Merge branch 'master' into binding-to-classes

build/ReactiveUI.props

@@ -1,5 +1,5 @@
 <Project DefaultTargets="Build" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
   <ItemGroup>
-    <PackageReference Include="ReactiveUI" Version="12.1.1" />
+    <PackageReference Include="ReactiveUI" Version="13.2.10" />
   </ItemGroup>
 </Project>

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

@@ -23,7 +23,7 @@ extern IAvnCursorFactory* CreateCursorFactory();
 extern IAvnGlDisplay* GetGlDisplay();
 extern IAvnMenu* CreateAppMenu(IAvnMenuEvents* events);
 extern IAvnMenuItem* CreateAppMenuItem();
-extern IAvnMenuItem* CreateAppMenuItemSeperator();
+extern IAvnMenuItem* CreateAppMenuItemSeparator();
 extern IAvnNativeControlHost* CreateNativeControlHost(NSView* parent);
 extern void SetAppMenu (NSString* appName, IAvnMenu* appMenu);
 extern IAvnMenu* GetAppMenu ();

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

@@ -253,9 +253,9 @@ public:
         return S_OK;
     }
     
-    virtual HRESULT CreateMenuItemSeperator (IAvnMenuItem** ppv) override
+    virtual HRESULT CreateMenuItemSeparator (IAvnMenuItem** ppv) override
     {
-        *ppv = ::CreateAppMenuItemSeperator();
+        *ppv = ::CreateAppMenuItemSeparator();
         return S_OK;
     }
     

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

@@ -31,13 +31,13 @@ private:
     NSMenuItem* _native; // here we hold a pointer to an AvnMenuItem
     IAvnActionCallback* _callback;
     IAvnPredicateCallback* _predicate;
-    bool _isSeperator;
+    bool _isSeparator;
     bool _isCheckable;
     
 public:
     FORWARD_IUNKNOWN()
     
-    AvnAppMenuItem(bool isSeperator);
+    AvnAppMenuItem(bool isSeparator);
     
     NSMenuItem* GetNative();
     

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

@@ -71,12 +71,12 @@
 }
 @end
 
-AvnAppMenuItem::AvnAppMenuItem(bool isSeperator)
+AvnAppMenuItem::AvnAppMenuItem(bool isSeparator)
 {
     _isCheckable = false;
-    _isSeperator = isSeperator;
+    _isSeparator = isSeparator;
     
-    if(isSeperator)
+    if(isSeparator)
     {
         _native = [NSMenuItem separatorItem];
     }
@@ -427,7 +427,7 @@ extern IAvnMenuItem* CreateAppMenuItem()
     }
 }
 
-extern IAvnMenuItem* CreateAppMenuItemSeperator()
+extern IAvnMenuItem* CreateAppMenuItemSeparator()
 {
     @autoreleasepool
     {

samples/ControlCatalog/MainWindow.xaml

@@ -18,11 +18,11 @@
       <NativeMenuItem Header="File">
         <NativeMenu>
           <NativeMenuItem Icon="/Assets/test_icon.ico" Header="Open" Clicked="OnOpenClicked" Gesture="Ctrl+O"/>
-          <NativeMenuItemSeperator/>
+          <NativeMenuItemSeperator/><!-- Uses incorrect spelling to demonstrate backwards compatibility -->
           <NativeMenuItem Icon="/Assets/github_icon.png" Header="Recent">
             <NativeMenu/>
           </NativeMenuItem>
-          <NativeMenuItemSeperator/>
+          <NativeMenuItemSeparator/>
           <NativeMenuItem Header="{x:Static local:MainWindow.MenuQuitHeader}"
                           Gesture="{x:Static local:MainWindow.MenuQuitGesture}"
                           Clicked="OnCloseClicked" />

src/Avalonia.Animation/Animatable.cs

@@ -2,6 +2,7 @@ using System;
 using System.Collections;
 using System.Collections.Generic;
 using System.Collections.Specialized;
+using System.Linq;
 using Avalonia.Data;
 
 #nullable enable
@@ -93,16 +94,35 @@ namespace Avalonia.Animation
                 var oldTransitions = change.OldValue.GetValueOrDefault<Transitions>();
                 var newTransitions = change.NewValue.GetValueOrDefault<Transitions>();
 
+                // When transitions are replaced, we add the new transitions before removing the old
+                // transitions, so that when the old transition being disposed causes the value to
+                // change, there is a corresponding entry in `_transitionStates`. This means that we
+                // need to account for any transitions present in both the old and new transitions
+                // collections.
                 if (newTransitions is object)
                 {
+                    var toAdd = (IList)newTransitions;
+
+                    if (newTransitions.Count > 0 && oldTransitions?.Count > 0)
+                    {
+                        toAdd = newTransitions.Except(oldTransitions).ToList();
+                    }
+
                     newTransitions.CollectionChanged += TransitionsCollectionChanged;
-                    AddTransitions(newTransitions);
+                    AddTransitions(toAdd);
                 }
 
                 if (oldTransitions is object)
                 {
+                    var toRemove = (IList)oldTransitions;
+
+                    if (oldTransitions.Count > 0 && newTransitions?.Count > 0)
+                    {
+                        toRemove = oldTransitions.Except(newTransitions).ToList();
+                    }
+
                     oldTransitions.CollectionChanged -= TransitionsCollectionChanged;
-                    RemoveTransitions(oldTransitions);
+                    RemoveTransitions(toRemove);
                 }
             }
             else if (_transitionsEnabled &&
@@ -115,9 +135,9 @@ namespace Avalonia.Animation
                 {
                     var transition = Transitions[i];
 
