Merge branch 'master' into fixes/LineBreakEnumerator

6 years ago · 065538001e
39 changed files with 460 additions and 219 deletions
--- a/.github/ISSUE_TEMPLATE/bug_report.md
+++ b/.github/ISSUE_TEMPLATE/bug_report.md
@ -4,7 +4,6 @@ about: Create a report to help us improve Avalonia
 title: ''
 labels: bug
 assignees: ''
-
 ---

 **Describe the bug**
@ -12,6 +11,7 @@ A clear and concise description of what the bug is.

 **To Reproduce**
 Steps to reproduce the behavior:
+
 1. Go to '...'
 2. Click on '....'
 3. Scroll down to '....'
@ -24,8 +24,9 @@ A clear and concise description of what you expected to happen.
 If applicable, add screenshots to help explain your problem.

 **Desktop (please complete the following information):**
- - OS: [e.g. Windows, Mac, Linux (State distribution)]
- - Version [e.g. 0.10.0-rc1 or 0.9.12]
+
+- OS: [e.g. Windows, Mac, Linux (State distribution)]
+- Version [e.g. 0.10.0-rc1 or 0.9.12]

 **Additional context**
 Add any other context about the problem here.
--- a/.github/ISSUE_TEMPLATE/config.yml
+++ b/.github/ISSUE_TEMPLATE/config.yml
@ -0,0 +1,8 @@
+blank_issues_enabled: false
+contact_links:
+  - name: Questions, Discussions, Ideas
+    url: https://github.com/AvaloniaUI/Avalonia/discussions/new
+    about: Please ask and answer questions here.
+  - name: Avalonia Community Support on Gitter
+    url: https://gitter.im/AvaloniaUI/Avalonia
+    about: Please ask and answer questions here.
--- a/.github/ISSUE_TEMPLATE/feature_request.md
+++ b/.github/ISSUE_TEMPLATE/feature_request.md
@ -4,7 +4,6 @@ about: Suggest an idea for this project
 title: ''
 labels: enhancement
 assignees: ''
-
 ---

 **Is your feature request related to a problem? Please describe.**
--- a/native/Avalonia.Native/src/OSX/Screens.mm
+++ b/native/Avalonia.Native/src/OSX/Screens.mm
@ -5,12 +5,6 @@ class Screens : public ComSingleObject<IAvnScreens, &IID_IAvnScreens>
    public:
    FORWARD_IUNKNOWN()
    
-    private:
-    CGFloat PrimaryDisplayHeight()
-    {
-      return NSMaxY([[[NSScreen screens] firstObject] frame]);
-    }
-    
 public:
    virtual HRESULT GetScreenCount (int* ret) override
    {
@ -36,12 +30,12 @@ public:
            ret->Bounds.Height = [screen frame].size.height;
            ret->Bounds.Width = [screen frame].size.width;
            ret->Bounds.X = [screen frame].origin.x;
-            ret->Bounds.Y = PrimaryDisplayHeight() - [screen frame].origin.y - ret->Bounds.Height;
+            ret->Bounds.Y = ConvertPointY(ToAvnPoint([screen frame].origin)).Y - ret->Bounds.Height;
            
            ret->WorkingArea.Height = [screen visibleFrame].size.height;
            ret->WorkingArea.Width = [screen visibleFrame].size.width;
            ret->WorkingArea.X = [screen visibleFrame].origin.x;
-            ret->WorkingArea.Y = ret->Bounds.Height - [screen visibleFrame].origin.y - ret->WorkingArea.Height;
+            ret->WorkingArea.Y = ConvertPointY(ToAvnPoint([screen visibleFrame].origin)).Y - ret->WorkingArea.Height;
            
            ret->PixelDensity = [screen backingScaleFactor];
            
--- a/native/Avalonia.Native/src/OSX/common.h
+++ b/native/Avalonia.Native/src/OSX/common.h
@ -34,6 +34,7 @@ extern NSApplicationActivationPolicy AvnDesiredActivationPolicy;
 extern NSPoint ToNSPoint (AvnPoint p);
 extern AvnPoint ToAvnPoint (NSPoint p);
 extern AvnPoint ConvertPointY (AvnPoint p);
+extern CGFloat PrimaryDisplayHeight();
 extern NSSize ToNSSize (AvnSize s);
 #ifdef DEBUG
 #define NSDebugLog(...) NSLog(__VA_ARGS__)
--- a/native/Avalonia.Native/src/OSX/main.mm
+++ b/native/Avalonia.Native/src/OSX/main.mm
@ -299,10 +299,14 @@ AvnPoint ToAvnPoint (NSPoint p)

 AvnPoint ConvertPointY (AvnPoint p)
 {
-    auto sw = [NSScreen.screens objectAtIndex:0].frame;
+    auto primaryDisplayHeight = NSMaxY([[[NSScreen screens] firstObject] frame]);
    
-    auto t = MAX(sw.origin.y, sw.origin.y + sw.size.height);
-    p.Y = t - p.Y;
+    p.Y = primaryDisplayHeight - p.Y;
    
    return p;
 }
+
+CGFloat PrimaryDisplayHeight()
+{
+  return NSMaxY([[[NSScreen screens] firstObject] frame]);
+}
--- a/native/Avalonia.Native/src/OSX/window.mm
+++ b/native/Avalonia.Native/src/OSX/window.mm
@ -1391,17 +1391,20 @@ NSArray* AllLoopModes = [NSArray arrayWithObjects: NSDefaultRunLoopMode, NSEvent
    [super viewDidChangeBackingProperties];
 }

- (bool) ignoreUserInput
+- (bool) ignoreUserInput:(bool)trigerInputWhenDisabled
 {
    auto parentWindow = objc_cast<AvnWindow>([self window]);
    
    if(parentWindow == nil || ![parentWindow shouldTryToHandleEvents])
    {
-        auto window = dynamic_cast<WindowImpl*>(_parent.getRaw());
-        
-        if(window != nullptr)
+        if(trigerInputWhenDisabled)
        {
-            window->WindowEvents->GotInputWhenDisabled();
+            auto window = dynamic_cast<WindowImpl*>(_parent.getRaw());
+            
+            if(window != nullptr)
+            {
+                window->WindowEvents->GotInputWhenDisabled();
+            }
        }
        
        return TRUE;
@ -1412,7 +1415,9 @@ NSArray* AllLoopModes = [NSArray arrayWithObjects: NSDefaultRunLoopMode, NSEvent

 - (void)mouseEvent:(NSEvent *)event withType:(AvnRawMouseEventType) type
 {
-    if([self ignoreUserInput])
+    bool triggerInputWhenDisabled = type != Move;
+    
+    if([self ignoreUserInput: triggerInputWhenDisabled])
    {
        return;
    }
@ -1578,7 +1583,7 @@ NSArray* AllLoopModes = [NSArray arrayWithObjects: NSDefaultRunLoopMode, NSEvent

 - (void) keyboardEvent: (NSEvent *) event withType: (AvnRawKeyEventType)type
 {
-    if([self ignoreUserInput])
+    if([self ignoreUserInput: false])
    {
        return;
    }
--- a/samples/ControlCatalog/Pages/ScreenPage.cs
+++ b/samples/ControlCatalog/Pages/ScreenPage.cs
@ -29,7 +29,7 @@ namespace ControlCatalog.Pages
            var screens = w.Screens.All;
            var scaling = ((IRenderRoot)w).RenderScaling;

-            var drawBrush = Brushes.Green;
+            var drawBrush = Brushes.Black;
            Pen p = new Pen(drawBrush);
            if (screens != null)
                foreach (Screen screen in screens)
@ -45,18 +45,16 @@ namespace ControlCatalog.Pages
                                      screen.Bounds.Height / 10f);
                    Rect workingAreaRect = new Rect(screen.WorkingArea.X / 10f + Math.Abs(_leftMost), screen.WorkingArea.Y / 10f, screen.WorkingArea.Width / 10f,
                                       screen.WorkingArea.Height / 10f);
+                    
                    context.DrawRectangle(p, boundsRect);
                    context.DrawRectangle(p, workingAreaRect);
-                    
-                    FormattedText text = new FormattedText()
-                    {
-                        Typeface = Typeface.Default
-                    };

-                    text.Text = $"Bounds: {screen.Bounds.Width}:{screen.Bounds.Height}";
+                    var text = new FormattedText() { Typeface = new Typeface("Arial"), FontSize = 18 };
+
+                    text.Text = $"Bounds: {screen.Bounds.TopLeft} {screen.Bounds.Width}:{screen.Bounds.Height}";
                    context.DrawText(drawBrush, boundsRect.Position.WithY(boundsRect.Size.Height), text);
                    
