Merge branch 'master' into compiledbinding-methods

samples/ControlCatalog.NetCore/ControlCatalog.NetCore.csproj

@@ -6,6 +6,12 @@
     <TargetLatestRuntimePatch>true</TargetLatestRuntimePatch>
   </PropertyGroup>
 
+  <PropertyGroup Condition="'$(RunAotCompilation)' == 'true'">
+    <IlcTrimMetadata>true</IlcTrimMetadata>
+    <RestoreAdditionalProjectSources>https://pkgs.dev.azure.com/dnceng/public/_packaging/dotnet7/nuget/v3/index.json</RestoreAdditionalProjectSources>
+    <NativeAotCompilerVersion>7.0.0-*</NativeAotCompilerVersion>
+  </PropertyGroup>
+
   <ItemGroup>
     <ProjectReference Include="..\..\src\Avalonia.Headless.Vnc\Avalonia.Headless.Vnc.csproj" />
     <ProjectReference Include="..\..\src\Avalonia.Dialogs\Avalonia.Dialogs.csproj" />
@@ -15,6 +21,14 @@
     <PackageReference Include="Avalonia.Angle.Windows.Natives" Version="2.1.0.2020091801" />
   </ItemGroup>
 
+  <ItemGroup Condition="'$(RunAotCompilation)' == 'true'">
+    <PackageReference Include="Microsoft.DotNet.ILCompiler" Version="$(NativeAotCompilerVersion)" />
+    <!-- Cross-compilation for Windows x64-arm64 and Linux x64-arm64 -->
+    <PackageReference Condition="'$(RuntimeIdentifier)'=='win-arm64'" Include="runtime.win-x64.Microsoft.DotNet.ILCompiler" Version="$(NativeAotCompilerVersion)" />
+    <PackageReference Condition="'$(RuntimeIdentifier)'=='linux-arm64'" Include="runtime.linux-x64.Microsoft.DotNet.ILCompiler" Version="$(NativeAotCompilerVersion)" />
+    <RdXmlFile Include="rd.xml" />
+  </ItemGroup>
+
   <PropertyGroup>
     <!-- For Microsoft.CodeAnalysis -->
     <SatelliteResourceLanguages>en</SatelliteResourceLanguages>

samples/ControlCatalog.NetCore/rd.xml

@@ -0,0 +1,7 @@
+<Directives>
+  <Application>
+    <Assembly Name="ControlCatalog" Dynamic="Required All"></Assembly>
+    <Assembly Name="Avalonia.Themes.Default" Dynamic="Required All"></Assembly>
+    <Assembly Name="Avalonia.Themes.Fluent" Dynamic="Required All"></Assembly>
+  </Application>
+</Directives>

samples/ControlCatalog/MainView.xaml

@@ -40,6 +40,9 @@
       <TabItem Header="CheckBox">
         <pages:CheckBoxPage />
       </TabItem>
+      <TabItem Header="Clipboard">
+        <pages:ClipboardPage />
+      </TabItem>
       <TabItem Header="ComboBox">
         <pages:ComboBoxPage />
       </TabItem>

samples/ControlCatalog/Pages/ClipboardPage.xaml

@@ -0,0 +1,23 @@
+<UserControl x:Class="ControlCatalog.Pages.ClipboardPage"
+             xmlns="https://github.com/avaloniaui"
+             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+  <StackPanel Orientation="Vertical" Spacing="4">
+    <TextBlock Classes="h2">Example of ClipboardPage capabilities</TextBlock>
+
+    <Button Click="CopyText" Content="Copy text to clipboard" />
+    <Button Click="PasteText" Content="Paste text from clipboard" />
+    <Button Click="CopyTextDataObject" Content="Copy text to clipboard (data object)" />
+    <Button Click="PasteTextDataObject" Content="Paste text from clipboard (data object)" />
+
+    <Button Click="CopyFilesDataObject" Content="Copy files to clipboard (data object)" />
+    <Button Click="PasteFilesDataObject" Content="Paste files from clipboard (data object)" />
+
+    <Button Click="GetFormats" Content="Get clipboard formats" />
+    <Button Click="Clear" Content="Clear clipboard" />
+
+    <TextBox x:Name="ClipboardContent"
+             MinHeight="100"
+             AcceptsReturn="True"
+             Watermark="Text to copy of file names per line" />
+  </StackPanel>
+</UserControl>

