
+                    return Observable.FromEvent<IPopupHost?>(
+                            x => popupHostProvider.PopupHostChanged += x,
+                            x => popupHostProvider.PopupHostChanged -= x)
+                        .StartWith(popupHostProvider.PopupHost)
+                        .Select(popupHost =>
+                        {
+                            if (popupHost is IControl control)
+                                return new PopupRoot(
+                                    control,
+                                    providerName != null ? $"{providerName} ({control.GetType().Name})" : null);
+
+                            return (PopupRoot?)null;
+                        });
+                }
+
+                return visual switch
+                {
+                    Popup p => GetPopupHostObservable(p),
+                    Control c => Observable.CombineLatest(
+                            c.GetObservable(Control.ContextFlyoutProperty),
+                            c.GetObservable(Control.ContextMenuProperty),
+                            c.GetObservable(FlyoutBase.AttachedFlyoutProperty),
+                            c.GetObservable(ToolTipDiagnostics.ToolTipProperty),
+                            (ContextFlyout, ContextMenu, AttachedFlyout, ToolTip) =>
+                            {
+                                if (ContextMenu != null)
+                                    //Note: ContextMenus are special since all the items are added as visual children.
+                                    //So we don't need to go via Popup
+                                    return Observable.Return<PopupRoot?>(new PopupRoot(ContextMenu));
+
+                                if (ContextFlyout != null)
+                                    return GetPopupHostObservable(ContextFlyout, "ContextFlyout");
+
+                                if (AttachedFlyout != null)
+                                    return GetPopupHostObservable(AttachedFlyout, "AttachedFlyout");
+
+                                if (ToolTip != null)
+                                    return GetPopupHostObservable(ToolTip, "ToolTip");
+
+                                return Observable.Return<PopupRoot?>(null);
+                            })
+                        .Switch(),
+                    _ => null
+                };
             }
 
             protected override void Initialize(AvaloniaList<TreeNode> nodes)
             {
-                _subscription = _control.VisualChildren.ForEachItem(
-                    (i, item) => nodes.Insert(i, new VisualTreeNode(item, Owner)),
-                    (i, item) => nodes.RemoveAt(i),
-                    () => nodes.Clear());
+                _subscriptions.Clear();
+
+                if (GetHostedPopupRootObservable(_control) is { } popupRootObservable)
+                {
+                    VisualTreeNode? childNode = null;
+
+                    _subscriptions.Add(
+                        popupRootObservable
+                            .Subscribe(popupRoot =>
+                            {
+                                if (popupRoot != null)
+                                {
+                                    childNode = new VisualTreeNode(
+                                        popupRoot.Value.Root,
+                                        Owner,
+                                        popupRoot.Value.CustomName);
+
+                                    nodes.Add(childNode);
+                                }
+                                else if (childNode != null)
+                                {
+                                    nodes.Remove(childNode);
+                                }
+                            }));
+                }
+
+                _subscriptions.Add(
+                    _control.VisualChildren.ForEachItem(
+                        (i, item) => nodes.Insert(i, new VisualTreeNode(item, Owner)),
+                        (i, item) => nodes.RemoveAt(i),
+                        () => nodes.Clear()));
+            }
+
+            private struct PopupRoot
+            {
+                public PopupRoot(IControl root, string? customName = null)
+                {
+                    Root = root;
+                    CustomName = customName;
+                }
+
+                public IControl Root { get; }
+                public string? CustomName { get; }
             }
         }
     }

src/Avalonia.Diagnostics/Diagnostics/Views/MainView.xaml

@@ -5,14 +5,14 @@
   <Grid Name="rootGrid" RowDefinitions="Auto,Auto,*,Auto,0,Auto">
     <Menu>
       <MenuItem Header="_File">
-        <MenuItem Header="E_xit" Command="{Binding $parent[Window].Close}"/>
+        <MenuItem Header="E_xit" Command="{Binding $parent[Window].Close}" />
       </MenuItem>
       <MenuItem Header="_View">
         <MenuItem Header="_Console" Command="{Binding $parent[UserControl].ToggleConsole}">
           <MenuItem.Icon>
             <CheckBox BorderThickness="0"
                       IsChecked="{Binding Console.IsVisible}"
-                      IsEnabled="False"/>
+                      IsEnabled="False" />
           </MenuItem.Icon>
         </MenuItem>
         <MenuItem Header="_Dettails">
@@ -31,58 +31,68 @@
           <MenuItem.Icon>
             <CheckBox BorderThickness="0"
                       IsChecked="{Binding ShouldVisualizeMarginPadding}"
-                      IsEnabled="False"/>
+                      IsEnabled="False" />
           </MenuItem.Icon>
         </MenuItem>
         <MenuItem Header="Visualize dirty rects" Command="{Binding ToggleVisualizeDirtyRects}">
           <MenuItem.Icon>
             <CheckBox BorderThickness="0"
                       IsChecked="{Binding ShouldVisualizeDirtyRects}"
-                      IsEnabled="False"/>
+                      IsEnabled="False" />
           </MenuItem.Icon>
         </MenuItem>
-         <MenuItem Header="Show fps overlay" Command="{Binding ToggleFpsOverlay}">
+        <MenuItem Header="Show fps overlay" Command="{Binding ToggleFpsOverlay}">
           <MenuItem.Icon>
             <CheckBox BorderThickness="0"
                       IsChecked="{Binding ShowFpsOverlay}"
-                      IsEnabled="False"/>
+                      IsEnabled="False" />
           </MenuItem.Icon>
         </MenuItem>
       </MenuItem>
     </Menu>
-    
+
     <TabStrip Grid.Row="1" SelectedIndex="{Binding SelectedTab, Mode=TwoWay}">
-      <TabStripItem Content="Logical Tree"/>
-      <TabStripItem Content="Visual Tree"/>
-      <TabStripItem Content="Events"/>
+      <TabStripItem Content="Logical Tree" />
+      <TabStripItem Content="Visual Tree" />
+      <TabStripItem Content="Events" />
     </TabStrip>
 
     <ContentControl Grid.Row="2"
                     BorderBrush="{DynamicResource ThemeControlMidBrush}"
                     BorderThickness="0,1,0,0"
-                    Content="{Binding Content}"/>
+                    Content="{Binding Content}" />
 
     <GridSplitter Name="consoleSplitter" Grid.Row="3" Height="1"
                   Background="{DynamicResource ThemeControlMidBrush}"
-                  IsVisible="False"/>
-    
+                  IsVisible="False" />
+
     <views:ConsoleView Name="console"
                        Grid.Row="4"
                        DataContext="{Binding Console}"
-                       IsVisible="{Binding IsVisible}"/>
+                       IsVisible="{Binding IsVisible}" />
+
 