-                    text.Text = $"WorkArea: {screen.WorkingArea.Width}:{screen.WorkingArea.Height}";
+                    text.Text = $"WorkArea: {screen.WorkingArea.TopLeft} {screen.WorkingArea.Width}:{screen.WorkingArea.Height}";
                    context.DrawText(drawBrush, boundsRect.Position.WithY(boundsRect.Size.Height + 20), text);

                    text.Text = $"Scaling: {screen.PixelDensity * 100}%";
@ -69,7 +67,7 @@ namespace ControlCatalog.Pages
                    context.DrawText(drawBrush, boundsRect.Position.WithY(boundsRect.Size.Height + 80), text);
                }

-            context.DrawRectangle(p, new Rect(w.Position.X / 10f + Math.Abs(_leftMost), w.Position.Y / 10, w.Bounds.Width / 10, w.Bounds.Height / 10));
+            context.DrawRectangle(p, new Rect(w.Position.X / 10f + Math.Abs(_leftMost), w.Position.Y / 10f, w.Bounds.Width / 10, w.Bounds.Height / 10));
        }
    }
 }
--- a/src/Avalonia.Controls/Button.cs
+++ b/src/Avalonia.Controls/Button.cs
@ -80,6 +80,7 @@ namespace Avalonia.Controls

        private ICommand _command;
        private bool _commandCanExecute = true;
+        private KeyGesture _hotkey;

        /// <summary>
        /// Initializes static members of the <see cref="Button"/> class.
@ -207,6 +208,11 @@ namespace Avalonia.Controls

        protected override void OnAttachedToLogicalTree(LogicalTreeAttachmentEventArgs e)
        {
+            if (_hotkey != null) // Control attached again, set Hotkey to create a hotkey manager for this control
+            {
+                HotKey = _hotkey;
+            }
+            
            base.OnAttachedToLogicalTree(e);

            if (Command != null)
@ -217,6 +223,13 @@ namespace Avalonia.Controls

        protected override void OnDetachedFromLogicalTree(LogicalTreeAttachmentEventArgs e)
        {
+            // This will cause the hotkey manager to dispose the observer and the reference to this control
+            if (HotKey != null)
+            {
+                _hotkey = HotKey;
+                HotKey = null;
+            }
+
            base.OnDetachedFromLogicalTree(e);

            if (Command != null)
--- a/src/Avalonia.Controls/MenuItem.cs
+++ b/src/Avalonia.Controls/MenuItem.cs
@ -102,6 +102,7 @@ namespace Avalonia.Controls
        private ICommand? _command;
        private bool _commandCanExecute = true;
        private Popup? _popup;
+        private KeyGesture _hotkey;

        /// <summary>
        /// Initializes static members of the <see cref="MenuItem"/> class.
@ -111,6 +112,7 @@ namespace Avalonia.Controls
            SelectableMixin.Attach<MenuItem>(IsSelectedProperty);
            PressedMixin.Attach<MenuItem>();
            CommandProperty.Changed.Subscribe(CommandChanged);
+            CommandParameterProperty.Changed.Subscribe(CommandParameterChanged);
            FocusableProperty.OverrideDefaultValue<MenuItem>(true);
            HeaderProperty.Changed.AddClassHandler<MenuItem>((x, e) => x.HeaderChanged(e));
            IconProperty.Changed.AddClassHandler<MenuItem>((x, e) => x.IconChanged(e));
@ -337,6 +339,11 @@ namespace Avalonia.Controls

        protected override void OnAttachedToLogicalTree(LogicalTreeAttachmentEventArgs e)
        {
+            if (_hotkey != null) // Control attached again, set Hotkey to create a hotkey manager for this control
+            {
+                HotKey = _hotkey;
+            }
+            
            base.OnAttachedToLogicalTree(e);

            if (Command != null)
@ -347,6 +354,13 @@ namespace Avalonia.Controls

        protected override void OnDetachedFromLogicalTree(LogicalTreeAttachmentEventArgs e)
        {
+            // This will cause the hotkey manager to dispose the observer and the reference to this control
+            if (HotKey != null)
+            {
+                _hotkey = HotKey;
+                HotKey = null;
+            }
+
            base.OnDetachedFromLogicalTree(e);

            if (Command != null)
@ -493,6 +507,18 @@ namespace Avalonia.Controls
            }
        }

+        /// <summary>
+        /// Called when the <see cref="CommandParameter"/> property changes.
+        /// </summary>
+        /// <param name="e">The event args.</param>
+        private static void CommandParameterChanged(AvaloniaPropertyChangedEventArgs e)
+        {
+            if (e.Sender is MenuItem menuItem)
+            {
+                menuItem.CanExecuteChanged(menuItem, EventArgs.Empty);
+            }
+        }
+
        /// <summary>
        /// Called when the <see cref="ICommand.CanExecuteChanged"/> event fires.
        /// </summary>
--- a/src/Avalonia.Controls/Utils/AncestorFinder.cs
+++ b/src/Avalonia.Controls/Utils/AncestorFinder.cs
@ -47,6 +47,8 @@ namespace Avalonia.Controls.Utils

            public void Dispose()
            {
+                _child?.Dispose();
+                _subject.Dispose();
                _disposable.Dispose();
            }
        }
--- a/src/Avalonia.Native/WindowImplBase.cs
+++ b/src/Avalonia.Native/WindowImplBase.cs
@ -383,7 +383,7 @@ namespace Avalonia.Native
            _native.BeginMoveDrag();
        }

-        public Size MaxAutoSizeHint => Screen.AllScreens.Select(s => s.Bounds.Size.ToSize(s.PixelDensity))
+        public Size MaxAutoSizeHint => Screen.AllScreens.Select(s => s.Bounds.Size.ToSize(1))
            .OrderByDescending(x => x.Width + x.Height).FirstOrDefault();

        public void SetTopmost(bool value)
--- a/src/Markup/Avalonia.Markup.Xaml.Loader/CompilerExtensions/Transformers/IgnoredDirectivesTransformer.cs
+++ b/src/Markup/Avalonia.Markup.Xaml.Loader/CompilerExtensions/Transformers/IgnoredDirectivesTransformer.cs
@ -15,7 +15,10 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers
                {
                    if (d.Namespace == XamlNamespaces.Xaml2006)
                    {
-                        if (d.Name == "Precompile" || d.Name == "Class")
+                        if (d.Name == "Precompile" ||
+                            d.Name == "Class" ||
+                            d.Name == "FieldModifier" ||
+                            d.Name == "ClassModifier")
                            no.Children.Remove(d);
                    }
                }
--- a/src/Markup/Avalonia.Markup/Avalonia.Markup.csproj
+++ b/src/Markup/Avalonia.Markup/Avalonia.Markup.csproj
@ -2,6 +2,8 @@
  <PropertyGroup>
    <TargetFramework>netstandard2.0</TargetFramework>
    <RootNamespace>Avalonia</RootNamespace>
+    <Nullable>Enable</Nullable>
+    <WarningsAsErrors>CS8600;CS8602;CS8603</WarningsAsErrors>
  </PropertyGroup>
  <ItemGroup>
    <None Remove="Markup\Parsers\Nodes\ExpressionGrammer" />
--- a/src/Markup/Avalonia.Markup/Data/Binding.cs
+++ b/src/Markup/Avalonia.Markup/Data/Binding.cs
@ -39,17 +39,17 @@ namespace Avalonia.Data
        /// <summary>
        /// Gets or sets the name of the element to use as the binding source.
        /// </summary>
-        public string ElementName { get; set; }
+        public string? ElementName { get; set; }

        /// <summary>
        /// Gets or sets the relative source for the binding.
        /// </summary>
-        public RelativeSource RelativeSource { get; set; }
+        public RelativeSource? RelativeSource { get; set; }

        /// <summary>
        /// Gets or sets the source for the binding.
        /// </summary>
-        public object Source { get; set; }
+        public object? Source { get; set; }

        /// <summary>
        /// Gets or sets the binding path.
@ -59,24 +59,36 @@ namespace Avalonia.Data
        /// <summary>
        /// Gets or sets a function used to resolve types from names in the binding path.
        /// </summary>
-        public Func<string, string, Type> TypeResolver { get; set; }
+        public Func<string, string, Type>? TypeResolver { get; set; }

-        protected override ExpressionObserver CreateExpressionObserver(IAvaloniaObject target, AvaloniaProperty targetProperty, object anchor, bool enableDataValidation)
+        protected override ExpressionObserver CreateExpressionObserver(IAvaloniaObject target, AvaloniaProperty targetProperty, object? anchor, bool enableDataValidation)
        {
-            Contract.Requires<ArgumentNullException>(target != null);
-            anchor = anchor ?? DefaultAnchor?.Target;
-            
+            _ = target ?? throw new ArgumentNullException(nameof(target));
+
+            anchor ??= DefaultAnchor?.Target;
            enableDataValidation = enableDataValidation && Priority == BindingPriority.LocalValue;