samples/ControlCatalog/Pages/ClipboardPage.xaml.cs

@@ -0,0 +1,77 @@
+using System;
+using System.Collections.Generic;
+
+using Avalonia;
+using Avalonia.Controls;
+using Avalonia.Input;
+using Avalonia.Interactivity;
+using Avalonia.Markup.Xaml;
+
+namespace ControlCatalog.Pages
+{
+    public partial class ClipboardPage : UserControl
+    {
+        public ClipboardPage()
+        {
+            InitializeComponent();
+        }
+
+        private TextBox ClipboardContent => this.Get<TextBox>("ClipboardContent");
+
+        private void InitializeComponent()
+        {
+            AvaloniaXamlLoader.Load(this);
+        }
+
+        private async void CopyText(object sender, RoutedEventArgs args)
+        {
+            await Application.Current.Clipboard.SetTextAsync(ClipboardContent.Text);
+        }
+
+        private async void PasteText(object sender, RoutedEventArgs args)
+        {
+            ClipboardContent.Text = await Application.Current.Clipboard.GetTextAsync();
+        }
+
+        private async void CopyTextDataObject(object sender, RoutedEventArgs args)
+        {
+            var dataObject = new DataObject();
+            dataObject.Set(DataFormats.Text, ClipboardContent.Text ?? string.Empty);
+            await Application.Current.Clipboard.SetDataObjectAsync(dataObject);
+        }
+
+        private async void PasteTextDataObject(object sender, RoutedEventArgs args)
+        {
+            ClipboardContent.Text = await Application.Current.Clipboard.GetDataAsync(DataFormats.Text) as string ?? string.Empty;
+        }
+
+        private async void CopyFilesDataObject(object sender, RoutedEventArgs args)
+        {
+            var files = ClipboardContent.Text.Split(new[] { Environment.NewLine }, StringSplitOptions.RemoveEmptyEntries);
+            if (files.Length == 0)
+            {
+                return;
+            }
+            var dataObject = new DataObject();
+            dataObject.Set(DataFormats.FileNames, files);
+            await Application.Current.Clipboard.SetDataObjectAsync(dataObject);
+        }
+
+        private async void PasteFilesDataObject(object sender, RoutedEventArgs args)
+        {
+            var fiels = await Application.Current.Clipboard.GetDataAsync(DataFormats.FileNames) as IEnumerable<string>;
+            ClipboardContent.Text = fiels != null ? string.Join(Environment.NewLine, fiels) : string.Empty;
+        }
+
+        private async void GetFormats(object sender, RoutedEventArgs args)
+        {
+            var formats = await Application.Current.Clipboard.GetFormatsAsync();
+            ClipboardContent.Text = string.Join(Environment.NewLine, formats);
+        }
+
+        private async void Clear(object sender, RoutedEventArgs args)
+        {
+            await Application.Current.Clipboard.ClearAsync();
+        }
+    }
+}

samples/ControlCatalog/Pages/DragAndDropPage.xaml

@@ -11,7 +11,13 @@
                 Padding="16"
                 BorderBrush="{DynamicResource SystemAccentColor}"
                 BorderThickness="2">
-          <TextBlock Name="DragStateText" TextWrapping="Wrap">Drag Me</TextBlock>
+          <TextBlock Name="DragStateText" TextWrapping="Wrap">Drag Me (text)</TextBlock>
+        </Border>
+        <Border Name="DragMeFiles"
+                Padding="16"
+                BorderBrush="{DynamicResource SystemAccentColor}"
+                BorderThickness="2">
+          <TextBlock Name="DragStateFiles" TextWrapping="Wrap">Drag Me (files)</TextBlock>
         </Border>
         <Border Name="DragMeCustom"
                 Padding="16"

samples/ControlCatalog/Pages/DragAndDropPage.xaml.cs

@@ -2,11 +2,8 @@
 using Avalonia.Input;
 using Avalonia.Markup.Xaml;
 using System;
-using System.Collections.Generic;
-using System.IO;
 using System.Linq;
 using System.Reflection;
-using System.Text;
 
 namespace ControlCatalog.Pages
 {
@@ -24,6 +21,7 @@ namespace ControlCatalog.Pages
                 $"Text was dragged {++textCount} times"), DragDropEffects.Copy | DragDropEffects.Move | DragDropEffects.Link);
 
             SetupDnd("Custom", d => d.Set(CustomFormat, "Test123"), DragDropEffects.Move);
+            SetupDnd("Files", d => d.Set(DataFormats.FileNames, new[] { Assembly.GetEntryAssembly()?.GetModules().FirstOrDefault()?.FullyQualifiedName }), DragDropEffects.Copy);
         }
 
         void SetupDnd(string suffix, Action<DataObject> factory, DragDropEffects effects)

src/Avalonia.Controls/Calendar/CalendarDatePicker.cs

@@ -186,7 +186,8 @@ namespace Avalonia.Controls
                 nameof(SelectedDate),
                 o => o.SelectedDate,
                 (o, v) => o.SelectedDate = v,
-                enableDataValidation: true);
+                enableDataValidation: true, 
+                defaultBindingMode:BindingMode.TwoWay);
 
         public static readonly StyledProperty<CalendarDatePickerFormat> SelectedDateFormatProperty =
             AvaloniaProperty.Register<CalendarDatePicker, CalendarDatePickerFormat>(

src/Avalonia.Controls/DateTimePickers/DatePicker.cs

@@ -4,6 +4,7 @@ using Avalonia.Controls.Shapes;
 using Avalonia.Controls.Templates;
 using Avalonia.Data;
 using Avalonia.Interactivity;
+using Avalonia.Layout;
 using System;
 using System.Collections.Generic;
 using System.Globalization;
@@ -398,18 +399,27 @@ namespace Avalonia.Controls
         private void OnFlyoutButtonClicked(object? sender, RoutedEventArgs e)
         {
             if (_presenter == null)
-                throw new InvalidOperationException("No DatePickerPresenter found");
+                throw new InvalidOperationException("No DatePickerPresenter found.");
+            if (_popup == null)
+                throw new InvalidOperationException("No Popup found.");
 
             _presenter.Date = SelectedDate ?? DateTimeOffset.Now;
 
-            _popup!.IsOpen = true;
+            _popup.PlacementMode = PlacementMode.AnchorAndGravity;
+            _popup.PlacementAnchor = Primitives.PopupPositioning.PopupAnchor.Bottom;
+            _popup.PlacementGravity = Primitives.PopupPositioning.PopupGravity.Bottom;
+            _popup.PlacementConstraintAdjustment = Primitives.PopupPositioning.PopupPositionerConstraintAdjustment.SlideY;
+            _popup.IsOpen = true;
+
+            // Overlay popup hosts won't get measured until the next layout pass, but we need the
+            // template to be applied to `_presenter` now. Detect this case and force a layout pass.
+            if (!_presenter.IsMeasureValid)
+                (VisualRoot as ILayoutRoot)?.LayoutManager?.ExecuteInitialLayoutPass();
 
             var deltaY = _presenter.GetOffsetForPopup();
 