     <Border Grid.Row="5"
             BorderBrush="{DynamicResource ThemeControlMidBrush}"
             BorderThickness="0,1,0,0">
-      <StackPanel Spacing="4" Orientation="Horizontal">
-        <TextBlock>Hold Ctrl+Shift over a control to inspect.</TextBlock>
-        <Separator Width="8"/>
-        <TextBlock>Focused:</TextBlock>
-        <TextBlock Text="{Binding FocusedControl}"/>
-        <Separator Width="8"/>
-        <TextBlock>Pointer Over:</TextBlock>
-        <TextBlock Text="{Binding PointerOverElement}"/>
-      </StackPanel>
+      <Grid ColumnDefinitions="*, Auto">
+        <StackPanel Grid.Column="0" Spacing="4" Orientation="Horizontal">
+          <TextBlock>Hold Ctrl+Shift over a control to inspect.</TextBlock>
+          <Separator Width="8" />
+          <TextBlock>Focused:</TextBlock>
+          <TextBlock Text="{Binding FocusedControl}" />
+          <Separator Width="8" />
+          <TextBlock>Pointer Over:</TextBlock>
+          <TextBlock Text="{Binding PointerOverElement}" />
+        </StackPanel>
+
+        <TextBlock Grid.Column="1"
+                   Foreground="Gray"
+                   Margin="2 0"
+                   Text="Popups frozen"
+                   IsVisible="{Binding FreezePopups}" />
+      </Grid>
+
     </Border>
   </Grid>
 </UserControl>

src/Avalonia.Diagnostics/Diagnostics/Views/MainWindow.xaml.cs

@@ -1,8 +1,11 @@
 using System;
+using System.Collections.Generic;
 using System.Linq;
 using System.Reactive.Linq;
 using Avalonia.Controls;
+using Avalonia.Controls.Diagnostics;
 using Avalonia.Controls.Primitives;
+using Avalonia.Data;
 using Avalonia.Diagnostics.ViewModels;
 using Avalonia.Input;
 using Avalonia.Input.Raw;
@@ -15,6 +18,7 @@ namespace Avalonia.Diagnostics.Views
     internal class MainWindow : Window, IStyleHost
     {
         private readonly IDisposable _keySubscription;
+        private readonly Dictionary<Popup, IDisposable> _frozenPopupStates;
         private TopLevel? _root;
 
         public MainWindow()
@@ -23,23 +27,26 @@ namespace Avalonia.Diagnostics.Views
 
             _keySubscription = InputManager.Instance.Process
                 .OfType<RawKeyEventArgs>()
+                .Where(x => x.Type == RawKeyEventType.KeyDown)
                 .Subscribe(RawKeyDown);
 
+            _frozenPopupStates = new Dictionary<Popup, IDisposable>();
+
             EventHandler? lh = default;
             lh = (s, e) =>
-              {
-                  this.Opened -= lh;
-                  if ((DataContext as MainViewModel)?.StartupScreenIndex is int index)
-                  {
-                      var screens = this.Screens;
-                      if (index > -1 && index < screens.ScreenCount)                          
-                      {
-                          var screen = screens.All[index];
-                          this.Position = screen.Bounds.TopLeft;
-                          this.WindowState = WindowState.Maximized;
-                      }
-                  }
-              };
+            {
+                this.Opened -= lh;
+                if ((DataContext as MainViewModel)?.StartupScreenIndex is { } index)
+                {
+                    var screens = this.Screens;
+                    if (index > -1 && index < screens.ScreenCount)
+                    {
+                        var screen = screens.All[index];
+                        this.Position = screen.Bounds.TopLeft;
+                        this.WindowState = WindowState.Maximized;
+                    }
+                }
+            };
             this.Opened += lh;
         }
 
@@ -77,6 +84,13 @@ namespace Avalonia.Diagnostics.Views
             base.OnClosed(e);
             _keySubscription.Dispose();
 
+            foreach (var state in _frozenPopupStates)
+            {
+                state.Value.Dispose();
+            }
+
+            _frozenPopupStates.Clear();
+
             if (_root != null)
             {
                 _root.Closed -= RootClosed;
@@ -91,6 +105,53 @@ namespace Avalonia.Diagnostics.Views
             AvaloniaXamlLoader.Load(this);
         }
 
+        private IControl? GetHoveredControl(TopLevel topLevel)
+        {
+#pragma warning disable CS0618 // Type or member is obsolete
+            var point = (topLevel as IInputRoot)?.MouseDevice?.GetPosition(topLevel) ?? default;
+#pragma warning restore CS0618 // Type or member is obsolete                
+
+            return (IControl?)topLevel.GetVisualsAt(point, x =>
+                {
+                    if (x is AdornerLayer || !x.IsVisible)
+                    {
+                        return false;
+                    }
+
+                    return !(x is IInputElement ie) || ie.IsHitTestVisible;
+                })
+                .FirstOrDefault();
+        }
+
+        private static List<PopupRoot> GetPopupRoots(IVisual root)
+        {
+            var popupRoots = new List<PopupRoot>();
+
+            void ProcessProperty<T>(IControl control, AvaloniaProperty<T> property)
+            {
+                if (control.GetValue(property) is IPopupHostProvider popupProvider
+                    && popupProvider.PopupHost is PopupRoot popupRoot)
+                {
+                    popupRoots.Add(popupRoot);
+                }
+            }
+
+            foreach (var control in root.GetVisualDescendants().OfType<IControl>())
+            {
+                if (control is Popup p && p.Host is PopupRoot popupRoot)
+                {
+                    popupRoots.Add(popupRoot);
+                }
+
+                ProcessProperty(control, ContextFlyoutProperty);
+                ProcessProperty(control, ContextMenuProperty);
+                ProcessProperty(control, FlyoutBase.AttachedFlyoutProperty);
+                ProcessProperty(control, ToolTipDiagnostics.ToolTipProperty);
+            }
+
+            return popupRoots;
+        }
+
         private void RawKeyDown(RawKeyEventArgs e)
         {
             var vm = (MainViewModel?)DataContext;
@@ -99,34 +160,72 @@ namespace Avalonia.Diagnostics.Views
                 return;
             }
 
-            const RawInputModifiers modifiers = RawInputModifiers.Control | RawInputModifiers.Shift;
-
-            if (e.Modifiers == modifiers)
+            switch (e.Modifiers)
             {
-#pragma warning disable CS0618 // Type or member is obsolete
-                var point = (Root as IInputRoot)?.MouseDevice?.GetPosition(Root) ?? default;
-#pragma warning restore CS0618 // Type or member is obsolete                
+                case RawInputModifiers.Control | RawInputModifiers.Shift:
+                {
+                    IControl? control = null;
+
+                    foreach (var popupRoot in GetPopupRoots(Root))
+                    {
+                        control = GetHoveredControl(popupRoot);
+
+                        if (control != null)
+                        {
+                            break;
+                        }
+                    }
+
+                    control ??= GetHoveredControl(Root);
 
-                var control = Root.GetVisualsAt(point, x =>
+                    if (control != null)
                     {
-                        if (x is AdornerLayer || !x.IsVisible) return false;
-                        if (!(x is IInputElement ie)) return true;
-                        return ie.IsHitTestVisible;
-                    })
-                    .FirstOrDefault();
+                        vm.SelectControl(control);
+                    }
+
+                    break;
+                }
 
-                if (control != null)
+                case RawInputModifiers.Control | RawInputModifiers.Alt when e.Key == Key.F:
                 {
-                    vm.SelectControl((IControl)control);
+                    vm.FreezePopups = !vm.FreezePopups;
+
+                    foreach (var popupRoot in GetPopupRoots(Root))
+                    {
+                        if (popupRoot.Parent is Popup popup)
+                        {
+                            if (vm.FreezePopups)
+                            {
+                                var lightDismissEnabledState = popup.SetValue(
+                                    Popup.IsLightDismissEnabledProperty,
+                                    !vm.FreezePopups,
+                                    BindingPriority.Animation);
+
+                                if (lightDismissEnabledState != null)
+                                {
+                                    _frozenPopupStates[popup] = lightDismissEnabledState;
+                                }
+                            }
+                            else
+                            {
+                                //TODO Use Dictionary.Remove(Key, out Value) in netstandard 2.1
+                                if (_frozenPopupStates.ContainsKey(popup))
+                                {
+                                    _frozenPopupStates[popup].Dispose();
+                                    _frozenPopupStates.Remove(popup);
+                                }
+                            }
+                        }
+                    }
+
+                    break;
                 }
-            } 
-            else if (e.Modifiers == RawInputModifiers.Alt)
-            {
-                if (e.Key == Key.S || e.Key == Key.D)
+
+                case RawInputModifiers.Alt when e.Key == Key.S || e.Key == Key.D:
                 {
-                    var enable = e.Key == Key.S;
+                    vm.EnableSnapshotStyles(e.Key == Key.S);
 