-            INameScope nameScope = null;
+            INameScope? nameScope = null;
            NameScope?.TryGetTarget(out nameScope);

            var (node, mode) = ExpressionObserverBuilder.Parse(Path, enableDataValidation, TypeResolver, nameScope);

+            if (node is null)
+            {
+                throw new InvalidOperationException("Could not parse binding expression.");
+            }
+
+            IStyledElement GetSource()
+            {
+                return target as IStyledElement ??
+                    anchor as IStyledElement ??
+                    throw new ArgumentException("Could not find binding source: either target or anchor must be an IStyledElement.");
+            }
+
            if (ElementName != null)
            {
                return CreateElementObserver(
-                    (target as IStyledElement) ?? (anchor as IStyledElement),
+                    GetSource(),
                    ElementName,
                    node);
            }
@ -96,9 +108,7 @@ namespace Avalonia.Data
                }
                else
                {
-                    return CreateSourceObserver(
-                        (target as IStyledElement) ?? (anchor as IStyledElement),
-                        node);
+                    return CreateSourceObserver(GetSource(), node);
                }
            }
            else if (RelativeSource.Mode == RelativeSourceMode.DataContext)
@ -111,15 +121,11 @@ namespace Avalonia.Data
            }
            else if (RelativeSource.Mode == RelativeSourceMode.Self)
            {
-                return CreateSourceObserver(
-                    (target as IStyledElement) ?? (anchor as IStyledElement),
-                    node);
+                return CreateSourceObserver(GetSource(), node);
            }
            else if (RelativeSource.Mode == RelativeSourceMode.TemplatedParent)
            {
-                return CreateTemplatedParentObserver(
-                    (target as IStyledElement) ?? (anchor as IStyledElement),
-                    node);
+                return CreateTemplatedParentObserver(GetSource(), node);
            }
            else if (RelativeSource.Mode == RelativeSourceMode.FindAncestor)
            {
@ -128,10 +134,7 @@ namespace Avalonia.Data
                    throw new InvalidOperationException("AncestorType must be set for RelativeSourceMode.FindAncestor when searching the visual tree.");
                }

-                return CreateFindAncestorObserver(
-                    (target as IStyledElement) ?? (anchor as IStyledElement),
-                    RelativeSource,
-                    node);
+                return CreateFindAncestorObserver(GetSource(), RelativeSource, node);
            }
            else
            {
--- a/src/Markup/Avalonia.Markup/Data/BindingBase.cs
+++ b/src/Markup/Avalonia.Markup/Data/BindingBase.cs
@ -38,22 +38,22 @@ namespace Avalonia.Data
        /// <summary>
        /// Gets or sets the <see cref="IValueConverter"/> to use.
        /// </summary>
-        public IValueConverter Converter { get; set; }
+        public IValueConverter? Converter { get; set; }

        /// <summary>
        /// Gets or sets a parameter to pass to <see cref="Converter"/>.
        /// </summary>
-        public object ConverterParameter { get; set; }
+        public object? ConverterParameter { get; set; }

        /// <summary>
        /// Gets or sets the value to use when the binding is unable to produce a value.
        /// </summary>
-        public object FallbackValue { get; set; }
+        public object? FallbackValue { get; set; }

        /// <summary>
        /// Gets or sets the value to use when the binding result is null.
        /// </summary>
-        public object TargetNullValue { get; set; }
+        public object? TargetNullValue { get; set; }

        /// <summary>
        /// Gets or sets the binding mode.
@ -68,26 +68,27 @@ namespace Avalonia.Data
        /// <summary>
        /// Gets or sets the string format.
        /// </summary>
-        public string StringFormat { get; set; }
+        public string? StringFormat { get; set; }

-        public WeakReference DefaultAnchor { get; set; }
+        public WeakReference? DefaultAnchor { get; set; }

-        public WeakReference<INameScope> NameScope { get; set; }
+        public WeakReference<INameScope>? NameScope { get; set; }

        protected abstract ExpressionObserver CreateExpressionObserver(
            IAvaloniaObject target,
            AvaloniaProperty targetProperty,
-            object anchor,
+            object? anchor,
            bool enableDataValidation);

        /// <inheritdoc/>
        public InstancedBinding Initiate(
            IAvaloniaObject target,
            AvaloniaProperty targetProperty,
-            object anchor = null,
+            object? anchor = null,
            bool enableDataValidation = false)
        {
-            Contract.Requires<ArgumentNullException>(target != null);
+            _ = target ?? throw new ArgumentNullException(nameof(target));
+
            anchor = anchor ?? DefaultAnchor?.Target;

            enableDataValidation = enableDataValidation && Priority == BindingPriority.LocalValue;
@ -133,18 +134,13 @@ namespace Avalonia.Data
            IAvaloniaObject target,
            ExpressionNode node,
            bool targetIsDataContext,
-            object anchor)
+            object? anchor)
        {
-            Contract.Requires<ArgumentNullException>(target != null);
+            _ = target ?? throw new ArgumentNullException(nameof(target));

            if (!(target is IDataContextProvider))
            {
-                target = anchor as IDataContextProvider;
-
-                if (target == null)
-                {
-                    throw new InvalidOperationException("Cannot find a DataContext to bind to.");
-                }
+                target = anchor as IDataContextProvider ?? throw new InvalidOperationException("Cannot find a DataContext to bind to.");
            }

            if (!targetIsDataContext)
@ -171,10 +167,9 @@ namespace Avalonia.Data
            string elementName,
            ExpressionNode node)
        {
-            Contract.Requires<ArgumentNullException>(target != null);
+            _ = target ?? throw new ArgumentNullException(nameof(target));

-            NameScope.TryGetTarget(out var scope);
-            if (scope == null)
+            if (NameScope is null || !NameScope.TryGetTarget(out var scope) || scope is null)
                throw new InvalidOperationException("Name scope is null or was already collected");
            var result = new ExpressionObserver(
                NameScopeLocator.Track(scope, elementName),
@ -188,9 +183,9 @@ namespace Avalonia.Data
            RelativeSource relativeSource,
            ExpressionNode node)
        {
-            Contract.Requires<ArgumentNullException>(target != null);
+            _ = target ?? throw new ArgumentNullException(nameof(target));

-            IObservable<object> controlLocator;
+            IObservable<object?> controlLocator;

            switch (relativeSource.Tree)
            {
@ -220,7 +215,7 @@ namespace Avalonia.Data
            object source,
            ExpressionNode node)
        {
-            Contract.Requires<ArgumentNullException>(source != null);
+            _ = source ?? throw new ArgumentNullException(nameof(source));

            return new ExpressionObserver(source, node);
        }
@ -229,7 +224,7 @@ namespace Avalonia.Data
            IAvaloniaObject target,
            ExpressionNode node)
        {
-            Contract.Requires<ArgumentNullException>(target != null);
+            _ = target ?? throw new ArgumentNullException(nameof(target));

            var result = new ExpressionObserver(
                () => target.GetValue(StyledElement.TemplatedParentProperty),
@ -240,7 +235,7 @@ namespace Avalonia.Data
            return result;
        }

-        protected IObservable<object> GetParentDataContext(IAvaloniaObject target)
+        protected IObservable<object?> GetParentDataContext(IAvaloniaObject target)
        {
            // The DataContext is based on the visual parent and not the logical parent: this may
            // seem counter intuitive considering the fact that property inheritance works on the logical
@ -252,7 +247,7 @@ namespace Avalonia.Data
                .Select(x =>
                {
                    return (x as IAvaloniaObject)?.GetObservable(StyledElement.DataContextProperty) ??
-                           Observable.Return((object)null);
+                           Observable.Return((object?)null);
                }).Switch();
        }

--- a/src/Markup/Avalonia.Markup/Data/MultiBinding.cs
+++ b/src/Markup/Avalonia.Markup/Data/MultiBinding.cs
@ -22,12 +22,12 @@ namespace Avalonia.Data
        /// <summary>
        /// Gets or sets the <see cref="IMultiValueConverter"/> to use.
        /// </summary>
-        public IMultiValueConverter Converter { get; set; }
+        public IMultiValueConverter? Converter { get; set; }

        /// <summary>
        /// Gets or sets a parameter to pass to <see cref="Converter"/>.
        /// </summary>
-        public object ConverterParameter { get; set; }
+        public object? ConverterParameter { get; set; }

        /// <summary>
        /// Gets or sets the value to use when the binding is unable to produce a value.
@ -52,12 +52,12 @@ namespace Avalonia.Data
        /// <summary>
        /// Gets or sets the relative source for the binding.
        /// </summary>
-        public RelativeSource RelativeSource { get; set; }
+        public RelativeSource? RelativeSource { get; set; }