             // The extra 5 px I think is related to default popup placement behavior
-            _popup!.Host!.ConfigurePosition(_popup.PlacementTarget!, PlacementMode.AnchorAndGravity, new Point(0, deltaY + 5),
+            _popup.VerticalOffset = deltaY + 5;
-                Primitives.PopupPositioning.PopupAnchor.Bottom, Primitives.PopupPositioning.PopupGravity.Bottom,
-                 Primitives.PopupPositioning.PopupPositionerConstraintAdjustment.SlideY);
         }
 
         protected virtual void OnSelectedDateChanged(object? sender, DatePickerSelectedValueChangedEventArgs e)

src/Avalonia.Controls/DateTimePickers/DatePickerPresenter.cs

@@ -537,8 +537,11 @@ namespace Avalonia.Controls
 
         internal double GetOffsetForPopup()
         {
+            if (_monthSelector is null)
+                return 0;
+
             var acceptDismissButtonHeight = _acceptButton != null ? _acceptButton.Bounds.Height : 41;
-            return -(MaxHeight - acceptDismissButtonHeight) / 2 - (_monthSelector!.ItemHeight / 2);
+            return -(MaxHeight - acceptDismissButtonHeight) / 2 - (_monthSelector.ItemHeight / 2);
         }
     }
 }

src/Avalonia.Controls/DateTimePickers/TimePicker.cs

@@ -3,6 +3,7 @@ using Avalonia.Controls.Primitives;
 using Avalonia.Controls.Shapes;
 using Avalonia.Controls.Templates;
 using Avalonia.Data;
+using Avalonia.Layout;
 using System;
 using System.Globalization;
 
@@ -254,16 +255,28 @@ namespace Avalonia.Controls
 
         private void OnFlyoutButtonClicked(object? sender, Interactivity.RoutedEventArgs e)
         {
-            _presenter!.Time = SelectedTime ?? DateTime.Now.TimeOfDay;
+            if (_presenter == null)
+                throw new InvalidOperationException("No DatePickerPresenter found.");
+            if (_popup == null)
+                throw new InvalidOperationException("No Popup found.");
 
-            _popup!.IsOpen = true;
+            _presenter.Time = SelectedTime ?? DateTime.Now.TimeOfDay;
+
+            _popup.PlacementMode = PlacementMode.AnchorAndGravity;
+            _popup.PlacementAnchor = Primitives.PopupPositioning.PopupAnchor.Bottom;
+            _popup.PlacementGravity = Primitives.PopupPositioning.PopupGravity.Bottom;
+            _popup.PlacementConstraintAdjustment = Primitives.PopupPositioning.PopupPositionerConstraintAdjustment.SlideY;
+            _popup.IsOpen = true;
+
+            // Overlay popup hosts won't get measured until the next layout pass, but we need the
+            // template to be applied to `_presenter` now. Detect this case and force a layout pass.
+            if (!_presenter.IsMeasureValid)
+                (VisualRoot as ILayoutRoot)?.LayoutManager?.ExecuteInitialLayoutPass();
 
             var deltaY = _presenter.GetOffsetForPopup();
 
             // The extra 5 px I think is related to default popup placement behavior
-            _popup.Host!.ConfigurePosition(_popup.PlacementTarget!, PlacementMode.AnchorAndGravity, new Point(0, deltaY + 5),
+            _popup.VerticalOffset = deltaY + 5;
-                Primitives.PopupPositioning.PopupAnchor.Bottom, Primitives.PopupPositioning.PopupGravity.Bottom,
-                 Primitives.PopupPositioning.PopupPositionerConstraintAdjustment.SlideY);
         }
 
         private void OnDismissPicker(object? sender, EventArgs e)

src/Avalonia.Controls/DateTimePickers/TimePickerPresenter.cs

@@ -256,8 +256,11 @@ namespace Avalonia.Controls
 
         internal double GetOffsetForPopup()
         {
+            if (_hourSelector is null)
+                return 0;
+
             var acceptDismissButtonHeight = _acceptButton != null ? _acceptButton.Bounds.Height : 41;
-            return -(MaxHeight - acceptDismissButtonHeight) / 2 - (_hourSelector!.ItemHeight / 2);
+            return -(MaxHeight - acceptDismissButtonHeight) / 2 - (_hourSelector.ItemHeight / 2);
         }
     }
 }

src/Avalonia.MicroCom/CallbackBase.cs

@@ -0,0 +1,53 @@
+namespace Avalonia.MicroCom
+{
+    public abstract class CallbackBase : IUnknown, IMicroComShadowContainer
+    {
+        private readonly object _lock = new object();
+        private bool _referencedFromManaged = true;
+        private bool _referencedFromNative = false;
+        private bool _destroyed;
+
+        public bool IsDestroyed => _destroyed;
+
+        protected virtual void Destroyed()
+        {
+
+        }
+
+        public void Dispose()
+        {
+            lock (_lock)
+            {
+                _referencedFromManaged = false;
+                DestroyIfNeeded();
+            }
+        }
+
+        void DestroyIfNeeded()
+        {
+            if(_destroyed)
+                return;
+            if (_referencedFromManaged == false && _referencedFromNative == false)
+            {
+                _destroyed = true;
+                Destroyed();
+            }
+        }
+
+        public MicroComShadow Shadow { get; set; }
+        public void OnReferencedFromNative()
+        {
+            lock (_lock) 
+                _referencedFromNative = true;
+        }
+
+        public void OnUnreferencedFromNative()
+        {
+            lock (_lock)
+            {
+                _referencedFromNative = false;
+                DestroyIfNeeded();
+            }
+        }
+    }
+}