-                    if (transition.Property == change.Property)
+                    if (transition.Property == change.Property &&
+                        _transitionState.TryGetValue(transition, out var state))
                     {
-                        var state = _transitionState[transition];
                         var oldValue = state.BaseValue;
                         var newValue = GetAnimationBaseValue(transition.Property);
 

src/Avalonia.Base/PropertyStore/BindingEntry.cs

@@ -65,7 +65,6 @@ namespace Avalonia.PropertyStore
         {
             _subscription?.Dispose();
             _subscription = null;
-            _isSubscribed = false;
             OnCompleted();
         }
 
@@ -74,6 +73,7 @@ namespace Avalonia.PropertyStore
             var oldValue = _value;
             _value = default;
             Priority = BindingPriority.Unset;
+            _isSubscribed = false;
             _sink.Completed(Property, this, oldValue);
         }
 
@@ -104,8 +104,11 @@ namespace Avalonia.PropertyStore
         public void Start(bool ignoreBatchUpdate)
         {
             // We can't use _subscription to check whether we're subscribed because it won't be set
-            // until Subscribe has finished, which will be too late to prevent reentrancy.
-            if (!_isSubscribed && (!_batchUpdate || ignoreBatchUpdate))
+            // until Subscribe has finished, which will be too late to prevent reentrancy. In addition
+            // don't re-subscribe to completed/disposed bindings (indicated by Unset priority).
+            if (!_isSubscribed &&
+                Priority != BindingPriority.Unset &&
+                (!_batchUpdate || ignoreBatchUpdate))
             {
                 _isSubscribed = true;
                 _subscription = Source.Subscribe(this);

src/Avalonia.Base/PropertyStore/ConstantValueEntry.cs

@@ -6,12 +6,19 @@ using Avalonia.Data;
 
 namespace Avalonia.PropertyStore
 {
+    /// <summary>
+    /// Represents an untyped interface to <see cref="ConstantValueEntry{T}"/>.
+    /// </summary>
+    internal interface IConstantValueEntry : IPriorityValueEntry, IDisposable
+    {
+    }
+
     /// <summary>
     /// Stores a value with a priority in a <see cref="ValueStore"/> or
     /// <see cref="PriorityValue{T}"/>.
     /// </summary>
     /// <typeparam name="T">The property type.</typeparam>
-    internal class ConstantValueEntry<T> : IPriorityValueEntry<T>, IDisposable
+    internal class ConstantValueEntry<T> : IPriorityValueEntry<T>, IConstantValueEntry
     {
         private IValueSink _sink;
         private Optional<T> _value;

src/Avalonia.Base/Utilities/AvaloniaPropertyValueStore.cs

@@ -94,7 +94,7 @@ namespace Avalonia.Utilities
             return (0, false);
         }
 
-        public bool TryGetValue(AvaloniaProperty property, [MaybeNull] out TValue value)
+        public bool TryGetValue(AvaloniaProperty property, [MaybeNullWhen(false)] out TValue value)
         {
             (int index, bool found) = TryFindEntry(property.Id);
             if (!found)

src/Avalonia.Base/ValueStore.cs

@@ -1,5 +1,6 @@
 using System;
 using System.Collections.Generic;
+using System.Diagnostics.CodeAnalysis;
 using Avalonia.Data;
 using Avalonia.PropertyStore;
 using Avalonia.Utilities;
@@ -56,7 +57,7 @@ namespace Avalonia
 
         public bool IsAnimating(AvaloniaProperty property)
         {
-            if (_values.TryGetValue(property, out var slot))
+            if (TryGetValue(property, out var slot))
             {
                 return slot.Priority < BindingPriority.LocalValue;
             }
@@ -66,7 +67,7 @@ namespace Avalonia
 
         public bool IsSet(AvaloniaProperty property)
         {
-            if (_values.TryGetValue(property, out var slot))
+            if (TryGetValue(property, out var slot))
             {
                 return slot.GetValue().HasValue;
             }
@@ -79,7 +80,7 @@ namespace Avalonia
             BindingPriority maxPriority,
             out T value)
         {
-            if (_values.TryGetValue(property, out var slot))
+            if (TryGetValue(property, out var slot))
             {
                 var v = ((IValue<T>)slot).GetValue(maxPriority);
 
@@ -103,7 +104,7 @@ namespace Avalonia
 
             IDisposable? result = null;
 