        /// <summary>
        /// Gets or sets the string format.
        /// </summary>
-        public string StringFormat { get; set; }
+        public string? StringFormat { get; set; }

        public MultiBinding()
        {
@ -69,7 +69,7 @@ namespace Avalonia.Data
        public InstancedBinding Initiate(
            IAvaloniaObject target,
            AvaloniaProperty targetProperty,
-            object anchor = null,
+            object? anchor = null,
            bool enableDataValidation = false)
        {
            var targetType = targetProperty?.PropertyType ?? typeof(object);
@ -105,7 +105,7 @@ namespace Avalonia.Data
            }
        }

-        private object ConvertValue(IList<object> values, Type targetType, IMultiValueConverter converter)
+        private object ConvertValue(IList<object?> values, Type targetType, IMultiValueConverter? converter)
        {
            for (var i = 0; i < values.Count; ++i)
            {
@ -116,7 +116,7 @@ namespace Avalonia.Data
            }

            var culture = CultureInfo.CurrentCulture;
-            values = new System.Collections.ObjectModel.ReadOnlyCollection<object>(values);
+            values = new System.Collections.ObjectModel.ReadOnlyCollection<object?>(values);
            object converted;
            if (converter != null)
            {
--- a/src/Markup/Avalonia.Markup/Data/RelativeSource.cs
+++ b/src/Markup/Avalonia.Markup/Data/RelativeSource.cs
@ -94,7 +94,7 @@ namespace Avalonia.Data
        /// <summary>
        /// Gets the type of ancestor to look for when in <see cref="RelativeSourceMode.FindAncestor"/>  mode.
        /// </summary>
-        public Type AncestorType { get; set; }
+        public Type? AncestorType { get; set; }

        /// <summary>
        /// Gets or sets a value that describes the type of relative source lookup.
--- a/src/Markup/Avalonia.Markup/Data/TemplateBinding.cs
+++ b/src/Markup/Avalonia.Markup/Data/TemplateBinding.cs
@ -17,8 +17,8 @@ namespace Avalonia.Data
        ISetterValue
    {
        private bool _isSetterValue;
-        private IStyledElement _target;
-        private Type _targetType;
+        private IStyledElement _target = default!;
+        private Type? _targetType;

        public TemplateBinding()
        {
@ -33,7 +33,7 @@ namespace Avalonia.Data
        public InstancedBinding Initiate(
            IAvaloniaObject target,
            AvaloniaProperty targetProperty,
-            object anchor = null,
+            object? anchor = null,
            bool enableDataValidation = false)
        {
            // Usually each `TemplateBinding` will only be instantiated once; in this case we can
@ -68,12 +68,12 @@ namespace Avalonia.Data
        /// <summary>
        /// Gets or sets the <see cref="IValueConverter"/> to use.
        /// </summary>
-        public IValueConverter Converter { get; set; }
+        public IValueConverter? Converter { get; set; }

        /// <summary>
        /// Gets or sets a parameter to pass to <see cref="Converter"/>.
        /// </summary>
-        public object ConverterParameter { get; set; }
+        public object? ConverterParameter { get; set; }

        /// <summary>
        /// Gets or sets the binding mode.
@ -83,7 +83,7 @@ namespace Avalonia.Data
        /// <summary>
        /// Gets or sets the name of the source property on the templated parent.
        /// </summary>
-        public AvaloniaProperty Property { get; set; }
+        public AvaloniaProperty? Property { get; set; }

        /// <inheritdoc/>
        public string Description => "TemplateBinding: " + Property;
@ -164,10 +164,7 @@ namespace Avalonia.Data
        {
            if (e.Property == StyledElement.TemplatedParentProperty)
            {
-                var oldValue = (IAvaloniaObject)e.OldValue;
-                var newValue = (IAvaloniaObject)e.OldValue;
-
-                if (oldValue != null)
+                if (e.OldValue is IAvaloniaObject oldValue)
                {
                    oldValue.PropertyChanged -= TemplatedParentPropertyChanged;
                }
--- a/src/Markup/Avalonia.Markup/Markup/Parsers/BindingExpressionGrammar.cs
+++ b/src/Markup/Avalonia.Markup/Markup/Parsers/BindingExpressionGrammar.cs
@ -6,6 +6,8 @@ using Avalonia.Utilities;
 using System;
 using System.Collections.Generic;

+#nullable enable
+
 namespace Avalonia.Markup.Parsers
 {
    internal enum SourceMode
@ -271,8 +273,8 @@ namespace Avalonia.Markup.Parsers
            }
            else if (mode.SequenceEqual("parent".AsSpan()))
            {
-                string ancestorNamespace = null;
-                string ancestorType = null;
+                string? ancestorNamespace = null;
+                string? ancestorType = null;
                var ancestorLevel = 0;
                if (PeekOpenBracket(ref r))
                {
@ -424,19 +426,19 @@ namespace Avalonia.Markup.Parsers

        public class PropertyNameNode : INode
        {
-            public string PropertyName { get; set; }
+            public string PropertyName { get; set; } = string.Empty;
        }

        public class AttachedPropertyNameNode : INode
        {
-            public string Namespace { get; set; }
-            public string TypeName { get; set; }
-            public string PropertyName { get; set; }
+            public string Namespace { get; set; } = string.Empty;
+            public string TypeName { get; set; } = string.Empty;
+            public string PropertyName { get; set; } = string.Empty;
        }

        public class IndexerNode : INode
        {
-            public IList<string> Arguments { get; set; }
+            public IList<string> Arguments { get; set; } = Array.Empty<string>();
        }

        public class NotNode : INode, ITransformNode { }
@ -447,20 +449,20 @@ namespace Avalonia.Markup.Parsers

        public class NameNode : INode
        {
-            public string Name { get; set; }
+            public string Name { get; set; } = string.Empty;
        }

        public class AncestorNode : INode
        {
-            public string Namespace { get; set; }
-            public string TypeName { get; set; }
+            public string? Namespace { get; set; }
+            public string? TypeName { get; set; }
            public int Level { get; set; }
        }

        public class TypeCastNode : INode
        {
-            public string Namespace { get; set; }
-            public string TypeName { get; set; }
+            public string Namespace { get; set; } = string.Empty;
+            public string TypeName { get; set; } = string.Empty;
        }
    }
 }
--- a/src/Markup/Avalonia.Markup/Markup/Parsers/ExpressionObserverBuilder.cs
+++ b/src/Markup/Avalonia.Markup/Markup/Parsers/ExpressionObserverBuilder.cs
@ -8,8 +8,8 @@ namespace Avalonia.Markup.Parsers
 {
    public static class ExpressionObserverBuilder
    {
-        internal static (ExpressionNode Node, SourceMode Mode) Parse(string expression, bool enableValidation = false, Func<string, string, Type> typeResolver = null,
-            INameScope nameScope = null)
+        internal static (ExpressionNode? Node, SourceMode Mode) Parse(string expression, bool enableValidation = false, Func<string, string, Type>? typeResolver = null,
+            INameScope? nameScope = null)
        {
            if (string.IsNullOrWhiteSpace(expression))
            {
@ -32,8 +32,8 @@ namespace Avalonia.Markup.Parsers
            object root,
            string expression,
            bool enableDataValidation = false,
-            string description = null,
-            Func<string, string, Type> typeResolver = null)
+            string? description = null,
+            Func<string, string, Type>? typeResolver = null)
        {
            return new ExpressionObserver(
                root,
@ -45,10 +45,11 @@ namespace Avalonia.Markup.Parsers
            IObservable<object> rootObservable,
            string expression,
            bool enableDataValidation = false,
-            string description = null,
-            Func<string, string, Type> typeResolver = null)
+            string? description = null,
+            Func<string, string, Type>? typeResolver = null)
        {
-            Contract.Requires<ArgumentNullException>(rootObservable != null);
+            _ = rootObservable ?? throw new ArgumentNullException(nameof(rootObservable));
+
            return new ExpressionObserver(
                rootObservable,
                Parse(expression, enableDataValidation, typeResolver).Node,
@ -61,10 +62,10 @@ namespace Avalonia.Markup.Parsers
            string expression,
            IObservable<Unit> update,
            bool enableDataValidation = false,
-            string description = null,
-            Func<string, string, Type> typeResolver = null)
+            string? description = null,
+            Func<string, string, Type>? typeResolver = null)
        {
-            Contract.Requires<ArgumentNullException>(rootGetter != null);
+            _ = rootGetter ?? throw new ArgumentNullException(nameof(rootGetter));

            return new ExpressionObserver(
                rootGetter,
--- a/src/Markup/Avalonia.Markup/Markup/Parsers/ExpressionParser.cs
+++ b/src/Markup/Avalonia.Markup/Markup/Parsers/ExpressionParser.cs
@ -11,25 +11,25 @@ namespace Avalonia.Markup.Parsers
    internal class ExpressionParser
    {
        private readonly bool _enableValidation;
-        private readonly Func<string, string, Type> _typeResolver;
-        private readonly INameScope _nameScope;
+        private readonly Func<string, string, Type>? _typeResolver;
+        private readonly INameScope? _nameScope;