src/Avalonia.MicroCom/MicroComRuntime.cs

@@ -12,6 +12,8 @@ namespace Avalonia.MicroCom
             new ConcurrentDictionary<Type, Func<IntPtr, bool, object>>();
         private static ConcurrentDictionary<Type, Guid> _guids = new ConcurrentDictionary<Type, Guid>();
         private static ConcurrentDictionary<Guid, Type> _guidsToTypes = new ConcurrentDictionary<Guid, Type>();
+
+        internal static readonly Guid ManagedObjectInterfaceGuid = Guid.Parse("cd7687c0-a9c2-4563-b08e-a399df50c633");
         
         static MicroComRuntime()
         {
@@ -82,6 +84,19 @@ namespace Avalonia.MicroCom
             return shadow.Target;
         }
 
+        public static bool IsComWrapper(IUnknown obj) => obj is MicroComProxyBase;
+
+        public static object TryUnwrapManagedObject(IUnknown obj)
+        {
+            if (obj is not MicroComProxyBase proxy)
+                return null;
+            if (proxy.QueryInterface(ManagedObjectInterfaceGuid, out _) != 0)
+                return null;
+            // Successful QueryInterface always increments ref counter
+            proxy.Release();
+            return GetObjectFromCcw(proxy.NativePointer);
+        }
+
         public static bool TryGetTypeForGuid(Guid guid, out Type t) => _guidsToTypes.TryGetValue(guid, out t);
 
         public static bool GetVtableFor(Type type, out IntPtr ptr) => _vtables.TryGetValue(type, out ptr);

src/Avalonia.MicroCom/MicroComShadow.cs

@@ -23,6 +23,12 @@ namespace Avalonia.MicroCom
         {
             if (MicroComRuntime.TryGetTypeForGuid(*guid, out var type))
                 return QueryInterface(type, ppv);
+            else if (*guid == MicroComRuntime.ManagedObjectInterfaceGuid)
+            {
+                ccw->RefCount++;
+                *ppv = ccw;
+                return 0;
+            }
             else
                 return unchecked((int)0x80004002u);
         }

src/Avalonia.Native/AvaloniaNativeApplicationPlatform.cs

@@ -6,7 +6,7 @@ using Avalonia.Platform;
 
 namespace Avalonia.Native
 {
-    internal class AvaloniaNativeApplicationPlatform : CallbackBase, IAvnApplicationEvents, IPlatformLifetimeEventsImpl
+    internal class AvaloniaNativeApplicationPlatform : NativeCallbackBase, IAvnApplicationEvents, IPlatformLifetimeEventsImpl
     {
         public event EventHandler<ShutdownRequestedEventArgs> ShutdownRequested;
         

src/Avalonia.Native/AvaloniaNativeDragSource.cs

@@ -30,7 +30,7 @@ namespace Avalonia.Native
             return visual.VisualRoot as TopLevel;
         }
 
-        class DndCallback : CallbackBase, IAvnDndResultCallback
+        class DndCallback : NativeCallbackBase, IAvnDndResultCallback
         {
             private TaskCompletionSource<DragDropEffects> _tcs;
 

src/Avalonia.Native/AvaloniaNativePlatform.cs

@@ -79,7 +79,7 @@ namespace Avalonia.Native
             _factory = factory;
         }
 
-        class GCHandleDeallocator : CallbackBase, IAvnGCHandleDeallocatorCallback
+        class GCHandleDeallocator : NativeCallbackBase, IAvnGCHandleDeallocatorCallback
         {
             public void FreeGCHandle(IntPtr handle)
             {

src/Avalonia.Native/CallbackBase.cs

@@ -5,19 +5,8 @@ using Avalonia.Platform;
 
 namespace Avalonia.Native
 {
-    public class CallbackBase : IUnknown, IMicroComShadowContainer, IMicroComExceptionCallback
+    public abstract class NativeCallbackBase : CallbackBase, IMicroComExceptionCallback
     {
-        private readonly object _lock = new object();
-        private bool _referencedFromManaged = true;
-        private bool _referencedFromNative = false;
-        private bool _destroyed;
-        
-
-        protected virtual void Destroyed()
-        {
-
-        }
-
         public void RaiseException(Exception e)
         {
             if (AvaloniaLocator.Current.GetService<IPlatformThreadingInterface>() is PlatformThreadingInterface threadingInterface)
@@ -27,41 +16,5 @@ namespace Avalonia.Native
                 threadingInterface.DispatchException(ExceptionDispatchInfo.Capture(e));
             }
         }
-
-        public void Dispose()
-        {
-            lock (_lock)
-            {
-                _referencedFromManaged = false;
-                DestroyIfNeeded();
-            }
-        }
-
-        void DestroyIfNeeded()
-        {
-            if(_destroyed)
-                return;
-            if (_referencedFromManaged == false && _referencedFromNative == false)
-            {
-                _destroyed = true;
-                Destroyed();
-            }
-        }
-
-        public MicroComShadow Shadow { get; set; }
-        public void OnReferencedFromNative()
-        {
-            lock (_lock) 
-                _referencedFromNative = true;
-        }
-
-        public void OnUnreferencedFromNative()
-        {
-            lock (_lock)
-            {
-                _referencedFromNative = false;
-                DestroyIfNeeded();
-            }
-        }
     }
 }

src/Avalonia.Native/DeferredFramebuffer.cs

@@ -27,7 +27,7 @@ namespace Avalonia.Native
         public Vector Dpi { get; set; }
         public PixelFormat Format { get; set; }
 