-            if (_values.TryGetValue(property, out var slot))
+            if (TryGetValue(property, out var slot))
             {
                 result = SetExisting(slot, property, value, priority);
             }
@@ -138,7 +139,7 @@ namespace Avalonia
             IObservable<BindingValue<T>> source,
             BindingPriority priority)
         {
-            if (_values.TryGetValue(property, out var slot))
+            if (TryGetValue(property, out var slot))
             {
                 return BindExisting(slot, property, source, priority);
             }
@@ -160,7 +161,7 @@ namespace Avalonia
 
         public void ClearLocalValue<T>(StyledPropertyBase<T> property)
         {
-            if (_values.TryGetValue(property, out var slot))
+            if (TryGetValue(property, out var slot))
             {
                 if (slot is PriorityValue<T> p)
                 {
@@ -173,7 +174,7 @@ namespace Avalonia
                     // During batch update values can't be removed immediately because they're needed to raise
                     // a correctly-typed _sink.ValueChanged notification. They instead mark themselves for removal
                     // by setting their priority to Unset.
-                    if (_batchUpdate is null)
+                    if (!IsBatchUpdating())
                     {
                         _values.Remove(property);
                     }
@@ -198,7 +199,7 @@ namespace Avalonia
 
         public void CoerceValue<T>(StyledPropertyBase<T> property)
         {
-            if (_values.TryGetValue(property, out var slot))
+            if (TryGetValue(property, out var slot))
             {
                 if (slot is PriorityValue<T> p)
                 {
@@ -209,7 +210,7 @@ namespace Avalonia
 
         public Diagnostics.AvaloniaPropertyValue? GetDiagnostic(AvaloniaProperty property)
         {
-            if (_values.TryGetValue(property, out var slot))
+            if (TryGetValue(property, out var slot))
             {
                 var slotValue = slot.GetValue();
                 return new Diagnostics.AvaloniaPropertyValue(
@@ -242,6 +243,7 @@ namespace Avalonia
             IPriorityValueEntry entry,
             Optional<T> oldValue)
         {
+            // We need to include remove sentinels here so call `_values.TryGetValue` directly.
             if (_values.TryGetValue(property, out var slot) && slot == entry)
             {
                 if (_batchUpdate is null)
@@ -285,7 +287,7 @@ namespace Avalonia
                 else
                 {
                     var priorityValue = new PriorityValue<T>(_owner, property, this, l);
-                    if (_batchUpdate is object)
+                    if (IsBatchUpdating())
                         priorityValue.BeginBatchUpdate();
                     result = priorityValue.SetValue(value, priority);
                     _values.SetValue(property, priorityValue);
@@ -311,7 +313,7 @@ namespace Avalonia
             {
                 priorityValue = new PriorityValue<T>(_owner, property, this, e);
 
-                if (_batchUpdate is object)
+                if (IsBatchUpdating())
                 {
                     priorityValue.BeginBatchUpdate();
                 }
@@ -338,7 +340,7 @@ namespace Avalonia
         private void AddValue(AvaloniaProperty property, IValue value)
         {
             _values.AddValue(property, value);
-            if (_batchUpdate is object && value is IBatchUpdate batch)
+            if (IsBatchUpdating() && value is IBatchUpdate batch)
                 batch.BeginBatchUpdate();
             value.Start();
         }
@@ -364,6 +366,21 @@ namespace Avalonia
             }
         }
 
+        private bool IsBatchUpdating() => _batchUpdate?.IsBatchUpdating == true;
+
+        private bool TryGetValue(AvaloniaProperty property, [MaybeNullWhen(false)] out IValue value)
+        {
+            return _values.TryGetValue(property, out value) && !IsRemoveSentinel(value);
+        }
+
+        private static bool IsRemoveSentinel(IValue value)
+        {
+            // Local value entries are optimized and contain only a single value field to save space,
+            // so there's no way to mark them for removal at the end of a batch update. Instead a
+            // ConstantValueEntry with a priority of Unset is used as a sentinel value.
+            return value is IConstantValueEntry t && t.Priority == BindingPriority.Unset;
+        }
+
         private class BatchUpdate
         {
             private ValueStore _owner;
@@ -373,6 +390,8 @@ namespace Avalonia
 
             public BatchUpdate(ValueStore owner) => _owner = owner;
 
+            public bool IsBatchUpdating => _batchUpdateCount > 0;
+
             public void Begin()
             {
                 if (_batchUpdateCount++ == 0)
@@ -437,8 +456,10 @@ namespace Avalonia
 