-        public ExpressionParser(bool enableValidation, Func<string, string, Type> typeResolver, INameScope nameScope)
+        public ExpressionParser(bool enableValidation, Func<string, string, Type>? typeResolver, INameScope? nameScope)
        {
            _typeResolver = typeResolver;
            _nameScope = nameScope;
            _enableValidation = enableValidation;
        }

-        public (ExpressionNode Node, SourceMode Mode) Parse(ref CharacterReader r)
+        public (ExpressionNode? Node, SourceMode Mode) Parse(ref CharacterReader r)
        {
-            ExpressionNode rootNode = null;
-            ExpressionNode node = null;
+            ExpressionNode? rootNode = null;
+            ExpressionNode? node = null;
            var (astNodes, mode) = BindingExpressionGrammar.Parse(ref r);

            foreach (var astNode in astNodes)
            {
-                ExpressionNode nextNode = null;
+                ExpressionNode? nextNode = null;
                switch (astNode)
                {
                    case BindingExpressionGrammar.EmptyExpressionNode _:
@ -57,13 +57,13 @@ namespace Avalonia.Markup.Parsers
                        nextNode = ParseFindAncestor(ancestor);
                        break;
                    case BindingExpressionGrammar.NameNode elementName:
-                        nextNode = new ElementNameNode(_nameScope, elementName.Name);
+                        nextNode = new ElementNameNode(_nameScope ?? throw new NotSupportedException("Invalid element name binding with null name scope!"), elementName.Name);
                        break;
                    case BindingExpressionGrammar.TypeCastNode typeCast:
                        nextNode = ParseTypeCastNode(typeCast);
                        break;
                }
-                if (rootNode is null)
+                if (node is null)
                {
                    rootNode = node = nextNode;
                }
@ -79,7 +79,7 @@ namespace Avalonia.Markup.Parsers

        private FindAncestorNode ParseFindAncestor(BindingExpressionGrammar.AncestorNode node)
        {
-            Type ancestorType = null;
+            Type? ancestorType = null;
            var ancestorLevel = node.Level;

            if (!(node.Namespace is null) && !(node.TypeName is null))
@ -97,7 +97,7 @@ namespace Avalonia.Markup.Parsers

        private TypeCastNode ParseTypeCastNode(BindingExpressionGrammar.TypeCastNode node)
        {
-            Type castType = null;
+            Type? castType = null;
            if (!(node.Namespace is null) && !(node.TypeName is null))
            {
                if (_typeResolver == null)
--- a/src/Markup/Avalonia.Markup/Markup/Parsers/Nodes/ElementNameNode.cs
+++ b/src/Markup/Avalonia.Markup/Markup/Parsers/Nodes/ElementNameNode.cs
@ -9,7 +9,7 @@ namespace Avalonia.Markup.Parsers.Nodes
    {
        private readonly WeakReference<INameScope> _nameScope;
        private readonly string _name;
-        private IDisposable _subscription;
+        private IDisposable? _subscription;

        public ElementNameNode(INameScope nameScope, string name)
        {
--- a/src/Markup/Avalonia.Markup/Markup/Parsers/Nodes/FindAncestorNode.cs
+++ b/src/Markup/Avalonia.Markup/Markup/Parsers/Nodes/FindAncestorNode.cs
@ -7,10 +7,10 @@ namespace Avalonia.Markup.Parsers.Nodes
    public class FindAncestorNode : ExpressionNode
    {
        private readonly int _level;
-        private readonly Type _ancestorType;
-        private IDisposable _subscription;
+        private readonly Type? _ancestorType;
+        private IDisposable? _subscription;

-        public FindAncestorNode(Type ancestorType, int level)
+        public FindAncestorNode(Type? ancestorType, int level)
        {
            _level = level;
            _ancestorType = ancestorType;
--- a/src/Markup/Avalonia.Markup/Markup/Parsers/Nodes/StringIndexerNode.cs
+++ b/src/Markup/Avalonia.Markup/Markup/Parsers/Nodes/StringIndexerNode.cs
@ -29,15 +29,15 @@ namespace Avalonia.Markup.Parsers.Nodes
            var list = target as IList;
            var dictionary = target as IDictionary;
            var indexerProperty = GetIndexer(typeInfo);
-            var indexerParameters = indexerProperty?.GetIndexParameters();
+            ParameterInfo[] indexerParameters;

-            if (indexerProperty != null && indexerParameters.Length == Arguments.Count)
+            if (indexerProperty != null && (indexerParameters = indexerProperty.GetIndexParameters()).Length == Arguments.Count)
            {
                var convertedObjectArray = new object[indexerParameters.Length];

                for (int i = 0; i < Arguments.Count; i++)
                {
-                    object temp = null;
+                    object? temp = null;

                    if (!TypeUtilities.TryConvert(indexerParameters[i].ParameterType, Arguments[i], CultureInfo.InvariantCulture, out temp))
                    {
@ -125,7 +125,7 @@ namespace Avalonia.Markup.Parsers.Nodes

        public IList<string> Arguments { get; }

-        public override Type PropertyType
+        public override Type? PropertyType
        {
            get
            {
@ -144,15 +144,15 @@ namespace Avalonia.Markup.Parsers.Nodes
            var list = target as IList;
            var dictionary = target as IDictionary;
            var indexerProperty = GetIndexer(typeInfo);
-            var indexerParameters = indexerProperty?.GetIndexParameters();
+            ParameterInfo[] indexerParameters;

-            if (indexerProperty != null && indexerParameters.Length == Arguments.Count)
+            if (indexerProperty != null && (indexerParameters = indexerProperty.GetIndexParameters()).Length == Arguments.Count)
            {
                var convertedObjectArray = new object[indexerParameters.Length];

                for (int i = 0; i < Arguments.Count; i++)
                {
-                    object temp = null;
+                    object? temp = null;

                    if (!TypeUtilities.TryConvert(indexerParameters[i].ParameterType, Arguments[i], CultureInfo.InvariantCulture, out temp))
                    {
@ -246,7 +246,7 @@ namespace Avalonia.Markup.Parsers.Nodes
            return true;
        }

-        private static PropertyInfo GetIndexer(TypeInfo typeInfo)
+        private static PropertyInfo? GetIndexer(TypeInfo? typeInfo)
        {
            PropertyInfo indexer;

--- a/src/Markup/Avalonia.Markup/Markup/Parsers/PropertyPathGrammar.cs
+++ b/src/Markup/Avalonia.Markup/Markup/Parsers/PropertyPathGrammar.cs
@ -3,6 +3,8 @@ using System.Collections.Generic;
 using Avalonia.Data.Core;
 using Avalonia.Utilities;

+#nullable enable
+
 namespace Avalonia.Markup.Parsers
 {
 #if !BUILDTASK
@ -30,7 +32,7 @@ namespace Avalonia.Markup.Parsers
            var parsed = new List<ISyntax>();
            while (state != State.End)
            {
-                ISyntax syntax = null;
+                ISyntax? syntax = null;
                if (state == State.Start)
                    (state, syntax) = ParseStart(ref r);
                else if (state == State.Next)
@ -53,7 +55,7 @@ namespace Avalonia.Markup.Parsers
            return parsed;
        }
        
-        private static (State, ISyntax) ParseNext(ref CharacterReader r)
+        private static (State, ISyntax?) ParseNext(ref CharacterReader r)
        {
            r.SkipWhitespace();
            if (r.End)
@ -106,7 +108,7 @@ namespace Avalonia.Markup.Parsers
                });
        }

-        static (string ns, string name) ParseXamlIdentifier(ref CharacterReader r)
+        static (string? ns, string name) ParseXamlIdentifier(ref CharacterReader r)
        {
            var ident = r.ParseIdentifier();
            if (ident.IsEmpty)
@ -147,7 +149,7 @@ namespace Avalonia.Markup.Parsers
            return true;
        }
        
-        private static (State, ISyntax) ParseAfterProperty(ref CharacterReader r)
+        private static (State, ISyntax?) ParseAfterProperty(ref CharacterReader r)
        {
            if (TryParseCasts(ref r, out var rv))
                return rv;
@ -184,20 +186,20 @@ namespace Avalonia.Markup.Parsers

        public class PropertySyntax : ISyntax
        {
-            public string Name { get; set; }
+            public string Name { get; set; } = string.Empty;

-            public override bool Equals(object obj)
+            public override bool Equals(object? obj)
                => obj is PropertySyntax other
                   && other.Name == Name;
        }
        
        public class TypeQualifiedPropertySyntax : ISyntax
        {
-            public string Name { get; set; }
-            public string TypeName { get; set; }
-            public string TypeNamespace { get; set; }
+            public string Name { get; set; } = string.Empty;
+            public string TypeName { get; set; } = string.Empty;
+            public string? TypeNamespace { get; set; }