-        class Disposer : CallbackBase
+        class Disposer : NativeCallbackBase
         {
             private IntPtr _ptr;
 

src/Avalonia.Native/IAvnMenu.cs

@@ -7,7 +7,7 @@ using Avalonia.Platform.Interop;
 
 namespace Avalonia.Native.Interop
 {
-    class MenuEvents : CallbackBase, IAvnMenuEvents
+    class MenuEvents : NativeCallbackBase, IAvnMenuEvents
     {
         private IAvnMenu _parent;
 

src/Avalonia.Native/MenuActionCallback.cs

@@ -3,7 +3,7 @@ using Avalonia.Native.Interop;
 
 namespace Avalonia.Native
 {
-    public class MenuActionCallback : CallbackBase, IAvnActionCallback
+    public class MenuActionCallback : NativeCallbackBase, IAvnActionCallback
     {
         private Action _action;
 

src/Avalonia.Native/PlatformThreadingInterface.cs

@@ -9,7 +9,7 @@ namespace Avalonia.Native
 {
     internal class PlatformThreadingInterface : IPlatformThreadingInterface
     {
-        class TimerCallback : CallbackBase, IAvnActionCallback
+        class TimerCallback : NativeCallbackBase, IAvnActionCallback
         {
             readonly Action _tick;
 
@@ -24,7 +24,7 @@ namespace Avalonia.Native
             }
         }
 
-        class SignaledCallback : CallbackBase, IAvnSignaledCallback
+        class SignaledCallback : NativeCallbackBase, IAvnSignaledCallback
         {
             readonly PlatformThreadingInterface _parent;
 

src/Avalonia.Native/PredicateCallback.cs

@@ -3,7 +3,7 @@ using Avalonia.Native.Interop;
 
 namespace Avalonia.Native
 {
-    public class PredicateCallback : CallbackBase, IAvnPredicateCallback
+    public class PredicateCallback : NativeCallbackBase, IAvnPredicateCallback
     {
         private Func<bool> _predicate;
 

src/Avalonia.Native/SystemDialogs.cs

@@ -62,7 +62,7 @@ namespace Avalonia.Native
         }
     }
 
-    internal unsafe class SystemDialogEvents : CallbackBase, IAvnSystemDialogEvents
+    internal unsafe class SystemDialogEvents : NativeCallbackBase, IAvnSystemDialogEvents
     {
         private TaskCompletionSource<string[]> _tcs;
 

src/Avalonia.Native/WindowImplBase.cs

@@ -151,7 +151,7 @@ namespace Avalonia.Native
         public IMouseDevice MouseDevice => _mouse;
         public abstract IPopupImpl CreatePopup();
 
-        protected unsafe class WindowBaseEvents : CallbackBase, IAvnWindowBaseEvents
+        protected unsafe class WindowBaseEvents : NativeCallbackBase, IAvnWindowBaseEvents
         {
             private readonly WindowBaseImpl _parent;
 

src/Avalonia.ReactiveUI/ReactiveUserControl.cs

@@ -48,6 +48,7 @@ namespace Avalonia.ReactiveUI
 
         protected override void OnDataContextChanged(EventArgs e)
         {
+            base.OnDataContextChanged(e);
             ViewModel = DataContext as TViewModel;
         }
 

src/Avalonia.Visuals/Animation/Animators/SolidColorBrushAnimator.cs

@@ -12,6 +12,8 @@ namespace Avalonia.Animation.Animators
     /// </summary>
     public class ISolidColorBrushAnimator : Animator<ISolidColorBrush?>
     {
+        private static readonly DoubleAnimator s_doubleAnimator = new DoubleAnimator();
+
         public override ISolidColorBrush? Interpolate(double progress, ISolidColorBrush? oldValue, ISolidColorBrush? newValue)
         {
             if (oldValue is null || newValue is null)
@@ -19,7 +21,9 @@ namespace Avalonia.Animation.Animators
                 return progress >= 0.5 ? newValue : oldValue;
             }
 
-            return new ImmutableSolidColorBrush(ColorAnimator.InterpolateCore(progress, oldValue.Color, newValue.Color));
+            return new ImmutableSolidColorBrush(
+                ColorAnimator.InterpolateCore(progress, oldValue.Color, newValue.Color),
+                s_doubleAnimator.Interpolate(progress, oldValue.Opacity, newValue.Opacity));
         }
 
         public override IDisposable BindAnimation(Animatable control, IObservable<ISolidColorBrush?> instance)

src/Windows/Avalonia.Win32/ClipboardFormats.cs

@@ -14,11 +14,11 @@ namespace Avalonia.Win32
 
         class ClipboardFormat
         {
-            public short Format { get; private set; }
+            public ushort Format { get; private set; }
             public string Name { get; private set; }
-            public short[] Synthesized { get; private set; }
+            public ushort[] Synthesized { get; private set; }
 