                             // During batch update values can't be removed immediately because they're needed to raise
                             // the _sink.ValueChanged notification. They instead mark themselves for removal by setting
-                            // their priority to Unset.
-                            if (slot.Priority == BindingPriority.Unset)
+                            // their priority to Unset. We need to re-read the slot here because raising ValueChanged
+                            // could have caused it to be updated.
+                            if (values.TryGetValue(entry.property, out var updatedSlot) &&
+                                updatedSlot.Priority == BindingPriority.Unset)
                             {
                                 values.Remove(entry.property);
                             }

src/Avalonia.Controls/Button.cs

@@ -218,6 +218,7 @@ namespace Avalonia.Controls
             if (Command != null)
             {
                 Command.CanExecuteChanged += CanExecuteChanged;
+                CanExecuteChanged(this, EventArgs.Empty);
             }
         }
 

src/Avalonia.Controls/NativeMenuItemSeparator.cs

@@ -0,0 +1,16 @@
+using System;
+
+namespace Avalonia.Controls
+{
+
+    [Obsolete("This class exists to maintain backwards compatiblity with existing code. Use NativeMenuItemSeparator instead")]
+    public class NativeMenuItemSeperator : NativeMenuItemSeparator 
+    {
+    }
+
+    public class NativeMenuItemSeparator : NativeMenuItemBase
+    {
+        [Obsolete("This is a temporary hack to make our MenuItem recognize this as a separator, don't use", true)]
+        public string Header => "-";
+    }
+}

src/Avalonia.Controls/NativeMenuItemSeperator.cs

@@ -1,10 +0,0 @@
-using System;
-
-namespace Avalonia.Controls
-{
-    public class NativeMenuItemSeperator : NativeMenuItemBase
-    {
-        [Obsolete("This is a temporary hack to make our MenuItem recognize this as a separator, don't use", true)]
-        public string Header => "-";
-    }
-}

src/Avalonia.Controls/Primitives/SelectingItemsControl.cs

@@ -64,7 +64,7 @@ namespace Avalonia.Controls.Primitives
                 nameof(SelectedItem),
                 o => o.SelectedItem,
                 (o, v) => o.SelectedItem = v,
-                defaultBindingMode: BindingMode.TwoWay);
+                defaultBindingMode: BindingMode.TwoWay, enableDataValidation: true);
 
         /// <summary>
         /// Defines the <see cref="SelectedItems"/> property.
@@ -466,6 +466,20 @@ namespace Avalonia.Controls.Primitives
             EndUpdating();
         }
 
+        /// <summary>
+        /// Called to update the validation state for properties for which data validation is
+        /// enabled.
+        /// </summary>
+        /// <param name="property">The property.</param>
+        /// <param name="value">The new binding value for the property.</param>
+        protected override void UpdateDataValidation<T>(AvaloniaProperty<T> property, BindingValue<T> value)
+        {
+            if (property == SelectedItemProperty)
+            {
+                DataValidationErrors.SetError(this, value.Error);
+            }
+        }
+        
         protected override void OnInitialized()
         {
             base.OnInitialized();
@@ -707,7 +721,7 @@ namespace Avalonia.Controls.Primitives
                 _oldSelectedItem = SelectedItem;
             }
             else if (e.PropertyName == nameof(InternalSelectionModel.WritableSelectedItems) &&
-                _oldSelectedItems != (Selection as InternalSelectionModel)?.SelectedItems)
+                     _oldSelectedItems != (Selection as InternalSelectionModel)?.SelectedItems)
             {
                 RaisePropertyChanged(
                     SelectedItemsProperty,
@@ -977,7 +991,7 @@ namespace Avalonia.Controls.Primitives
             public Optional<ISelectionModel> Selection { get; set; }
             public Optional<IList?> SelectedItems { get; set; }
 
-            public Optional<int> SelectedIndex 
+            public Optional<int> SelectedIndex
             {
                 get => _selectedIndex;
                 set
@@ -996,6 +1010,6 @@ namespace Avalonia.Controls.Primitives
                     _selectedIndex = default;
                 }
             }
-       }
+        }
     }
 }

src/Avalonia.FreeDesktop/DBusMenuExporter.cs

@@ -192,7 +192,7 @@ namespace Avalonia.FreeDesktop
             {
                 var (it, menu) = i;
 
-                if (it is NativeMenuItemSeperator)
+                if (it is NativeMenuItemSeparator)
                 {
                     if (name == "type")
                         return "separator";

src/Avalonia.Native/IAvnMenu.cs

@@ -125,8 +125,8 @@ namespace Avalonia.Native.Interop.Impl
 
         private __MicroComIAvnMenuItemProxy CreateNew(IAvaloniaNativeFactory factory, NativeMenuItemBase item)
         {
-            var nativeItem = (__MicroComIAvnMenuItemProxy)(item is NativeMenuItemSeperator ?
-                factory.CreateMenuItemSeperator() :
+            var nativeItem = (__MicroComIAvnMenuItemProxy)(item is NativeMenuItemSeparator ?
+                factory.CreateMenuItemSeparator() :
                 factory.CreateMenuItem());
             nativeItem.ManagedMenuItem = item;
 

src/Avalonia.Native/avn.idl

@@ -417,7 +417,7 @@ interface IAvaloniaNativeFactory : IUnknown
      HRESULT SetAppMenu(IAvnMenu* menu);
      HRESULT CreateMenu(IAvnMenuEvents* cb, IAvnMenu** ppv);
      HRESULT CreateMenuItem(IAvnMenuItem** ppv);
-     HRESULT CreateMenuItemSeperator(IAvnMenuItem** ppv);
+     HRESULT CreateMenuItemSeparator(IAvnMenuItem** ppv);
 }
 