-            public override bool Equals(object obj)
+            public override bool Equals(object? obj)
                => obj is TypeQualifiedPropertySyntax other
                   && other.Name == Name
                   && other.TypeName == TypeName
@ -207,14 +209,14 @@ namespace Avalonia.Markup.Parsers
        public class ChildTraversalSyntax : ISyntax
        {
            public static ChildTraversalSyntax Instance { get;  } = new ChildTraversalSyntax();
-            public override bool Equals(object obj) => obj is ChildTraversalSyntax;
+            public override bool Equals(object? obj) => obj is ChildTraversalSyntax;
        }
        
        public class EnsureTypeSyntax : ISyntax
        {
-            public string TypeName { get; set; }
-            public string TypeNamespace { get; set; }
-            public override bool Equals(object obj)
+            public string TypeName { get; set; } = string.Empty;
+            public string? TypeNamespace { get; set; }
+            public override bool Equals(object? obj)
                => obj is EnsureTypeSyntax other
                   && other.TypeName == TypeName
                   && other.TypeNamespace == TypeNamespace;
@ -222,9 +224,9 @@ namespace Avalonia.Markup.Parsers
        
        public class CastTypeSyntax : ISyntax
        {
-            public string TypeName { get; set; }
-            public string TypeNamespace { get; set; }
-            public override bool Equals(object obj)
+            public string TypeName { get; set; } = string.Empty;
+            public string? TypeNamespace { get; set; }
+            public override bool Equals(object? obj)
                => obj is CastTypeSyntax other
                   && other.TypeName == TypeName
                   && other.TypeNamespace == TypeNamespace;
--- a/src/Markup/Avalonia.Markup/Markup/Parsers/SelectorGrammar.cs
+++ b/src/Markup/Avalonia.Markup/Markup/Parsers/SelectorGrammar.cs
@ -4,6 +4,8 @@ using System.Linq;
 using Avalonia.Data.Core;
 using Avalonia.Utilities;

+#nullable enable
+
 // Don't need to override GetHashCode as the ISyntax objects will not be stored in a hash; the 
 // only reason they have overridden Equals methods is for unit testing.
 #pragma warning disable 659
@ -39,7 +41,7 @@ namespace Avalonia.Markup.Parsers
            var selector = new List<ISyntax>();
            while (!r.End && state != State.End)
            {
-                ISyntax syntax = null;
+                ISyntax? syntax = null;
                switch (state)
                {
                    case State.Start:
@ -110,7 +112,7 @@ namespace Avalonia.Markup.Parsers
            return State.TypeName;
        }

-        private static (State, ISyntax) ParseMiddle(ref CharacterReader r, char? end)
+        private static (State, ISyntax?) ParseMiddle(ref CharacterReader r, char? end)
        {
            if (r.TakeIf(':'))
            {
@ -190,7 +192,7 @@ namespace Avalonia.Markup.Parsers
            }
        }

-        private static (State, ISyntax) ParseTraversal(ref CharacterReader r)
+        private static (State, ISyntax?) ParseTraversal(ref CharacterReader r)
        {
            r.SkipWhitespace();
            if (r.TakeIf('>'))
@ -325,11 +327,11 @@ namespace Avalonia.Markup.Parsers

        public class OfTypeSyntax : ISyntax, ITypeSyntax
        {
-            public string TypeName { get; set; }
+            public string TypeName { get; set; } = string.Empty;

            public string Xmlns { get; set; } = string.Empty;

-            public override bool Equals(object obj)
+            public override bool Equals(object? obj)
            {
                var other = obj as OfTypeSyntax;
                return other != null && other.TypeName == TypeName && other.Xmlns == Xmlns;
@ -338,11 +340,11 @@ namespace Avalonia.Markup.Parsers

        public class IsSyntax : ISyntax, ITypeSyntax
        {
-            public string TypeName { get; set; }
+            public string TypeName { get; set; } = string.Empty;

            public string Xmlns { get; set; } = string.Empty;

-            public override bool Equals(object obj)
+            public override bool Equals(object? obj)
            {
                var other = obj as IsSyntax;
                return other != null && other.TypeName == TypeName && other.Xmlns == Xmlns;
@ -351,9 +353,9 @@ namespace Avalonia.Markup.Parsers

        public class ClassSyntax : ISyntax
        {
-            public string Class { get; set; }
+            public string Class { get; set; } = string.Empty;

-            public override bool Equals(object obj)
+            public override bool Equals(object? obj)
            {
                return obj is ClassSyntax && ((ClassSyntax)obj).Class == Class;
            }
@ -361,9 +363,9 @@ namespace Avalonia.Markup.Parsers

        public class NameSyntax : ISyntax
        {
-            public string Name { get; set; }
+            public string Name { get; set; } = string.Empty;

-            public override bool Equals(object obj)
+            public override bool Equals(object? obj)
            {
                return obj is NameSyntax && ((NameSyntax)obj).Name == Name;
            }
@ -371,11 +373,11 @@ namespace Avalonia.Markup.Parsers

        public class PropertySyntax : ISyntax
        {
-            public string Property { get; set; }
+            public string Property { get; set; } = string.Empty;

-            public string Value { get; set; }
+            public string Value { get; set; } = string.Empty;

-            public override bool Equals(object obj)
+            public override bool Equals(object? obj)
            {
                return obj is PropertySyntax && 
                    ((PropertySyntax)obj).Property == Property && 
@ -385,7 +387,7 @@ namespace Avalonia.Markup.Parsers

        public class ChildSyntax : ISyntax
        {
-            public override bool Equals(object obj)
+            public override bool Equals(object? obj)
            {
                return obj is ChildSyntax;
            }
@ -393,7 +395,7 @@ namespace Avalonia.Markup.Parsers

        public class DescendantSyntax : ISyntax
        {
-            public override bool Equals(object obj)
+            public override bool Equals(object? obj)
            {
                return obj is DescendantSyntax;
            }
@ -401,7 +403,7 @@ namespace Avalonia.Markup.Parsers

        public class TemplateSyntax : ISyntax
        {
-            public override bool Equals(object obj)
+            public override bool Equals(object? obj)
            {
                return obj is TemplateSyntax;
            }
@ -409,9 +411,9 @@ namespace Avalonia.Markup.Parsers

        public class NotSyntax : ISyntax
        {
-            public IEnumerable<ISyntax> Argument { get; set; }
+            public IEnumerable<ISyntax> Argument { get; set; } = Enumerable.Empty<ISyntax>();

-            public override bool Equals(object obj)
+            public override bool Equals(object? obj)
            {
                return (obj is NotSyntax not) && Argument.SequenceEqual(not.Argument);
            }
@ -419,7 +421,7 @@ namespace Avalonia.Markup.Parsers

        public class CommaSyntax : ISyntax
        {
-            public override bool Equals(object obj)
+            public override bool Equals(object? obj)
            {
                return obj is CommaSyntax or;
            }
--- a/src/Markup/Avalonia.Markup/Markup/Parsers/SelectorParser.cs
+++ b/src/Markup/Avalonia.Markup/Markup/Parsers/SelectorParser.cs
@ -31,13 +31,13 @@ namespace Avalonia.Markup.Parsers
        /// </summary>
        /// <param name="s">The string.</param>
        /// <returns>The parsed selector.</returns>
-        public Selector Parse(string s)
+        public Selector? Parse(string s)
        {
            var syntax = SelectorGrammar.Parse(s);
            return Create(syntax);
        }

-        private Selector Create(IEnumerable<SelectorGrammar.ISyntax> syntax)
+        private Selector? Create(IEnumerable<SelectorGrammar.ISyntax> syntax)
        {
            var result = default(Selector);
            var results = default(List<Selector>);
@ -110,7 +110,7 @@ namespace Avalonia.Markup.Parsers
                            results = new List<Selector>();
                        }

-                        results.Add(result);
+                        results.Add(result ?? throw new NotSupportedException("Invalid selector!"));
                        result = null;
                        break;
                    default:
--- a/src/Skia/Avalonia.Skia/SKTypefaceCollection.cs
+++ b/src/Skia/Avalonia.Skia/SKTypefaceCollection.cs
@ -32,7 +32,7 @@ namespace Avalonia.Skia

            weight -= weight % 100; // make sure we start at a full weight

-            for (var i = (int)key.Style; i < 2; i++)
+            for (var i = 0; i < 2; i++)
            {
                // only try 2 font weights in each direction
                for (var j = 0; j < 200; j += 100)
@ -57,8 +57,8 @@ namespace Avalonia.Skia
                }
            }