-                    vm.EnableSnapshotStyles(enable);
+                    break;
                 }
             }
         }

src/Avalonia.Diagnostics/Diagnostics/Views/TreePageView.xaml

@@ -11,7 +11,7 @@
         <TreeDataTemplate DataType="vm:TreeNode"
                           ItemsSource="{Binding Children}">
           <StackPanel Orientation="Horizontal" Spacing="8">
-            <TextBlock Text="{Binding Type}"/>
+            <TextBlock Text="{Binding Type}" FontWeight="{Binding FontWeight}"/>
             <TextBlock Text="{Binding Classes}"/>
             <TextBlock Foreground="Gray" Text="{Binding ElementName}"/>
           </StackPanel>

src/Avalonia.Headless/HeadlessWindowImpl.cs

@@ -47,7 +47,7 @@ namespace Avalonia.Headless
         public IEnumerable<object> Surfaces { get; }
         public Action<RawInputEventArgs> Input { get; set; }
         public Action<Rect> Paint { get; set; }
-        public Action<Size> Resized { get; set; }
+        public Action<Size, PlatformResizeReason> Resized { get; set; }
         public Action<double> ScalingChanged { get; set; }
 
         public IRenderer CreateRenderer(IRenderRoot root)
@@ -76,7 +76,7 @@ namespace Avalonia.Headless
         public Action Closed { get; set; }
         public IMouseDevice MouseDevice { get; }
 
-        public void Show(bool activate)
+        public void Show(bool activate, bool isDialog)
         {
             if (activate)
                 Dispatcher.UIThread.Post(() => Activated?.Invoke(), DispatcherPriority.Input);
@@ -108,7 +108,7 @@ namespace Avalonia.Headless
         public Action Activated { get; set; }
         public IPlatformHandle Handle { get; } = new PlatformHandle(IntPtr.Zero, "STUB");
         public Size MaxClientSize { get; } = new Size(1920, 1280);
-        public void Resize(Size clientSize)
+        public void Resize(Size clientSize, PlatformResizeReason reason)
         {
             // Emulate X11 behavior here
             if (IsPopup)
@@ -126,7 +126,7 @@ namespace Avalonia.Headless
             if (ClientSize != clientSize)
             {
                 ClientSize = clientSize;
-                Resized?.Invoke(clientSize);
+                Resized?.Invoke(clientSize, PlatformResizeReason.Unspecified);
             }
         }
 
@@ -148,11 +148,6 @@ namespace Avalonia.Headless
 
         }
 
-        public void ShowDialog(IWindowImpl parent)
-        {
-            Show(true);
-        }
-
         public void SetSystemDecorations(bool enabled)
         {
 

src/Avalonia.Input/Avalonia.Input.csproj

@@ -4,6 +4,9 @@
     <Nullable>Enable</Nullable>
     <WarningsAsErrors>CS8600;CS8602;CS8603</WarningsAsErrors>
   </PropertyGroup>
+  <ItemGroup>
+    <Compile Include="..\Avalonia.Base\Metadata\NullableAttributes.cs" Link="NullableAttributes.cs" />
+  </ItemGroup>
   <ItemGroup>
     <ProjectReference Include="..\Avalonia.Animation\Avalonia.Animation.csproj" />
     <ProjectReference Include="..\Avalonia.Base\Avalonia.Base.csproj" />

src/Avalonia.Input/Cursor.cs

@@ -37,7 +37,7 @@ namespace Avalonia.Input
         BottomSize = BottomSide
 
         // Not available in GTK directly, see http://www.pixelbeat.org/programming/x_cursors/ 
-        // We might enable them later, preferably, by loading pixmax direclty from theme with fallback image
+        // We might enable them later, preferably, by loading pixmax directly from theme with fallback image
         // SizeNorthWestSouthEast,
         // SizeNorthEastSouthWest,
     }

src/Avalonia.Input/FocusManager.cs

@@ -92,6 +92,17 @@ namespace Avalonia.Input
             }
         }
 
+        public IInputElement? GetFocusedElement(IInputElement e)
+        {
+            if (e is IFocusScope scope)
+            {
+                _focusScopes.TryGetValue(scope, out var result);
+                return result;
+            }
+
+            return null;
+        }
+
         /// <summary>
         /// Sets the currently focused element in the specified scope.
         /// </summary>
@@ -151,6 +162,8 @@ namespace Avalonia.Input
             Focus(e);
         }
 
+        public static bool GetIsFocusScope(IInputElement e) => e is IFocusScope;
+
         /// <summary>
         /// Checks if the specified element can be focused.
         /// </summary>

src/Avalonia.Input/GestureRecognizers/ScrollGestureRecognizer.cs

@@ -78,7 +78,7 @@ namespace Avalonia.Input.GestureRecognizers
         // Arbitrary chosen value, probably need to move that to platform settings or something
         private const double ScrollStartDistance = 30;
         
-        // Pixels per second speed that is considered to be the stop of inertiall scroll
+        // Pixels per second speed that is considered to be the stop of inertial scroll
         private const double InertialScrollSpeedEnd = 5;
         
         public void PointerMoved(PointerEventArgs e)

src/Avalonia.Input/ICommandSource.cs

@@ -22,7 +22,7 @@ namespace Avalonia.Input
 
 
         /// <summary>
-        /// Bor the bheavior CanExecuteChanged
+        /// Bor the behavior CanExecuteChanged
         /// </summary>
         /// <param name="sender"></param>
         /// <param name="e"></param>

src/Avalonia.Input/ICustomKeyboardNavigation.cs

@@ -1,4 +1,5 @@
-
+#nullable enable
+
 namespace Avalonia.Input
 {
     /// <summary>
@@ -6,6 +7,18 @@ namespace Avalonia.Input
     /// </summary>
     public interface ICustomKeyboardNavigation
     {
-        (bool handled, IInputElement next) GetNext(IInputElement element, NavigationDirection direction);
+        /// <summary>
+        /// Gets the next element in the specified navigation direction.
+        /// </summary>
+        /// <param name="element">The element being navigated from.</param>
+        /// <param name="direction">The navigation direction.</param>
+        /// <returns>
+        /// A tuple consisting of:
+        /// - A boolean indicating whether the request was handled. If false is returned then 
+        ///   custom navigation will be ignored and default navigation will take place.
+        /// - If handled is true: the next element in the navigation direction, or null if default
+        ///   navigation should continue outside the element.
+        /// </returns>
+        (bool handled, IInputElement? next) GetNext(IInputElement element, NavigationDirection direction);
     }
 }

src/Avalonia.Input/InputElement.cs

@@ -71,6 +71,12 @@ namespace Avalonia.Input
         public static readonly DirectProperty<InputElement, bool> IsPointerOverProperty =
             AvaloniaProperty.RegisterDirect<InputElement, bool>(nameof(IsPointerOver), o => o.IsPointerOver);
 
+        /// <summary>
+        /// Defines the <see cref="IsTabStop"/> property.
+        /// </summary>
+        public static readonly StyledProperty<bool> IsTabStopProperty =
+            KeyboardNavigation.IsTabStopProperty.AddOwner<InputElement>();
+
         /// <summary>
         /// Defines the <see cref="GotFocus"/> event.
         /// </summary>
@@ -99,6 +105,12 @@ namespace Avalonia.Input
                 "KeyUp",
                 RoutingStrategies.Tunnel | RoutingStrategies.Bubble);
 