-            public ClipboardFormat(string name, short format, params short[] synthesized)
+            public ClipboardFormat(string name, ushort format, params ushort[] synthesized)
             {
                 Format = format;
                 Name = name;
@@ -28,12 +28,12 @@ namespace Avalonia.Win32
 
         private static readonly List<ClipboardFormat> FormatList = new List<ClipboardFormat>()
         {
-            new ClipboardFormat(DataFormats.Text, (short)UnmanagedMethods.ClipboardFormat.CF_UNICODETEXT, (short)UnmanagedMethods.ClipboardFormat.CF_TEXT),
+            new ClipboardFormat(DataFormats.Text, (ushort)UnmanagedMethods.ClipboardFormat.CF_UNICODETEXT, (ushort)UnmanagedMethods.ClipboardFormat.CF_TEXT),
-            new ClipboardFormat(DataFormats.FileNames, (short)UnmanagedMethods.ClipboardFormat.CF_HDROP),
+            new ClipboardFormat(DataFormats.FileNames, (ushort)UnmanagedMethods.ClipboardFormat.CF_HDROP),
         };
 
 
-        private static string QueryFormatName(short format)
+        private static string QueryFormatName(ushort format)
         {
             StringBuilder sb = new StringBuilder(MAX_FORMAT_NAME_LENGTH);
             if (UnmanagedMethods.GetClipboardFormatName(format, sb, sb.Capacity) > 0)
@@ -41,7 +41,7 @@ namespace Avalonia.Win32
             return null;
         }
 
-        public static string GetFormat(short format)
+        public static string GetFormat(ushort format)
         {
             lock (FormatList)
             {
@@ -58,7 +58,7 @@ namespace Avalonia.Win32
             }
         }
 
-        public static short GetFormat(string format)
+        public static ushort GetFormat(string format)
         {
             lock (FormatList)
             {
@@ -68,7 +68,7 @@ namespace Avalonia.Win32
                     int id = UnmanagedMethods.RegisterClipboardFormat(format);
                     if (id == 0)
                         throw new Win32Exception();
-                    pd = new ClipboardFormat(format, (short)id);
+                    pd = new ClipboardFormat(format, (ushort)id);
                     FormatList.Add(pd);
                 }
                 return pd.Format;

src/Windows/Avalonia.Win32/ClipboardImpl.cs

@@ -78,12 +78,13 @@ namespace Avalonia.Win32
         public async Task SetDataObjectAsync(IDataObject data)
         {
             Dispatcher.UIThread.VerifyAccess();
-            var wrapper = new DataObject(data);
+            using var wrapper = new DataObject(data);
             var i = OleRetryCount;
 
             while (true)
             {
-                var hr = UnmanagedMethods.OleSetClipboard(wrapper);
+                var ptr = MicroCom.MicroComRuntime.GetNativeIntPtr<Win32Com.IDataObject>(wrapper);
+                var hr = UnmanagedMethods.OleSetClipboard(ptr);
 
                 if (hr == 0)
                     break;
@@ -106,9 +107,9 @@ namespace Avalonia.Win32
 
                 if (hr == 0)
                 {
-                    var wrapper = new OleDataObject(dataObject);
+                    using var proxy = MicroCom.MicroComRuntime.CreateProxyFor<Win32Com.IDataObject>(dataObject, true);
+                    using var wrapper = new OleDataObject(proxy);
                     var formats = wrapper.GetDataFormats().ToArray();
-                    Marshal.ReleaseComObject(dataObject);
                     return formats;
                 }
 
@@ -130,9 +131,9 @@ namespace Avalonia.Win32
 
                 if (hr == 0)
                 {
-                    var wrapper = new OleDataObject(dataObject);
+                    using var proxy = MicroCom.MicroComRuntime.CreateProxyFor<Win32Com.IDataObject>(dataObject, true);
+                    using var wrapper = new OleDataObject(proxy);
                     var rv = wrapper.Get(format);
-                    Marshal.ReleaseComObject(dataObject);
                     return rv;
                 }
 

src/Windows/Avalonia.Win32/DataObject.cs

@@ -8,22 +8,25 @@ using System.Runtime.InteropServices;
 using System.Runtime.InteropServices.ComTypes;
 using System.Runtime.Serialization.Formatters.Binary;
 using Avalonia.Input;
+using Avalonia.MicroCom;
 using Avalonia.Win32.Interop;
+
+using FORMATETC = Avalonia.Win32.Interop.FORMATETC;
 using IDataObject = Avalonia.Input.IDataObject;
 
 namespace Avalonia.Win32
 {
-    class DataObject : IDataObject, IOleDataObject
+    internal sealed class DataObject : CallbackBase, IDataObject, Win32Com.IDataObject
     {
         // Compatibility with WinForms + WPF...
         internal static readonly byte[] SerializedObjectGUID = new Guid("FD9EA796-3B13-4370-A679-56106BB288FB").ToByteArray();
 
-        class FormatEnumerator : IEnumFORMATETC
+        class FormatEnumerator : CallbackBase, Win32Com.IEnumFORMATETC
         {
             private FORMATETC[] _formats;
-            private int _current;
+            private uint _current;
 
-            private FormatEnumerator(FORMATETC[] formats, int current)
+            private FormatEnumerator(FORMATETC[] formats, uint current)
             {
                 _formats = formats;
                 _current = current;
@@ -46,59 +49,70 @@ namespace Avalonia.Win32
                 return result;
             }
 
-            public void Clone(out IEnumFORMATETC newEnum)
+            public unsafe uint Next(uint celt, FORMATETC* rgelt, uint* results)
-            {
-                newEnum = new FormatEnumerator(_formats, _current);
-            }
-
-            public int Next(int celt, FORMATETC[] rgelt, int[] pceltFetched)
             {
                 if (rgelt == null)
-                    return unchecked((int)UnmanagedMethods.HRESULT.E_INVALIDARG);
+                    return (uint)UnmanagedMethods.HRESULT.E_INVALIDARG;
 