 [uuid(233e094f-9b9f-44a3-9a6e-6948bbdd9fb1)]

src/Avalonia.ReactiveUI/AppBuilderExtensions.cs

@@ -9,18 +9,22 @@ namespace Avalonia.ReactiveUI
     {
         /// <summary>
         /// Initializes ReactiveUI framework to use with Avalonia. Registers Avalonia 
-        /// scheduler and Avalonia activation for view fetcher. Always remember to
-        /// call this method if you are using ReactiveUI in your application.
+        /// scheduler, an activation for view fetcher, a template binding hook. Remember
+        /// to call this method if you are using ReactiveUI in your application.
         /// </summary>
         public static TAppBuilder UseReactiveUI<TAppBuilder>(this TAppBuilder builder)
-            where TAppBuilder : AppBuilderBase<TAppBuilder>, new()
-        {
-            return builder.AfterPlatformServicesSetup(_ =>
+            where TAppBuilder : AppBuilderBase<TAppBuilder>, new() =>
+            builder.AfterPlatformServicesSetup(_ => Locator.RegisterResolverCallbackChanged(() =>
             {
+                if (Locator.CurrentMutable is null)
+                {
+                    return;
+                }
+
+                PlatformRegistrationManager.SetRegistrationNamespaces(RegistrationNamespace.Avalonia);
                 RxApp.MainThreadScheduler = AvaloniaScheduler.Instance;
                 Locator.CurrentMutable.RegisterConstant(new AvaloniaActivationForViewFetcher(), typeof(IActivationForViewFetcher));
                 Locator.CurrentMutable.RegisterConstant(new AutoDataTemplateBindingHook(), typeof(IPropertyBindingHook));
-            });
-        }
+            }));
     }
 }

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

@@ -35,7 +35,7 @@
       <ItemsControl Items="{Binding}">
         <ItemsControl.ItemTemplate>
           <DataTemplate>
-            <TextBlock Text="{Binding Message}" Foreground="{DynamicResource SystemControlErrorTextForegroundBrush}" TextWrapping="Wrap" />
+            <TextBlock Text="{Binding }" Foreground="{DynamicResource SystemControlErrorTextForegroundBrush}" TextWrapping="Wrap" />
           </DataTemplate>
         </ItemsControl.ItemTemplate>
       </ItemsControl>

src/Markup/Avalonia.Markup.Xaml/Templates/DataTemplate.cs

@@ -30,7 +30,7 @@ namespace Avalonia.Markup.Xaml.Templates
 
         public IControl Build(object data, IControl existing)
         {
-            return existing ?? TemplateContent.Load(Content).Control;
+            return existing ?? TemplateContent.Load(Content)?.Control;
         }
     }
 }

src/Markup/Avalonia.Markup.Xaml/Templates/ItemsPanelTemplate.cs

@@ -10,8 +10,7 @@ namespace Avalonia.Markup.Xaml.Templates
         [TemplateContent]
         public object Content { get; set; }
 
-        public IPanel Build()
-                => (IPanel)TemplateContent.Load(Content).Control;
+        public IPanel Build() => (IPanel)TemplateContent.Load(Content)?.Control;
 
         object ITemplate.Build() => Build();
     }

src/Markup/Avalonia.Markup.Xaml/Templates/Template.cs

@@ -10,7 +10,7 @@ namespace Avalonia.Markup.Xaml.Templates
         [TemplateContent]
         public object Content { get; set; }
 
-        public IControl Build() => TemplateContent.Load(Content).Control;
+        public IControl Build() => TemplateContent.Load(Content)?.Control;
 
         object ITemplate.Build() => Build();
     }

src/Markup/Avalonia.Markup.Xaml/Templates/TemplateContent.cs

@@ -1,6 +1,4 @@
 using System;
-using Avalonia.Controls;
-using System.Collections.Generic;
 using Avalonia.Controls.Templates;
 
 namespace Avalonia.Markup.Xaml.Templates
@@ -14,6 +12,12 @@ namespace Avalonia.Markup.Xaml.Templates
             {
                 return (ControlTemplateResult)direct(null);
             }
+
+            if (templateContent is null)
+            {
+                return null;
+            }
+
             throw new ArgumentException(nameof(templateContent));
         }
     }

src/Markup/Avalonia.Markup.Xaml/Templates/TreeDataTemplate.cs

@@ -51,8 +51,12 @@ namespace Avalonia.Markup.Xaml.Templates
 
         public IControl Build(object data)
         {
-            var visualTreeForItem = TemplateContent.Load(Content).Control;
-            visualTreeForItem.DataContext = data;
+            var visualTreeForItem = TemplateContent.Load(Content)?.Control;
+            if (visualTreeForItem != null)
+            {
+                visualTreeForItem.DataContext = data;
+            }
+
             return visualTreeForItem;
         }
     }

tests/Avalonia.Animation.UnitTests/AnimatableTests.cs

@@ -330,6 +330,37 @@ namespace Avalonia.Animation.UnitTests
             }
         }
 