+        /// <summary>
+        /// Defines the <see cref="TabIndex"/> property.
+        /// </summary>
+        public static readonly StyledProperty<int> TabIndexProperty =
+            KeyboardNavigation.TabIndexProperty.AddOwner<InputElement>();
+
         /// <summary>
         /// Defines the <see cref="TextInput"/> event.
         /// </summary>
@@ -426,6 +438,15 @@ namespace Avalonia.Input
             internal set { SetAndRaise(IsPointerOverProperty, ref _isPointerOver, value); }
         }
 
+        /// <summary>
+        /// Gets or sets a value that indicates whether the control is included in tab navigation.
+        /// </summary>
+        public bool IsTabStop
+        {
+            get => GetValue(IsTabStopProperty);
+            set => SetValue(IsTabStopProperty, value);
+        }
+
         /// <inheritdoc/>
         public bool IsEffectivelyEnabled
         {
@@ -437,6 +458,16 @@ namespace Avalonia.Input
             }
         }
 
+        /// <summary>
+        /// Gets or sets a value that determines the order in which elements receive focus when the
+        /// user navigates through controls by pressing the Tab key.
+        /// </summary>
+        public int TabIndex
+        {
+            get => GetValue(TabIndexProperty);
+            set => SetValue(TabIndexProperty, value);
+        }
+
         public List<KeyBinding> KeyBindings { get; } = new List<KeyBinding>();
 
         /// <summary>

src/Avalonia.Input/KeyboardNavigation.cs

@@ -5,6 +5,15 @@ namespace Avalonia.Input
     /// </summary>
     public static class KeyboardNavigation
     {
+        /// <summary>
+        /// Defines the TabIndex attached property.
+        /// </summary>
+        public static readonly AttachedProperty<int> TabIndexProperty =
+            AvaloniaProperty.RegisterAttached<StyledElement, int>(
+                "TabIndex",
+                typeof(KeyboardNavigation),
+                int.MaxValue);
+
         /// <summary>
         /// Defines the TabNavigation attached property.
         /// </summary>
@@ -42,6 +51,26 @@ namespace Avalonia.Input
                 typeof(KeyboardNavigation), 
                 true);
 
+        /// <summary>
+        /// Gets the <see cref="TabIndexProperty"/> for an element.
+        /// </summary>
+        /// <param name="element">The container.</param>
+        /// <returns>The <see cref="KeyboardNavigationMode"/> for the container.</returns>
+        public static int GetTabIndex(IInputElement element)
+        {
+            return ((IAvaloniaObject)element).GetValue(TabIndexProperty);
+        }
+
+        /// <summary>
+        /// Sets the <see cref="TabIndexProperty"/> for an element.
+        /// </summary>
+        /// <param name="element">The element.</param>
+        /// <param name="value">The tab index.</param>
+        public static void SetTabIndex(IInputElement element, int value)
+        {
+            ((IAvaloniaObject)element).SetValue(TabIndexProperty, value);
+        }
+
         /// <summary>
         /// Gets the <see cref="TabNavigationProperty"/> for a container.
         /// </summary>
@@ -83,7 +112,7 @@ namespace Avalonia.Input
         }
 
         /// <summary>
-        /// Sets the <see cref="IsTabStopProperty"/> for a container.
+        /// Sets the <see cref="IsTabStopProperty"/> for an element.
         /// </summary>
         /// <param name="element">The container.</param>
         /// <param name="value">Value indicating whether the container is a tab stop.</param>
@@ -93,7 +122,7 @@ namespace Avalonia.Input
         }
 
         /// <summary>
-        /// Gets the <see cref="IsTabStopProperty"/> for a container.
+        /// Gets the <see cref="IsTabStopProperty"/> for an element.
         /// </summary>
         /// <param name="element">The container.</param>
         /// <returns>Whether the container is a tab stop.</returns>

src/Avalonia.Input/KeyboardNavigationHandler.cs

@@ -1,4 +1,5 @@
 using System;
+using System.Diagnostics.CodeAnalysis;
 using System.Linq;
 using Avalonia.Input.Navigation;
 using Avalonia.VisualTree;
@@ -48,39 +49,24 @@ namespace Avalonia.Input
         {
             element = element ?? throw new ArgumentNullException(nameof(element));
 
-            var customHandler = element.GetSelfAndVisualAncestors()
-                .OfType<ICustomKeyboardNavigation>()
-                .FirstOrDefault();
+            // If there's a custom keyboard navigation handler as an ancestor, use that.
+            var custom = element.FindAncestorOfType<ICustomKeyboardNavigation>(true);
+            if (custom is object && HandlePreCustomNavigation(custom, element, direction, out var ce))
+                return ce;
 
-            if (customHandler != null)
+            var result = direction switch
             {
-                var (handled, next) = customHandler.GetNext(element, direction);
+                NavigationDirection.Next => TabNavigation.GetNextTab(element, false),
+                NavigationDirection.Previous => TabNavigation.GetPrevTab(element, null, false),
+                _ => throw new NotSupportedException(),
+            };
 
-                if (handled)
-                {
-                    if (next != null)
-                    {
-                        return next;
-                    }
-                    else if (direction == NavigationDirection.Next || direction == NavigationDirection.Previous)
-                    {
-                        return TabNavigation.GetNextInTabOrder((IInputElement)customHandler, direction, true);
-                    }
-                    else
-                    {
-                        return null;
-                    }
-                }
-            }
+            // If there wasn't a custom navigation handler as an ancestor of the current element,
+            // but there is one as an ancestor of the new element, use that.
+            if (custom is null && HandlePostCustomNavigation(element, result, direction, out ce))
+                return ce;
 
-            if (direction == NavigationDirection.Next || direction == NavigationDirection.Previous)
-            {
-                return TabNavigation.GetNextInTabOrder(element, direction);
-            }
-            else
-            {
-                throw new NotSupportedException();
-            }
+            return result;
         }
 
         /// <summary>
@@ -90,7 +76,7 @@ namespace Avalonia.Input
         /// <param name="direction">The direction to move.</param>
         /// <param name="keyModifiers">Any key modifiers active at the time of focus.</param>
         public void Move(
-            IInputElement element, 
+            IInputElement element,
             NavigationDirection direction,
             KeyModifiers keyModifiers = KeyModifiers.None)
         {
@@ -124,5 +110,70 @@ namespace Avalonia.Input
                 e.Handled = true;
             }
         }
+
+        private static bool HandlePreCustomNavigation(
+            ICustomKeyboardNavigation customHandler,
+            IInputElement element,
+            NavigationDirection direction,
+            [NotNullWhen(true)] out IInputElement? result)
+        {
+            if (customHandler != null)
+            {
+                var (handled, next) = customHandler.GetNext(element, direction);
+
+                if (handled)
+                {
+                    if (next != null)
+                    {
+                        result = next;
+                        return true;
+                    }
+                    else if (direction == NavigationDirection.Next || direction == NavigationDirection.Previous)
+                    {
+                        var r = direction switch
+                        {
+                            NavigationDirection.Next => TabNavigation.GetNextTabOutside(customHandler),
+                            NavigationDirection.Previous => TabNavigation.GetPrevTabOutside(customHandler),
+                            _ => throw new NotSupportedException(),
+                        };
+
+                        if (r is object)
+                        {
+                            result = r;
+                            return true;
+                        }
+                    }
+                }
+            }
+
+            result = null;
+            return false;
+        }
+
+        private static bool HandlePostCustomNavigation(
+            IInputElement element,
+            IInputElement? newElement,
+            NavigationDirection direction,
+            [NotNullWhen(true)] out IInputElement? result)
+        {
+            if (newElement is object)
+            {
+                var customHandler = newElement.FindAncestorOfType<ICustomKeyboardNavigation>(true);
+
+                if (customHandler is object)
+                {
+                    var (handled, next) = customHandler.GetNext(element, direction);
+
+                    if (handled && next is object)
+                    {
+                        result = next;
+                        return true;
+                    }
+                }
+            }
+
+            result = null;
+            return false;
+        }
     }
 }