-                int i = 0;
+                uint i = 0;
                 while (i < celt && _current < _formats.Length)
                 {
                     rgelt[i] = _formats[_current];
                     _current++;
                     i++;
                 }
-                if (pceltFetched != null)
-                    pceltFetched[0] = i;
 
                 if (i != celt)
-                    return unchecked((int)UnmanagedMethods.HRESULT.S_FALSE);
+                    return (uint)UnmanagedMethods.HRESULT.S_FALSE;
-                return unchecked((int)UnmanagedMethods.HRESULT.S_OK);
+
+                // "results" parameter can be NULL if celt is 1.
+                if (celt != 1 || results != default)
+                    *results = i;
+                return 0;
+            }
+
+            public uint Skip(uint celt)
+            {
+                _current += Math.Min(celt, int.MaxValue - _current);
+                if (_current >= _formats.Length)
+                    return (uint)UnmanagedMethods.HRESULT.S_FALSE;
+                return 0;
             }
 
-            public int Reset()
+            public void Reset()
             {
                 _current = 0;
-                return unchecked((int)UnmanagedMethods.HRESULT.S_OK);
             }
 
-            public int Skip(int celt)
+            public Win32Com.IEnumFORMATETC Clone()
             {
-                _current += Math.Min(celt, int.MaxValue - _current);
+                return new FormatEnumerator(_formats, _current);
-                if (_current >= _formats.Length)
-                    return unchecked((int)UnmanagedMethods.HRESULT.S_FALSE);
-                return unchecked((int)UnmanagedMethods.HRESULT.S_OK);
             }
         }
 
-        private const int DV_E_TYMED = unchecked((int)0x80040069);
+        private const uint DV_E_TYMED = 0x80040069;
-        private const int DV_E_DVASPECT = unchecked((int)0x8004006B);
+        private const uint DV_E_DVASPECT = 0x8004006B;
-        private const int DV_E_FORMATETC = unchecked((int)0x80040064);
+        private const uint DV_E_FORMATETC = 0x80040064;
-        private const int OLE_E_ADVISENOTSUPPORTED = unchecked((int)0x80040003);
+        private const uint OLE_E_ADVISENOTSUPPORTED = 0x80040003;
-        private const int STG_E_MEDIUMFULL = unchecked((int)0x80030070);
+        private const uint STG_E_MEDIUMFULL = 0x80030070;
+
         private const int GMEM_ZEROINIT = 0x0040;
         private const int GMEM_MOVEABLE = 0x0002;
 
 
-        IDataObject _wrapped;
+        private IDataObject _wrapped;
-        
+
         public DataObject(IDataObject wrapped)
         {
+            if (wrapped == null)
+            {
+                throw new ArgumentNullException(nameof(wrapped));
+            }
+            if (_wrapped is DataObject || _wrapped is OleDataObject)
+            {
+                throw new InvalidOperationException();
+            }
+
             _wrapped = wrapped;
         }
 
@@ -131,123 +145,123 @@ namespace Avalonia.Win32
 
         #region IOleDataObject
 
-        int IOleDataObject.DAdvise(ref FORMATETC pFormatetc, ADVF advf, IAdviseSink adviseSink, out int connection)
+        unsafe int Win32Com.IDataObject.DAdvise(FORMATETC* pFormatetc, int advf, void* adviseSink)
         {
-            if (_wrapped is IOleDataObject ole)
+            if (_wrapped is Win32Com.IDataObject ole)
-                return ole.DAdvise(ref pFormatetc, advf, adviseSink, out connection);
+                return ole.DAdvise(pFormatetc, advf, adviseSink);
-            connection = 0;
+            return 0;
-            return OLE_E_ADVISENOTSUPPORTED;
         }
 
-        void IOleDataObject.DUnadvise(int connection)
+        void Win32Com.IDataObject.DUnadvise(int connection)
         {
-            if (_wrapped is IOleDataObject ole)
+            if (_wrapped is Win32Com.IDataObject ole)
                 ole.DUnadvise(connection);
-            Marshal.ThrowExceptionForHR(OLE_E_ADVISENOTSUPPORTED);
+            throw new COMException(nameof(OLE_E_ADVISENOTSUPPORTED), unchecked((int)OLE_E_ADVISENOTSUPPORTED));
         }
 
-        int IOleDataObject.EnumDAdvise(out IEnumSTATDATA enumAdvise)
+        unsafe void* Win32Com.IDataObject.EnumDAdvise()
         {
-            if (_wrapped is IOleDataObject ole)
+            if (_wrapped is Win32Com.IDataObject ole)
-                return ole.EnumDAdvise(out enumAdvise);
+                return ole.EnumDAdvise();
 
-            enumAdvise = null;
+            return null;
-            return OLE_E_ADVISENOTSUPPORTED;
         }
 
-        IEnumFORMATETC IOleDataObject.EnumFormatEtc(DATADIR direction)
+        Win32Com.IEnumFORMATETC Win32Com.IDataObject.EnumFormatEtc(int direction)
         {
-            if (_wrapped is IOleDataObject ole)
+            if (_wrapped is Win32Com.IDataObject ole)
                 return ole.EnumFormatEtc(direction);
-            if (direction == DATADIR.DATADIR_GET)
+            if ((DATADIR)direction == DATADIR.DATADIR_GET)
                 return new FormatEnumerator(_wrapped);
-            throw new NotSupportedException();
+            throw new COMException(nameof(UnmanagedMethods.HRESULT.E_NOTIMPL), unchecked((int)UnmanagedMethods.HRESULT.E_NOTIMPL));
         }
 