+        [Fact]
+        public void Transitions_Can_Be_Changed_To_Collection_That_Contains_The_Same_Transitions()
+        {
+            var target = CreateTarget();
+            var control = CreateControl(target.Object);
+
+            control.Transitions = new Transitions { target.Object };
+        }
+
+        [Fact]
+        public void Transitions_Can_Re_Set_During_Batch_Update()
+        {
+            var target = CreateTarget();
+            var control = CreateControl(target.Object);
+
+            // Assigning and then clearing Transitions ensures we have a transition state
+            // collection created.
+            control.Transitions = null;
+
+            control.BeginBatchUpdate();
+
+            // Setting opacity then Transitions means that we receive the Transitions change
+            // after the Opacity change when EndBatchUpdate is called.
+            control.Opacity = 0.5;
+            control.Transitions = new Transitions { target.Object };
+
+            // Which means that the transition state hasn't been initialized with the new
+            // Transitions when the Opacity change notification gets raised here.
+            control.EndBatchUpdate();
+        }
+
         private static Mock<ITransition> CreateTarget()
         {
             return CreateTransition(Visual.OpacityProperty);

tests/Avalonia.Base.UnitTests/AvaloniaObjectTests_BatchUpdate.cs

@@ -53,6 +53,21 @@ namespace Avalonia.Base.UnitTests
             Assert.Empty(raised);
         }
 
+        [Fact]
+        public void Binding_Disposal_Should_Not_Raise_Property_Changes_During_Batch_Update()
+        {
+            var target = new TestClass();
+            var observable = new TestObservable<string>("foo");
+            var raised = new List<string>();
+
+            var sub = target.Bind(TestClass.FooProperty, observable, BindingPriority.LocalValue);
+            target.GetObservable(TestClass.FooProperty).Skip(1).Subscribe(x => raised.Add(x));
+            target.BeginBatchUpdate();
+            sub.Dispose();
+
+            Assert.Empty(raised);
+        }
+
         [Fact]
         public void SetValue_Change_Should_Be_Raised_After_Batch_Update_1()
         {
@@ -240,6 +255,27 @@ namespace Avalonia.Base.UnitTests
             Assert.Equal(BindingPriority.Unset, raised[0].Priority);
         }
 
+        [Fact]
+        public void Binding_Disposal_Should_Be_Raised_After_Batch_Update()
+        {
+            var target = new TestClass();
+            var observable = new TestObservable<string>("foo");
+            var raised = new List<AvaloniaPropertyChangedEventArgs>();
+
+            var sub = target.Bind(TestClass.FooProperty, observable, BindingPriority.LocalValue);
+            target.PropertyChanged += (s, e) => raised.Add(e);
+
+            target.BeginBatchUpdate();
+            sub.Dispose();
+            target.EndBatchUpdate();
+
+            Assert.Equal(1, raised.Count);
+            Assert.Null(target.Foo);
+            Assert.Equal("foo", raised[0].OldValue);
+            Assert.Null(raised[0].NewValue);
+            Assert.Equal(BindingPriority.Unset, raised[0].Priority);
+        }
+
         [Fact]
         public void ClearValue_Change_Should_Be_Raised_After_Batch_Update_1()
         {
@@ -449,6 +485,92 @@ namespace Avalonia.Base.UnitTests
             Assert.Null(raised[1].NewValue);
         }
 