src/Avalonia.Input/KeyboardNavigationMode.cs

@@ -36,5 +36,10 @@ namespace Avalonia.Input
         /// The container's children will not be focused when using the tab key.
         /// </summary>
         None,
+
+        /// <summary>
+        /// TabIndexes are considered on local subtree only inside this container
+        /// </summary>
+        Local,
     }
-}
+}

src/Avalonia.Input/Navigation/TabNavigation.cs

@@ -10,277 +10,663 @@ namespace Avalonia.Input.Navigation
     /// </summary>
     internal static class TabNavigation
     {
-        /// <summary>
-        /// Gets the next control in the specified tab direction.
-        /// </summary>
-        /// <param name="element">The element.</param>
-        /// <param name="direction">The tab direction. Must be Next or Previous.</param>
-        /// <param name="outsideElement">
-        /// If true will not descend into <paramref name="element"/> to find next control.
-        /// </param>
-        /// <returns>
-        /// The next element in the specified direction, or null if <paramref name="element"/>
-        /// was the last in the requested direction.
-        /// </returns>
-        public static IInputElement? GetNextInTabOrder(
-            IInputElement element,
-            NavigationDirection direction,
-            bool outsideElement = false)
+        public static IInputElement? GetNextTab(IInputElement e, bool goDownOnly)
         {
-            element = element ?? throw new ArgumentNullException(nameof(element));
-
-            if (direction != NavigationDirection.Next && direction != NavigationDirection.Previous)
-            {
-                throw new ArgumentException("Invalid direction: must be Next or Previous.");
-            }
+            return GetNextTab(e, GetGroupParent(e), goDownOnly);
+        }
 
-            var container = element.GetVisualParent<IInputElement>();
+        public static IInputElement? GetNextTab(IInputElement? e, IInputElement container, bool goDownOnly)
+        {
+            var tabbingType = GetKeyNavigationMode(container);
 
-            if (container != null)
+            if (e == null)
             {
-                var mode = KeyboardNavigation.GetTabNavigation((InputElement)container);
+                if (IsTabStop(container))
+                    return container;
 
-                switch (mode)
+                // Using ActiveElement if set
+                var activeElement = GetActiveElement(container);
+                if (activeElement != null)
+                    return GetNextTab(null, activeElement, true);
+            }
+            else
+            {
+                if (tabbingType == KeyboardNavigationMode.Once || tabbingType == KeyboardNavigationMode.None)
                 {
-                    case KeyboardNavigationMode.Continue:
-                        return GetNextInContainer(element, container, direction, outsideElement) ??
-                               GetFirstInNextContainer(element, element, direction);
-                    case KeyboardNavigationMode.Cycle:
-                        return GetNextInContainer(element, container, direction, outsideElement) ??
-                               GetFocusableDescendant(container, direction);
-                    case KeyboardNavigationMode.Contained:
-                        return GetNextInContainer(element, container, direction, outsideElement);
-                    default:
-                        return GetFirstInNextContainer(element, container, direction);
+                    if (container != e)
+                    {
+                        if (goDownOnly)
+                            return null;
+                        var parentContainer = GetGroupParent(container);
+                        return GetNextTab(container, parentContainer, goDownOnly);
+                    }
                 }
             }
-            else
+
+            // All groups
+            IInputElement? loopStartElement = null;
+            var nextTabElement = e;
+            var currentTabbingType = tabbingType;
+
+            // Search down inside the container
+            while ((nextTabElement = GetNextTabInGroup(nextTabElement, container, currentTabbingType)) != null)
             {
-                return GetFocusableDescendants(element, direction).FirstOrDefault();
+                // Avoid the endless loop here for Cycle groups
+                if (loopStartElement == nextTabElement)
+                    break;
+                if (loopStartElement == null)
+                    loopStartElement = nextTabElement;
+
+                var firstTabElementInside = GetNextTab(null, nextTabElement, true);
+                if (firstTabElementInside != null)
+                    return firstTabElementInside;
+
+                // If we want to continue searching inside the Once groups, we should change the navigation mode
+                if (currentTabbingType == KeyboardNavigationMode.Once)
+                    currentTabbingType = KeyboardNavigationMode.Contained;
             }
+
+            // If there is no next element in the group (nextTabElement == null)
+
+            // Search up in the tree if allowed
+            // consider: Use original tabbingType instead of currentTabbingType
+            if (!goDownOnly && currentTabbingType != KeyboardNavigationMode.Contained && GetParent(container) != null)
+            {
+                return GetNextTab(container, GetGroupParent(container), false);
+            }
+
+            return null;
         }
 
-        /// <summary>
-        /// Gets the first or last focusable descendant of the specified element.
-        /// </summary>
-        /// <param name="container">The element.</param>
-        /// <param name="direction">The direction to search.</param>
-        /// <returns>The element or null if not found.##</returns>
-        private static IInputElement GetFocusableDescendant(IInputElement container, NavigationDirection direction)
+        public static IInputElement? GetNextTabOutside(ICustomKeyboardNavigation e)
         {
-            return direction == NavigationDirection.Next ?
-                GetFocusableDescendants(container, direction).FirstOrDefault() :
-                GetFocusableDescendants(container, direction).LastOrDefault();
+            if (e is IInputElement container)
+            {
+                var last = GetLastInTree(container);
+
+                if (last is object)
+                    return GetNextTab(last, false);
+            }
+
+            return null;
         }
 
-        /// <summary>
-        /// Gets the focusable descendants of the specified element.
-        /// </summary>
-        /// <param name="element">The element.</param>
-        /// <param name="direction">The tab direction. Must be Next or Previous.</param>
-        /// <returns>The element's focusable descendants.</returns>
-        private static IEnumerable<IInputElement> GetFocusableDescendants(IInputElement element,
-            NavigationDirection direction)
+        public static IInputElement? GetPrevTab(IInputElement? e, IInputElement? container, bool goDownOnly)
         {
-            var mode = KeyboardNavigation.GetTabNavigation((InputElement)element);
+            if (e is null && container is null)
+                throw new InvalidOperationException("Either 'e' or 'container' must be non-null.");
 
-            if (mode == KeyboardNavigationMode.None)
-            {
-                yield break;
-            }
+            if (container is null)
+                container = GetGroupParent(e!);
 
-            var children = element.GetVisualChildren().OfType<IInputElement>();
+            KeyboardNavigationMode tabbingType = GetKeyNavigationMode(container);
 