-            //Nothing was found so we use the first typeface we can get.
-            return typefaces.Values.FirstOrDefault();
+            //Nothing was found so we try to get a regular typeface.
+            return typefaces.TryGetValue(new Typeface(key.FontFamily), out typeface) ? typeface : null;
        }
    }
 }
--- a/src/Windows/Avalonia.Direct2D1/Media/DrawingContextImpl.cs
+++ b/src/Windows/Avalonia.Direct2D1/Media/DrawingContextImpl.cs
@ -21,6 +21,7 @@ namespace Avalonia.Direct2D1.Media
        private readonly ILayerFactory _layerFactory;
        private readonly SharpDX.Direct2D1.RenderTarget _renderTarget;
        private readonly DeviceContext _deviceContext;
+        private readonly bool _ownsDeviceContext;
        private readonly SharpDX.DXGI.SwapChain1 _swapChain;
        private readonly Action _finishedCallback;

@ -51,10 +52,12 @@ namespace Avalonia.Direct2D1.Media
            if (_renderTarget is DeviceContext deviceContext)
            {
                _deviceContext = deviceContext;
+                _ownsDeviceContext = false;
            }
            else
            {
                _deviceContext = _renderTarget.QueryInterface<DeviceContext>();
+                _ownsDeviceContext = true;
            }

            _deviceContext.BeginDraw();
@ -96,6 +99,13 @@ namespace Avalonia.Direct2D1.Media
            {
                throw new RenderTargetCorruptedException(ex);
            }
+            finally
+            {
+                if (_ownsDeviceContext)
+                {
+                    _deviceContext.Dispose();
+                }
+            }
        }

        /// <summary>
@ -151,7 +161,7 @@ namespace Avalonia.Direct2D1.Media
            using (var d2dSource = ((BitmapImpl)source.Item).GetDirect2DBitmap(_deviceContext))
            using (var sourceBrush = new BitmapBrush(_deviceContext, d2dSource.Value))
            using (var d2dOpacityMask = CreateBrush(opacityMask, opacityMaskRect.Size))
-            using (var geometry = new SharpDX.Direct2D1.RectangleGeometry(_deviceContext.Factory, destRect.ToDirect2D()))
+            using (var geometry = new SharpDX.Direct2D1.RectangleGeometry(Direct2D1Platform.Direct2D1Factory, destRect.ToDirect2D()))
            {
                if (d2dOpacityMask.PlatformBrush != null)
                {
--- a/src/Windows/Avalonia.Direct2D1/Media/GeometryImpl.cs
+++ b/src/Windows/Avalonia.Direct2D1/Media/GeometryImpl.cs
@ -33,13 +33,13 @@ namespace Avalonia.Direct2D1.Media
        /// <inheritdoc/>
        public IGeometryImpl Intersect(IGeometryImpl geometry)
        {
-            var result = new PathGeometry(Geometry.Factory);
-
+            var result = new PathGeometry(Direct2D1Platform.Direct2D1Factory);
            using (var sink = result.Open())
            {
                Geometry.Combine(((GeometryImpl)geometry).Geometry, CombineMode.Intersect, sink);
-                return new StreamGeometryImpl(result);
+                sink.Close();
            }
+            return new StreamGeometryImpl(result);
        }

        /// <inheritdoc/>
--- a/src/Windows/Avalonia.Direct2D1/Media/Imaging/WicBitmapImpl.cs
+++ b/src/Windows/Avalonia.Direct2D1/Media/Imaging/WicBitmapImpl.cs
@ -13,7 +13,7 @@ namespace Avalonia.Direct2D1.Media
    /// </summary>
    public class WicBitmapImpl : BitmapImpl
    {
-        private BitmapDecoder _decoder;
+        private readonly BitmapDecoder _decoder;

        private static BitmapInterpolationMode ConvertInterpolationMode(Avalonia.Visuals.Media.Imaging.BitmapInterpolationMode interpolationMode)
        {
@ -41,7 +41,7 @@ namespace Avalonia.Direct2D1.Media
        /// <param name="fileName">The filename of the bitmap to load.</param>
        public WicBitmapImpl(string fileName)
        {
-            using (BitmapDecoder decoder = new BitmapDecoder(Direct2D1Platform.ImagingFactory, fileName, DecodeOptions.CacheOnDemand))
+            using (var decoder = new BitmapDecoder(Direct2D1Platform.ImagingFactory, fileName, DecodeOptions.CacheOnDemand))
            {
                WicImpl = new Bitmap(Direct2D1Platform.ImagingFactory, decoder.GetFrame(0), BitmapCreateCacheOption.CacheOnDemand);
                Dpi = new Vector(96, 96);
@ -177,7 +177,7 @@ namespace Avalonia.Direct2D1.Media
        /// <returns>The Direct2D bitmap.</returns>
        public override OptionalDispose<D2DBitmap> GetDirect2DBitmap(SharpDX.Direct2D1.RenderTarget renderTarget)
        {
-            FormatConverter converter = new FormatConverter(Direct2D1Platform.ImagingFactory);
+            using var converter = new FormatConverter(Direct2D1Platform.ImagingFactory);
            converter.Initialize(WicImpl, SharpDX.WIC.PixelFormat.Format32bppPBGRA);
            return new OptionalDispose<D2DBitmap>(D2DBitmap.FromWicBitmap(renderTarget, converter), true);
        }
--- a/src/Windows/Avalonia.Direct2D1/Media/StreamGeometryImpl.cs
+++ b/src/Windows/Avalonia.Direct2D1/Media/StreamGeometryImpl.cs
@ -29,9 +29,12 @@ namespace Avalonia.Direct2D1.Media
        public IStreamGeometryImpl Clone()
        {
            var result = new PathGeometry(Direct2D1Platform.Direct2D1Factory);
-            var sink = result.Open();
-            ((PathGeometry)Geometry).Stream(sink);
-            sink.Close();
+            using (var sink = result.Open())
+            {
+                ((PathGeometry)Geometry).Stream(sink);
+                sink.Close();
+            }
+
            return new StreamGeometryImpl(result);
        }

--- a/src/Windows/Avalonia.Direct2D1/PrimitiveExtensions.cs
+++ b/src/Windows/Avalonia.Direct2D1/PrimitiveExtensions.cs
@ -111,7 +111,7 @@ namespace Avalonia.Direct2D1
        /// <returns>The Direct2D brush.</returns>
        public static StrokeStyle ToDirect2DStrokeStyle(this Avalonia.Media.IPen pen, SharpDX.Direct2D1.RenderTarget renderTarget)
        {
-            return pen.ToDirect2DStrokeStyle(renderTarget.Factory);
+            return pen.ToDirect2DStrokeStyle(Direct2D1Platform.Direct2D1Factory);
        }

        /// <summary>
--- a/tests/Avalonia.Controls.UnitTests/MenuItemTests.cs
+++ b/tests/Avalonia.Controls.UnitTests/MenuItemTests.cs
@ -156,15 +156,35 @@ namespace Avalonia.Controls.UnitTests
            root.Child = null;
            Assert.Equal(0, command.SubscriptionCount);
        }
+        
+        [Fact]
+        public void MenuItem_Invokes_CanExecute_When_CommandParameter_Changed()
+        {
+            var command = new TestCommand(p => p is bool value && value);
+            var target = new MenuItem { Command = command };
+
+            target.CommandParameter = true;
+            Assert.True(target.IsEffectivelyEnabled);
+
+            target.CommandParameter = false;
+            Assert.False(target.IsEffectivelyEnabled);
+        }

        private class TestCommand : ICommand
        {
-            private bool _enabled;
+            private readonly Func<object, bool> _canExecute;
+            private readonly Action<object> _execute;
            private EventHandler _canExecuteChanged;

            public TestCommand(bool enabled = true)
+                : this(_ => enabled, _ => { })
+            {
+            }
+
+            public TestCommand(Func<object, bool> canExecute, Action<object> execute = null)
            {
-                _enabled = enabled;
+                _canExecute = canExecute;
+                _execute = execute ?? (_ => { });
            }

            public int SubscriptionCount { get; private set; }
@ -175,11 +195,9 @@ namespace Avalonia.Controls.UnitTests
                remove { _canExecuteChanged -= value; --SubscriptionCount; }
            }

-            public bool CanExecute(object parameter) => _enabled;
+            public bool CanExecute(object parameter) => _canExecute(parameter);

-            public void Execute(object parameter)
-            {
-            }
+            public void Execute(object parameter) => _execute(parameter);
        }
    }
 }
--- a/tests/Avalonia.Controls.UnitTests/Utils/HotKeyManagerTests.cs
+++ b/tests/Avalonia.Controls.UnitTests/Utils/HotKeyManagerTests.cs
@ -1,9 +1,14 @@
-using Moq;
+using System;
+using System.Collections.Generic;
+using Avalonia.Collections;
 using Avalonia.Controls.Presenters;
 using Avalonia.Controls.Templates;
+using Avalonia.Data;
 using Avalonia.Input;
 using Avalonia.Platform;
 using Avalonia.Styling;
+using Avalonia.UnitTests;
+using Moq;
 using Xunit;
 using System;
 using Avalonia.Input.Raw;
@ -53,7 +58,115 @@ namespace Avalonia.Controls.UnitTests.Utils