+        [Fact]
+        public void Can_Set_Cleared_Value_When_Ending_Batch_Update()
+        {
+            var target = new TestClass();
+            var raised = 0;
+
+            target.Foo = "foo";
+
+            target.BeginBatchUpdate();
+            target.ClearValue(TestClass.FooProperty);
+            target.PropertyChanged += (sender, e) =>
+            {
+                if (e.Property == TestClass.FooProperty && e.NewValue is null)
+                {
+                    target.Foo = "bar";
+                    ++raised;
+                }
+            };
+            target.EndBatchUpdate();
+
+            Assert.Equal("bar", target.Foo);
+            Assert.Equal(1, raised);
+        }
+
+        [Fact]
+        public void Can_Bind_Cleared_Value_When_Ending_Batch_Update()
+        {
+            var target = new TestClass();
+            var raised = 0;
+            var notifications = new List<AvaloniaPropertyChangedEventArgs>();
+
+            target.Foo = "foo";
+
+            target.BeginBatchUpdate();
+            target.ClearValue(TestClass.FooProperty);
+            target.PropertyChanged += (sender, e) =>
+            {
+                if (e.Property == TestClass.FooProperty && e.NewValue is null)
+                {
+                    target.Bind(TestClass.FooProperty, new TestObservable<string>("bar"));
+                    ++raised;
+                }
+
+                notifications.Add(e);
+            };
+            target.EndBatchUpdate();
+
+            Assert.Equal("bar", target.Foo);
+            Assert.Equal(1, raised);
+            Assert.Equal(2, notifications.Count);
+            Assert.Equal(null, notifications[0].NewValue);
+            Assert.Equal("bar", notifications[1].NewValue);
+        }
+
+        [Fact]
+        public void Can_Bind_Completed_Binding_Back_To_Original_Value_When_Ending_Batch_Update()
+        {
+            var target = new TestClass();
+            var raised = 0;
+            var notifications = new List<AvaloniaPropertyChangedEventArgs>();
+            var observable1 = new TestObservable<string>("foo");
+            var observable2 = new TestObservable<string>("foo");
+
+            target.Bind(TestClass.FooProperty, observable1);
+
+            target.BeginBatchUpdate();
+            observable1.OnCompleted();
+            target.PropertyChanged += (sender, e) =>
+            {
+                if (e.Property == TestClass.FooProperty && e.NewValue is null)
+                {
+                    target.Bind(TestClass.FooProperty, observable2);
+                    ++raised;
+                }
+
+                notifications.Add(e);
+            };
+            target.EndBatchUpdate();
+
+            Assert.Equal("foo", target.Foo);
+            Assert.Equal(1, raised);
+            Assert.Equal(2, notifications.Count);
+            Assert.Equal(null, notifications[0].NewValue);
+            Assert.Equal("foo", notifications[1].NewValue);
+        }
+
         public class TestClass : AvaloniaObject
         {
             public static readonly StyledProperty<string> FooProperty =

tests/Avalonia.Controls.UnitTests/CarouselTests.cs

@@ -1,10 +1,14 @@
 using System.Collections.ObjectModel;
 using System.Linq;
+using System.Reactive.Subjects;
 using Avalonia.Controls.Presenters;
 using Avalonia.Controls.Primitives;
 using Avalonia.Controls.Templates;
+using Avalonia.Data;
 using Avalonia.LogicalTree;
+using Avalonia.Threading;
 using Avalonia.VisualTree;
+using Avalonia.UnitTests;
 using Xunit;
 
 namespace Avalonia.Controls.UnitTests
@@ -77,9 +81,9 @@ namespace Avalonia.Controls.UnitTests
         {
             var items = new ObservableCollection<string>
             {
-               "Foo",
-               "Bar",
-               "FooBar"
+                "Foo",
+                "Bar",
+                "FooBar"
             };
 
             var target = new Carousel
@@ -113,9 +117,9 @@ namespace Avalonia.Controls.UnitTests
         {
             var items = new ObservableCollection<string>
             {
-               "Foo",
-               "Bar",
-               "FooBar"
+                "Foo",
+                "Bar",
+                "FooBar"
             };
 
             var target = new Carousel
@@ -172,9 +176,9 @@ namespace Avalonia.Controls.UnitTests
         {
             var items = new ObservableCollection<string>
             {
-               "Foo",
-               "Bar",
-               "FooBar"
+                "Foo",
+                "Bar",
+                "FooBar"
             };
 
             var target = new Carousel
@@ -206,9 +210,9 @@ namespace Avalonia.Controls.UnitTests
         {
             var items = new ObservableCollection<string>
             {
-               "Foo",
-               "Bar",
-               "FooBar"
+                "Foo",
+                "Bar",
+                "FooBar"
             };
 
             var target = new Carousel
@@ -235,9 +239,9 @@ namespace Avalonia.Controls.UnitTests
         {
             var items = new ObservableCollection<string>
             {
-               "Foo",
-               "Bar",
-               "FooBar"
+                "Foo",
+                "Bar",
+                "FooBar"
             };
 
             var target = new Carousel
@@ -269,9 +273,9 @@ namespace Avalonia.Controls.UnitTests
         {
             var items = new ObservableCollection<string>
             {
-               "Foo",
-               "Bar",
-               "FooBar"
+                "Foo",
+                "Bar",
+                "FooBar"
             };
 
             var target = new Carousel
@@ -311,5 +315,29 @@ namespace Avalonia.Controls.UnitTests
             contentPresenter.UpdateChild();
             return Assert.IsType<TextBlock>(contentPresenter.Child);
         }
+
+        [Fact]
+        public void SelectedItem_Validation()
+        {
+            using (UnitTestApplication.Start(TestServices.MockThreadingInterface))
+            {
+                var target = new Carousel
+                {
+                    Template = new FuncControlTemplate<Carousel>(CreateTemplate), IsVirtualized = false
+                };
+
+                target.ApplyTemplate();
+                target.Presenter.ApplyTemplate();
+
+                var exception = new System.InvalidCastException("failed validation");
+                var textObservable =
+                    new BehaviorSubject<BindingNotification>(new BindingNotification(exception,
+                        BindingErrorType.DataValidationError));
+                target.Bind(ComboBox.SelectedItemProperty, textObservable);
+
+                Assert.True(DataValidationErrors.GetHasErrors(target));
+                Assert.True(DataValidationErrors.GetErrors(target).SequenceEqual(new[] { exception }));
+            }
+        }
     }
 }