-            if (mode == KeyboardNavigationMode.Once)
+            if (e == null)
             {
-                var active = KeyboardNavigation.GetTabOnceActiveElement((InputElement)element);
-
-                if (active != null)
+                // Using ActiveElement if set
+                var activeElement = GetActiveElement(container);
+                if (activeElement != null)
+                    return GetPrevTab(null, activeElement, true);
+                else
                 {
-                    yield return active;
-                    yield break;
+                    // If we Shift+Tab on a container with KeyboardNavigationMode=Once, and ActiveElement is null
+                    // then we want to go to the first item (not last) within the container
+                    if (tabbingType == KeyboardNavigationMode.Once)
+                    {
+                        var firstTabElement = GetNextTabInGroup(null, container, tabbingType);
+                        if (firstTabElement == null)
+                        {
+                            if (IsTabStop(container))
+                                return container;
+                            if (goDownOnly)
+                                return null;
+
+                            return GetPrevTab(container, null, false);
+                        }
+                        else
+                        {
+                            return GetPrevTab(null, firstTabElement, true);
+                        }
+                    }
                 }
-                else
+            }
+            else
+            {
+                if (tabbingType == KeyboardNavigationMode.Once || tabbingType == KeyboardNavigationMode.None)
                 {
-                    children = children.Take(1);
+                    if (goDownOnly || container == e)
+                        return null;
+
+                    // FocusedElement should not be e otherwise we will delegate focus to the same element
+                    if (IsTabStop(container))
+                        return container;
+
+                    return GetPrevTab(container, null, false);
                 }
             }
 
-            foreach (var child in children)
+            // All groups (except Once) - continue
+            IInputElement? loopStartElement = null;
+            IInputElement? nextTabElement = e;
+
+            // Look for element with the same TabIndex before the current element
+            while ((nextTabElement = GetPrevTabInGroup(nextTabElement, container, tabbingType)) != null)
             {
-                var customNext = GetCustomNext(child, direction);
+                if (nextTabElement == container && tabbingType == KeyboardNavigationMode.Local)
+                    break;
+
+                // At this point nextTabElement is TabStop or TabGroup
+                // In case it is a TabStop only return the element
+                if (IsTabStop(nextTabElement) && !IsGroup(nextTabElement))
+                    return nextTabElement;
+
+                // Avoid the endless loop here
+                if (loopStartElement == nextTabElement)
+                    break;
+                if (loopStartElement == null)
+                    loopStartElement = nextTabElement;
+
+                // At this point nextTabElement is TabGroup
+                var lastTabElementInside = GetPrevTab(null, nextTabElement, true);
+                if (lastTabElementInside != null)
+                    return lastTabElementInside;
+            }
 
-                if (customNext.handled)
-                {
-                    yield return customNext.next!;
-                }
-                else
+            if (tabbingType == KeyboardNavigationMode.Contained)
+                return null;
+
+            if (e != container && IsTabStop(container))
+                return container;
+
+            // If end of the subtree is reached or there no other elements above
+            if (!goDownOnly && GetParent(container) != null)
+            {
+                return GetPrevTab(container, null, false);
+            }
+
+            return null;
+        }
+
+        public static IInputElement? GetPrevTabOutside(ICustomKeyboardNavigation e)
+        {
+            if (e is IInputElement container)
+            {
+                var first = GetFirstChild(container);
+
+                if (first is object)
+                    return GetPrevTab(first, null, false);
+            }
+
+            return null;
+        }
+
+        private static IInputElement? FocusedElement(IInputElement e)
+        {
+            var iie = e;
+            // Focus delegation is enabled only if keyboard focus is outside the container
+            if (iie != null && !iie.IsKeyboardFocusWithin)
+            {
+                var focusedElement = (FocusManager.Instance as FocusManager)?.GetFocusedElement(e);
+                if (focusedElement != null)
                 {
-                    if (child.CanFocus() && KeyboardNavigation.GetIsTabStop((InputElement)child))
+                    if (!IsFocusScope(e))
                     {
-                        yield return child;
+                        // Verify if focusedElement is a visual descendant of e
+                        if (focusedElement is IVisual visualFocusedElement &&
+                            visualFocusedElement != e &&
+                            e.IsVisualAncestorOf(visualFocusedElement))
+                        {
+                            return focusedElement;
+                        }
                     }
+                }
+            }
+
+            return null;
+        }
+
+        private static IInputElement? GetFirstChild(IInputElement e)
+        {
+            // If the element has a FocusedElement it should be its first child
+            if (FocusedElement(e) is IInputElement focusedElement)
+                return focusedElement;
 
-                    if (child.CanFocusDescendants())
+            // Return the first visible element.
+            var uiElement = e as InputElement;
+
+            if (uiElement is null || uiElement.IsVisible)
+            {
+                if (e is IVisual elementAsVisual)
+                {
+                    var children = elementAsVisual.VisualChildren;
+                    var count = children.Count;
+
+                    for (int i = 0; i < count; i++)
                     {
-                        foreach (var descendant in GetFocusableDescendants(child, direction))
+                        if (children[i] is InputElement ie)
                         {
-                            if (KeyboardNavigation.GetIsTabStop((InputElement)descendant))
+                            if (ie.IsVisible)
+                                return ie;
+                            else
                             {
-                                yield return descendant;
+                                var firstChild = GetFirstChild(ie);
+                                if (firstChild != null)
+                                    return firstChild;
                             }
                         }
                     }
                 }
             }
+
+            return null;
         }
 
-        /// <summary>
-        /// Gets the next item that should be focused in the specified container.
-        /// </summary>
-        /// <param name="element">The starting element/</param>
-        /// <param name="container">The container.</param>
-        /// <param name="direction">The direction.</param>
-        /// <param name="outsideElement">
-        /// If true will not descend into <paramref name="element"/> to find next control.
-        /// </param>
-        /// <returns>The next element, or null if the element is the last.</returns>
-        private static IInputElement? GetNextInContainer(
-            IInputElement element,
-            IInputElement container,
-            NavigationDirection direction,
-            bool outsideElement)
+        private static IInputElement? GetLastChild(IInputElement e)
         {
-            IInputElement? e = element;
+            // If the element has a FocusedElement it should be its last child
+            if (FocusedElement(e) is IInputElement focusedElement)
+                return focusedElement;
 
-            if (direction == NavigationDirection.Next && !outsideElement)
-            {
-                var descendant = GetFocusableDescendants(element, direction).FirstOrDefault();
+            // Return the last visible element.
+            var uiElement = e as InputElement;
 
-                if (descendant != null)
-                {
-                    return descendant;
-                }
-            }
-
-            if (container != null)
+            if (uiElement == null || uiElement.IsVisible)
             {
-                var navigable = container as INavigableContainer;
+                var elementAsVisual = e as IVisual;
 
-                // TODO: Do a spatial search here if the container doesn't implement
-                // INavigableContainer.
-                if (navigable != null)
+                if (elementAsVisual != null)
                 {
-                    while (e != null)
-                    {
-                        e = navigable.GetControl(direction, e, false);
+                    var children = elementAsVisual.VisualChildren;
+                    var count = children.Count;
 
-                        if (e != null && 
-                            e.CanFocus() &&
-                            KeyboardNavigation.GetIsTabStop((InputElement)e))
+                    for (int i = count - 1; i >= 0; i--)
+                    {
+                        if (children[i] is InputElement ie)
                         {
-                            break;
+                            if (ie.IsVisible)
+                                return ie;
+                            else
+                            {
+                                var lastChild = GetLastChild(ie);
+                                if (lastChild != null)
+                                    return lastChild;
+                            }
                         }
                     }
                 }
-                else
+            }
+
+            return null;
+        }
+
+        private static IInputElement? GetFirstTabInGroup(IInputElement container)
+        {
+            IInputElement? firstTabElement = null;
+            int minIndexFirstTab = int.MinValue;
+
+            var currElement = container;
+            while ((currElement = GetNextInTree(currElement, container)) != null)
+            {
+                if (IsTabStopOrGroup(currElement))
                 {
-                    // TODO: Do a spatial search here if the container doesn't implement
-                    // INavigableContainer.
-                    e = null;
+                    int currPriority = KeyboardNavigation.GetTabIndex(currElement);
+
+                    if (currPriority < minIndexFirstTab || firstTabElement == null)
+                    {
+                        minIndexFirstTab = currPriority;
+                        firstTabElement = currElement;
+                    }
                 }
+            }
+            return firstTabElement;
+        }
+
+        private static IInputElement? GetLastInTree(IInputElement container)
+        {
+            IInputElement? result;
+            IInputElement? c = container;
+
+            do
+            {
+                result = c;
+                c = GetLastChild(c);
+            } while (c != null && !IsGroup(c));
+
+            if (c != null)
+                return c;
+
+            return result;
+        }
 