                HotKeyManager.SetHotKey(button, null);
                Assert.Empty(tl.KeyBindings);
+            }
+        }
+
+        [Fact]
+        public void HotKeyManager_Should_Release_Reference_When_Control_Detached()
+        {
+            using (AvaloniaLocator.EnterScope())
+            {
+                var styler = new Mock<Styler>();
+
+                AvaloniaLocator.CurrentMutable
+                    .Bind<IWindowingPlatform>().ToConstant(new WindowingPlatformMock())
+                    .Bind<IStyler>().ToConstant(styler.Object);
+
+                var gesture1 = new KeyGesture(Key.A, KeyModifiers.Control);
+
+                WeakReference reference = null;
+
+                var tl = new Window();

+                new Action(() =>
+                {
+                    var button = new Button();
+                    reference = new WeakReference(button, true);
+                    tl.Content = button;
+                    tl.Template = CreateWindowTemplate();
+                    tl.ApplyTemplate();
+                    tl.Presenter.ApplyTemplate();
+                    HotKeyManager.SetHotKey(button, gesture1);
+
+                    // Detach the button from the logical tree, so there is no reference to it
+                    tl.Content = null;
+                    tl.ApplyTemplate();
+                })();
+
+
+                // The button should be collected since it's detached from the listbox
+                GC.Collect();
+                GC.WaitForPendingFinalizers();
+                GC.Collect();
+                GC.WaitForPendingFinalizers();
+
+                Assert.Null(reference?.Target);
+            }
+        }
+
+        [Fact]
+        public void HotKeyManager_Should_Release_Reference_When_Control_In_Item_Template_Detached()
+        {
+            using (UnitTestApplication.Start(TestServices.StyledWindow))
+            {
+                var styler = new Mock<Styler>();
+
+                AvaloniaLocator.CurrentMutable
+                    .Bind<IWindowingPlatform>().ToConstant(new WindowingPlatformMock())
+                    .Bind<IStyler>().ToConstant(styler.Object);
+
+                var gesture1 = new KeyGesture(Key.A, KeyModifiers.Control);
+
+                var weakReferences = new List<WeakReference>();
+                var tl = new Window { SizeToContent = SizeToContent.WidthAndHeight, IsVisible = true };
+                var lm = tl.LayoutManager;
+
+                var keyGestures = new AvaloniaList<KeyGesture> { gesture1 };
+                var listBox = new ListBox
+                {
+                    Width = 100,
+                    Height = 100,
+                    VirtualizationMode = ItemVirtualizationMode.None,
+                    // Create a button with binding to the KeyGesture in the template and add it to references list
+                    ItemTemplate = new FuncDataTemplate(typeof(KeyGesture), (o, scope) =>
+                    {
+                        var keyGesture = o as KeyGesture;
+                        var button = new Button
+                        {
+                            DataContext = keyGesture, [!Button.HotKeyProperty] = new Binding("")
+                        };
+                        weakReferences.Add(new WeakReference(button, true));
+                        return button;
+                    })
+                };
+                // Add the listbox and render it
+                tl.Content = listBox;
+                lm.ExecuteInitialLayoutPass();
+                listBox.Items = keyGestures;
+                lm.ExecuteLayoutPass();
+
+                // Let the button detach when clearing the source items
+                keyGestures.Clear();
+                lm.ExecuteLayoutPass();
+                
+                // Add it again to double check,and render
+                keyGestures.Add(gesture1);
+                lm.ExecuteLayoutPass();
+                
+                keyGestures.Clear();
+                lm.ExecuteLayoutPass();
+                
+                // The button should be collected since it's detached from the listbox
+                GC.Collect();
+                GC.WaitForPendingFinalizers();
+                GC.Collect();
+                GC.WaitForPendingFinalizers();
+                
+                Assert.True(weakReferences.Count > 0);
+                foreach (var weakReference in weakReferences)
+                {
+                    Assert.Null(weakReference.Target);
+                }
            }
        }

--- a/tests/Avalonia.Markup.Xaml.UnitTests/Xaml/IgnoredDirectivesTests.cs
+++ b/tests/Avalonia.Markup.Xaml.UnitTests/Xaml/IgnoredDirectivesTests.cs
@ -0,0 +1,31 @@
+using Avalonia.Controls;
+using Avalonia.Controls.Presenters;
+using Avalonia.UnitTests;
+using Xunit;
+
+namespace Avalonia.Markup.Xaml.UnitTests.Xaml
+{
+    public class IgnoredDirectivesTests : XamlTestBase
+    {
+        [Fact]
+        public void Ignored_Directives_Should_Compile()
+        {
+            using (UnitTestApplication.Start(TestServices.StyledWindow))
+            {
+                const string xaml = @"
+<Window xmlns='https://github.com/avaloniaui'
+        xmlns:sys='clr-namespace:System;assembly=netstandard'
+        xmlns:x='http://schemas.microsoft.com/winfx/2006/xaml'>
+    <TextBlock x:Name='target' x:FieldModifier='Public' Text='Foo'/>
+</Window>";
+                var window = (Window)AvaloniaRuntimeXamlLoader.Load(xaml);
+                var target = window.FindControl<TextBlock>("target");
+
+                window.ApplyTemplate();
+                target.ApplyTemplate();
+
+                Assert.Equal("Foo", target.Text);
+            }
+        }
+    }
+}
--- a/tests/Avalonia.Skia.UnitTests/Media/CustomFontManagerImpl.cs
+++ b/tests/Avalonia.Skia.UnitTests/Media/CustomFontManagerImpl.cs
@ -48,7 +48,7 @@ namespace Avalonia.Skia.UnitTests.Media
                    continue;
                }

-                typeface = new Typeface(customTypeface.FontFamily.Name, fontStyle, fontWeight);
+                typeface = new Typeface(customTypeface.FontFamily, fontStyle, fontWeight);

                return true;
            }
@ -83,7 +83,7 @@ namespace Avalonia.Skia.UnitTests.Media
                case "Noto Mono":
                    {
                        var typefaceCollection = SKTypefaceCollectionCache.GetOrAddTypefaceCollection(_defaultTypeface.FontFamily);
-                        skTypeface = typefaceCollection.Get(typeface);
+                        skTypeface = typefaceCollection.Get(_defaultTypeface);
                        break;
                    }
                default:
--- a/tests/Avalonia.Skia.UnitTests/Media/SKTypefaceCollectionCacheTests.cs
+++ b/tests/Avalonia.Skia.UnitTests/Media/SKTypefaceCollectionCacheTests.cs
@ -7,25 +7,33 @@ namespace Avalonia.Skia.UnitTests.Media
    public class SKTypefaceCollectionCacheTests
    {
        [Fact]
-        public void Should_Load_Typefaces_From_Invalid_Name()
+        public void Should_Get_Near_Matching_Typeface()
        {
            using (UnitTestApplication.Start(TestServices.MockPlatformRenderInterface))
            {
                var notoMono =
                    new FontFamily("resm:Avalonia.Skia.UnitTests.Assets?assembly=Avalonia.Skia.UnitTests#Noto Mono");

-                var colorEmoji =
-                    new FontFamily("resm:Avalonia.Skia.UnitTests.Assets?assembly=Avalonia.Skia.UnitTests#Twitter Color Emoji");
-
                var notoMonoCollection = SKTypefaceCollectionCache.GetOrAddTypefaceCollection(notoMono);

-                var typeface = new Typeface("ABC", FontStyle.Italic, FontWeight.Bold);
-
-                Assert.Equal("Noto Mono", notoMonoCollection.Get(typeface).FamilyName);
-
-                var notoColorEmojiCollection = SKTypefaceCollectionCache.GetOrAddTypefaceCollection(colorEmoji);
+                Assert.Equal("Noto Mono",
+                    notoMonoCollection.Get(new Typeface(notoMono, weight: FontWeight.Bold)).FamilyName);
+            }
+        }
+        
+        [Fact]
+        public void Should_Get_Null_For_Invalid_FamilyName()
+        {
+            using (UnitTestApplication.Start(TestServices.MockPlatformRenderInterface))
+            {
+                var notoMono =
+                    new FontFamily("resm:Avalonia.Skia.UnitTests.Assets?assembly=Avalonia.Skia.UnitTests#Noto Mono");
+                
+                var notoMonoCollection = SKTypefaceCollectionCache.GetOrAddTypefaceCollection(notoMono);

-                Assert.Equal("Twitter Color Emoji", notoColorEmojiCollection.Get(typeface).FamilyName);
+                var typeface = notoMonoCollection.Get(new Typeface("ABC"));
+                
+                Assert.Null(typeface);
            }
        }
    }