tests/Avalonia.Controls.UnitTests/ComboBoxTests.cs

@@ -1,11 +1,14 @@
 using System.Linq;
+using System.Reactive.Subjects;
 using Avalonia.Controls.Presenters;
 using Avalonia.Controls.Primitives;
 using Avalonia.Controls.Shapes;
 using Avalonia.Controls.Templates;
+using Avalonia.Data;
 using Avalonia.Input;
 using Avalonia.LogicalTree;
 using Avalonia.Media;
+using Avalonia.Threading;
 using Avalonia.UnitTests;
 using Xunit;
 
@@ -173,5 +176,31 @@ namespace Avalonia.Controls.UnitTests
                 Assert.Equal(expectedSelectedIndex, target.SelectedIndex);
             }
         }
+        
+        [Fact]
+        public void SelectedItem_Validation()
+        {
+
+            using (UnitTestApplication.Start(TestServices.MockThreadingInterface))
+            {
+                var target = new ComboBox
+                {
+                    Template = GetTemplate(),
+                    VirtualizationMode =  ItemVirtualizationMode.None
+                };
+
+                target.ApplyTemplate();
+                target.Presenter.ApplyTemplate();
+                
+                var exception = new System.InvalidCastException("failed validation");
+                var textObservable = new BehaviorSubject<BindingNotification>(new BindingNotification(exception, BindingErrorType.DataValidationError));
+                target.Bind(ComboBox.SelectedItemProperty, textObservable);
+
+                Assert.True(DataValidationErrors.GetHasErrors(target));
+                Assert.True(DataValidationErrors.GetErrors(target).SequenceEqual(new[] { exception }));
+                
+            }
+            
+        } 
     }
 }

tests/Avalonia.Controls.UnitTests/ListBoxTests.cs

@@ -1,11 +1,14 @@
 using System.Linq;
+using System.Reactive.Subjects;
 using Avalonia.Collections;
 using Avalonia.Controls.Presenters;
 using Avalonia.Controls.Primitives;
 using Avalonia.Controls.Templates;
+using Avalonia.Data;
 using Avalonia.Input;
 using Avalonia.LogicalTree;
 using Avalonia.Styling;
+using Avalonia.Threading;
 using Avalonia.UnitTests;
 using Avalonia.VisualTree;
 using Xunit;
@@ -559,5 +562,28 @@ namespace Avalonia.Controls.UnitTests
 
             public string Value { get; }
         }
+
+
+        [Fact]
+        public void SelectedItem_Validation()
+        {
+            var target = new ListBox
+            {
+                Template = ListBoxTemplate(),
+                Items = new[] { "Foo" },
+                ItemTemplate = new FuncDataTemplate<string>((_, __) => new Canvas()),
+                SelectionMode = SelectionMode.AlwaysSelected,
+                VirtualizationMode = ItemVirtualizationMode.None
+            };
+
+            Prepare(target);
+            
+            var exception = new System.InvalidCastException("failed validation");
+            var textObservable = new BehaviorSubject<BindingNotification>(new BindingNotification(exception, BindingErrorType.DataValidationError));
+            target.Bind(ComboBox.SelectedItemProperty, textObservable);
+                
+            Assert.True(DataValidationErrors.GetHasErrors(target));
+            Assert.True(DataValidationErrors.GetErrors(target).SequenceEqual(new[] { exception }));
+        }
     }
 }

tests/Avalonia.Markup.Xaml.UnitTests/Xaml/DataTemplateTests.cs

@@ -7,6 +7,31 @@ namespace Avalonia.Markup.Xaml.UnitTests.Xaml
 {
     public class DataTemplateTests : XamlTestBase
     {
+        [Fact]
+        public void DataTemplate_Can_Be_Empty()
+        {
+            using (UnitTestApplication.Start(TestServices.StyledWindow))
+            {
+                var xaml = @"
+<Window xmlns='https://github.com/avaloniaui'
+        xmlns:sys='clr-namespace:System;assembly=netstandard'
+        xmlns:x='http://schemas.microsoft.com/winfx/2006/xaml'>
+    <Window.DataTemplates>
+        <DataTemplate DataType='{x:Type sys:String}' />
+    </Window.DataTemplates>
+    <ContentControl Name='target' Content='Foo'/>
+</Window>";
+                var window = (Window)AvaloniaRuntimeXamlLoader.Load(xaml);
+                var target = window.FindControl<ContentControl>("target");
+
+                window.ApplyTemplate();
+                target.ApplyTemplate();
+                ((ContentPresenter)target.Presenter).UpdateChild();
+
+                Assert.Null(target.Presenter.Child);
+            }
+        }
+
         [Fact]
         public void DataTemplate_Can_Contain_Name()
         {