-                if (e != null && direction == NavigationDirection.Previous)
+        private static IInputElement? GetLastTabInGroup(IInputElement container)
+        {
+            IInputElement? lastTabElement = null;
+            int maxIndexFirstTab = int.MaxValue;
+            var currElement = GetLastInTree(container);
+            while (currElement != null && currElement != container)
+            {
+                if (IsTabStopOrGroup(currElement))
                 {
-                    var descendant = GetFocusableDescendants(e, direction).LastOrDefault();
+                    int currPriority = KeyboardNavigation.GetTabIndex(currElement);
 
-                    if (descendant != null)
+                    if (currPriority > maxIndexFirstTab || lastTabElement == null)
                     {
-                        return descendant;
+                        maxIndexFirstTab = currPriority;
+                        lastTabElement = currElement;
                     }
                 }
+                currElement = GetPreviousInTree(currElement, container);
+            }
+            return lastTabElement;
+        }
+
+        private static IInputElement? GetNextInTree(IInputElement e, IInputElement container)
+        {
+            IInputElement? result = null;
+
+            if (e == container || !IsGroup(e))
+                result = GetFirstChild(e);
+
+            if (result != null || e == container)
+                return result;
+
+            IInputElement? parent = e;
+            do
+            {
+                var sibling = GetNextSibling(parent);
+                if (sibling != null)
+                    return sibling;
 
-                return e;
+                parent = GetParent(parent);
+            } while (parent != null && parent != container);
+
+            return null;
+        }
+
+        private static IInputElement? GetNextSibling(IInputElement e)
+        {
+            if (GetParent(e) is IVisual parentAsVisual && e is IVisual elementAsVisual)
+            {
+                var children = parentAsVisual.VisualChildren;
+                var count = children.Count;
+                var i = 0;
+
+                //go till itself
+                for (; i < count; i++)
+                {
+                    var vchild = children[i];
+                    if (vchild == elementAsVisual)
+                        break;
+                }
+                i++;
+                //search ahead
+                for (; i < count; i++)
+                {
+                    var visual = children[i];
+                    if (visual is IInputElement ie)
+                        return ie;
+                }
             }
 
             return null;
         }
 
-        /// <summary>
-        /// Gets the first item that should be focused in the next container.
-        /// </summary>
-        /// <param name="element">The element being navigated away from.</param>
-        /// <param name="container">The container.</param>
-        /// <param name="direction">The direction of the search.</param>
-        /// <returns>The first element, or null if there are no more elements.</returns>
-        private static IInputElement? GetFirstInNextContainer(
-            IInputElement element,
-            IInputElement container,
-            NavigationDirection direction)
+        private static IInputElement? GetNextTabInGroup(IInputElement? e, IInputElement container, KeyboardNavigationMode tabbingType)
         {
-            var parent = container.GetVisualParent<IInputElement>();
-            IInputElement? next = null;
+            // None groups: Tab navigation is not supported
+            if (tabbingType == KeyboardNavigationMode.None)
+                return null;
 
-            if (parent != null)
+            // e == null or e == container -> return the first TabStopOrGroup
+            if (e == null || e == container)
             {
-                if (direction == NavigationDirection.Previous &&
-                    parent.CanFocus() && 
-                    KeyboardNavigation.GetIsTabStop((InputElement) parent))
+                return GetFirstTabInGroup(container);
+            }
+
+            if (tabbingType == KeyboardNavigationMode.Once)
+                return null;
+
+            var nextTabElement = GetNextTabWithSameIndex(e, container);
+            if (nextTabElement != null)
+                return nextTabElement;
+
+            return GetNextTabWithNextIndex(e, container, tabbingType);
+        }
+
+        private static IInputElement? GetNextTabWithSameIndex(IInputElement e, IInputElement container)
+        {
+            var elementTabPriority = KeyboardNavigation.GetTabIndex(e);
+            var currElement = e;
+            while ((currElement = GetNextInTree(currElement, container)) != null)
+            {
+                if (IsTabStopOrGroup(currElement) && KeyboardNavigation.GetTabIndex(currElement) == elementTabPriority)
                 {
-                    return parent;
+                    return currElement;
                 }
+            }
 
-                var allSiblings = parent.GetVisualChildren()
-                    .OfType<IInputElement>()
-                    .Where(FocusExtensions.CanFocusDescendants);
-                var siblings = direction == NavigationDirection.Next ?
-                    allSiblings.SkipWhile(x => x != container).Skip(1) :
-                    allSiblings.TakeWhile(x => x != container).Reverse();
+            return null;
+        }
 
-                foreach (var sibling in siblings)
+        private static IInputElement? GetNextTabWithNextIndex(IInputElement e, IInputElement container, KeyboardNavigationMode tabbingType)
+        {
+            // Find the next min index in the tree
+            // min (index>currentTabIndex)
+            IInputElement? nextTabElement = null;
+            IInputElement? firstTabElement = null;
+            int minIndexFirstTab = int.MinValue;
+            int minIndex = int.MinValue;
+            int elementTabPriority = KeyboardNavigation.GetTabIndex(e);
+
+            IInputElement? currElement = container;
+            while ((currElement = GetNextInTree(currElement, container)) != null)
+            {
+                if (IsTabStopOrGroup(currElement))
                 {
-                    var customNext = GetCustomNext(sibling, direction);
-                    if (customNext.handled)
+                    int currPriority = KeyboardNavigation.GetTabIndex(currElement);
+                    if (currPriority > elementTabPriority)
                     {
-                        return customNext.next;
+                        if (currPriority < minIndex || nextTabElement == null)
+                        {
+                            minIndex = currPriority;
+                            nextTabElement = currElement;
+                        }
                     }
 
-                    if (sibling.CanFocus() && KeyboardNavigation.GetIsTabStop((InputElement) sibling))
+                    if (currPriority < minIndexFirstTab || firstTabElement == null)
                     {
-                        return sibling;
+                        minIndexFirstTab = currPriority;
+                        firstTabElement = currElement;
                     }
+                }
+            }
 
-                    next = direction == NavigationDirection.Next ?
-                        GetFocusableDescendants(sibling, direction).FirstOrDefault() :
-                        GetFocusableDescendants(sibling, direction).LastOrDefault();
+            // Cycle groups: if not found - return first element
+            if (tabbingType == KeyboardNavigationMode.Cycle && nextTabElement == null)
+                nextTabElement = firstTabElement;
+
+            return nextTabElement;
+        }
 
-                    if (next != null)
+        private static IInputElement? GetPrevTabInGroup(IInputElement? e, IInputElement container, KeyboardNavigationMode tabbingType)
+        {
+            // None groups: Tab navigation is not supported
+            if (tabbingType == KeyboardNavigationMode.None)
+                return null;
+
+            // Search the last index inside the group
+            if (e == null)
+            {
+                return GetLastTabInGroup(container);
+            }
+
+            if (tabbingType == KeyboardNavigationMode.Once)
+                return null;
+
+            if (e == container)
+                return null;
+
+            var nextTabElement = GetPrevTabWithSameIndex(e, container);
+            if (nextTabElement != null)
+                return nextTabElement;
+
+            return GetPrevTabWithPrevIndex(e, container, tabbingType);
+        }
+
+        private static IInputElement? GetPrevTabWithSameIndex(IInputElement e, IInputElement container)
+        {
+            int elementTabPriority = KeyboardNavigation.GetTabIndex(e);
+            var currElement = GetPreviousInTree(e, container);
+            while (currElement != null)
+            {
+                if (IsTabStopOrGroup(currElement) && KeyboardNavigation.GetTabIndex(currElement) == elementTabPriority && currElement != container)
+                {
+                    return currElement;
+                }
+                currElement = GetPreviousInTree(currElement, container);
+            }
+            return null;
+        }
+
+        private static IInputElement? GetPrevTabWithPrevIndex(IInputElement e, IInputElement container, KeyboardNavigationMode tabbingType)
+        {
+            // Find the next max index in the tree
+            // max (index<currentTabIndex)
+            IInputElement? lastTabElement = null;
+            IInputElement? nextTabElement = null;
+            int elementTabPriority = KeyboardNavigation.GetTabIndex(e);
+            int maxIndexFirstTab = Int32.MaxValue;
+            int maxIndex = Int32.MaxValue;
+            var currElement = GetLastInTree(container);
+            while (currElement != null)
+            {
+                if (IsTabStopOrGroup(currElement) && currElement != container)
+                {
+                    int currPriority = KeyboardNavigation.GetTabIndex(currElement);
+                    if (currPriority < elementTabPriority)
+                    {
+                        if (currPriority > maxIndex || nextTabElement == null)
+                        {
+                            maxIndex = currPriority;
+                            nextTabElement = currElement;
+                        }
+                    }
+
+                    if (currPriority > maxIndexFirstTab || lastTabElement == null)
                     {
-                        return next;
+                        maxIndexFirstTab = currPriority;
+                        lastTabElement = currElement;
                     }
                 }
 
-                next = GetFirstInNextContainer(element, parent, direction);
+                currElement = GetPreviousInTree(currElement, container);
+            }
+
+            // Cycle groups: if not found - return first element
+            if (tabbingType == KeyboardNavigationMode.Cycle && nextTabElement == null)
+                nextTabElement = lastTabElement;
+
+            return nextTabElement;
+        }
+
+        private static IInputElement? GetPreviousInTree(IInputElement e, IInputElement container)
+        {
+            if (e == container)
+                return null;
+
+            var result = GetPreviousSibling(e);
+
+            if (result != null)
+            {
+                if (IsGroup(result))
+                    return result;
+                else
+                    return GetLastInTree(result);
             }
             else
+                return GetParent(e);
+        }
+
+        private static IInputElement? GetPreviousSibling(IInputElement e)
+        {
+            if (GetParent(e) is IVisual parentAsVisual && e is IVisual elementAsVisual)
             {
-                next = direction == NavigationDirection.Next ?
-                    GetFocusableDescendants(container, direction).FirstOrDefault() :
-                    GetFocusableDescendants(container, direction).LastOrDefault();
+                var children = parentAsVisual.VisualChildren;
+                var count = children.Count;
+                IInputElement? prev = null;
+                
+                for (int i = 0; i < count; i++)
+                {
+                    var vchild = children[i];
+                    if (vchild == elementAsVisual)
+                        break;
+                    if (vchild.IsVisible == true && vchild is IInputElement ie)
+                        prev = ie;
+                }
+                return prev;
             }
+            return null;
+        }
 
-            return next;
+        private static IInputElement? GetActiveElement(IInputElement e)
+        {
+            return ((IAvaloniaObject)e).GetValue(KeyboardNavigation.TabOnceActiveElementProperty);
         }
 
-        private static (bool handled, IInputElement? next) GetCustomNext(IInputElement element,
-            NavigationDirection direction)
+        private static IInputElement GetGroupParent(IInputElement e) => GetGroupParent(e, false);
+
+        private static IInputElement GetGroupParent(IInputElement element, bool includeCurrent)
         {
-            if (element is ICustomKeyboardNavigation custom)
+            var result = element; // Keep the last non null element
+            var e = element;
+
+            // If we don't want to include the current element,
+            // start at the parent of the element.  If the element
+            // is the root, then just return it as the group parent.
+            if (!includeCurrent)
+            {
+                result = e;
+                e = GetParent(e);
+                if (e == null)
+                    return result;
+            }
+
+            while (e != null)
             {
-                return custom.GetNext(element, direction);
+                if (IsGroup(e))
+                    return e;
+
+                result = e;
+                e = GetParent(e);
             }
 
-            return (false, null);
+            return result;
         }
+
+        private static IInputElement? GetParent(IInputElement e)
+        {
+            // For Visual - go up the visual parent chain until we find Visual.
+            if (e is IVisual v)
+                return v.FindAncestorOfType<IInputElement>();
+
+            // This will need to be implemented when we have non-visual input elements.
+            throw new NotSupportedException();
+        }
+
+        private static KeyboardNavigationMode GetKeyNavigationMode(IInputElement e)
+        {
+            return ((IAvaloniaObject)e).GetValue(KeyboardNavigation.TabNavigationProperty);
+        }
+        private static bool IsFocusScope(IInputElement e) => FocusManager.GetIsFocusScope(e) || GetParent(e) == null;
+        private static bool IsGroup(IInputElement e) => GetKeyNavigationMode(e) != KeyboardNavigationMode.Continue;
+
+        private static bool IsTabStop(IInputElement e)
+        {
+            if (e is InputElement ie)
+                return ie.Focusable && KeyboardNavigation.GetIsTabStop(ie) && ie.IsVisible && ie.IsEnabled;
+            return false;
+        }
+
+        private static bool IsTabStopOrGroup(IInputElement e) => IsTabStop(e) || IsGroup(e);
     }
 }

src/Avalonia.Input/TappedEventArgs.cs

@@ -13,6 +13,10 @@ namespace Avalonia.Input
             this.lastPointerEventArgs = lastPointerEventArgs;
         }
 
+        public IPointer Pointer => lastPointerEventArgs.Pointer;
+        public KeyModifiers KeyModifiers => lastPointerEventArgs.KeyModifiers;
+        public ulong Timestamp => lastPointerEventArgs.Timestamp;
+        
         public Point GetPosition(IVisual? relativeTo) => lastPointerEventArgs.GetPosition(relativeTo);
     }
 }

src/Avalonia.Input/TextInput/ITextInputMethodClient.cs

@@ -22,11 +22,11 @@ namespace Avalonia.Input.TextInput
         /// </summary>
         event EventHandler TextViewVisualChanged;
         /// <summary>
-        /// Indicates if TextViewVisual is capable of displaying non-commited input on the cursor position
+        /// Indicates if TextViewVisual is capable of displaying non-committed input on the cursor position
         /// </summary>
         bool SupportsPreedit { get; }
         /// <summary>
-        /// Sets the non-commited input string
+        /// Sets the non-committed input string
         /// </summary>
         void SetPreeditText(string text);
         /// <summary>

src/Avalonia.Interactivity/Interactive.cs

@@ -143,7 +143,7 @@ namespace Avalonia.Interactivity
         /// <param name="e">The routed event.</param>
         /// <returns>An <see cref="EventRoute"/> describing the route.</returns>
         /// <remarks>
-        /// Usually, calling <see cref="RaiseEvent(RoutedEventArgs)"/> is sufficent to raise a routed
+        /// Usually, calling <see cref="RaiseEvent(RoutedEventArgs)"/> is sufficient to raise a routed
         /// event, however there are situations in which the construction of the event args is expensive
         /// and should be avoided if there are no handlers for an event. In these cases you can call
         /// this method to build the event route and check the <see cref="EventRoute.HasHandlers"/>