-        int IOleDataObject.GetCanonicalFormatEtc(ref FORMATETC formatIn, out FORMATETC formatOut)
+        unsafe FORMATETC Win32Com.IDataObject.GetCanonicalFormatEtc(FORMATETC* formatIn)
         {
-            if (_wrapped is IOleDataObject ole)
+            if (_wrapped is Win32Com.IDataObject ole)
-                return ole.GetCanonicalFormatEtc(ref formatIn, out formatOut);
+                return ole.GetCanonicalFormatEtc(formatIn);
 
-            formatOut = new FORMATETC();
+            var formatOut = new FORMATETC();
             formatOut.ptd = IntPtr.Zero;
-            return unchecked((int)UnmanagedMethods.HRESULT.E_NOTIMPL);
+
+            throw new COMException(nameof(UnmanagedMethods.HRESULT.E_NOTIMPL), unchecked((int)UnmanagedMethods.HRESULT.E_NOTIMPL));
         }
 
-        void IOleDataObject.GetData(ref FORMATETC format, out STGMEDIUM medium)
+        unsafe uint Win32Com.IDataObject.GetData(FORMATETC* format, Interop.STGMEDIUM* medium)
         {
-            if (_wrapped is IOleDataObject ole)
+            if (_wrapped is Win32Com.IDataObject ole)
             {
-                ole.GetData(ref format, out medium);
+                return ole.GetData(format, medium);
-                return;
             }
-            if(!format.tymed.HasAllFlags(TYMED.TYMED_HGLOBAL))
-                Marshal.ThrowExceptionForHR(DV_E_TYMED);
 
-            if (format.dwAspect != DVASPECT.DVASPECT_CONTENT)
+            if (!format->tymed.HasAllFlags(TYMED.TYMED_HGLOBAL))
-                Marshal.ThrowExceptionForHR(DV_E_DVASPECT);
+                return DV_E_TYMED;
+
+            if (format->dwAspect != DVASPECT.DVASPECT_CONTENT)
+                return DV_E_DVASPECT;
 
-            string fmt = ClipboardFormats.GetFormat(format.cfFormat);
+            string fmt = ClipboardFormats.GetFormat(format->cfFormat);
             if (string.IsNullOrEmpty(fmt) || !_wrapped.Contains(fmt))
-                Marshal.ThrowExceptionForHR(DV_E_FORMATETC);
+                return DV_E_FORMATETC;
 
-            medium = default(STGMEDIUM);
+            * medium = default(Interop.STGMEDIUM);
-            medium.tymed = TYMED.TYMED_HGLOBAL;
+            medium->tymed = TYMED.TYMED_HGLOBAL;
-            int result = WriteDataToHGlobal(fmt, ref medium.unionmember);
+            return WriteDataToHGlobal(fmt, ref medium->unionmember);
-            Marshal.ThrowExceptionForHR(result);
         }
 
-        void IOleDataObject.GetDataHere(ref FORMATETC format, ref STGMEDIUM medium)
+        unsafe uint Win32Com.IDataObject.GetDataHere(FORMATETC* format, Interop.STGMEDIUM* medium)
         {
-            if (_wrapped is IOleDataObject ole)
+            if (_wrapped is Win32Com.IDataObject ole)
             {
-                ole.GetDataHere(ref format, ref medium);
+                return ole.GetDataHere(format, medium);
-                return;
             }
 
-            if (medium.tymed != TYMED.TYMED_HGLOBAL || !format.tymed.HasAllFlags(TYMED.TYMED_HGLOBAL))
+            if (medium->tymed != TYMED.TYMED_HGLOBAL || !format->tymed.HasAllFlags(TYMED.TYMED_HGLOBAL))
-                Marshal.ThrowExceptionForHR(DV_E_TYMED);
+                return DV_E_TYMED;
 
-            if (format.dwAspect != DVASPECT.DVASPECT_CONTENT)
+            if (format->dwAspect != DVASPECT.DVASPECT_CONTENT)
-                Marshal.ThrowExceptionForHR(DV_E_DVASPECT);
+                return DV_E_DVASPECT;
 
-            string fmt = ClipboardFormats.GetFormat(format.cfFormat);
+            string fmt = ClipboardFormats.GetFormat(format->cfFormat);
             if (string.IsNullOrEmpty(fmt) || !_wrapped.Contains(fmt))
-                Marshal.ThrowExceptionForHR(DV_E_FORMATETC);
+                return DV_E_FORMATETC;
 
-            if (medium.unionmember == IntPtr.Zero)
+            if (medium->unionmember == IntPtr.Zero)
-                Marshal.ThrowExceptionForHR(STG_E_MEDIUMFULL);
+                return STG_E_MEDIUMFULL;
 
-            int result = WriteDataToHGlobal(fmt, ref medium.unionmember);
+            return WriteDataToHGlobal(fmt, ref medium->unionmember);
-            Marshal.ThrowExceptionForHR(result);
         }
 
-        int IOleDataObject.QueryGetData(ref FORMATETC format)
+        unsafe uint Win32Com.IDataObject.QueryGetData(FORMATETC* format)
         {
-            if (_wrapped is IOleDataObject ole)
+            if (_wrapped is Win32Com.IDataObject ole)
-                return ole.QueryGetData(ref format);
+            {
-            if (format.dwAspect != DVASPECT.DVASPECT_CONTENT)
+                return ole.QueryGetData(format);
+            }
+
+            if (format->dwAspect != DVASPECT.DVASPECT_CONTENT)
                 return DV_E_DVASPECT;
-            if (!format.tymed.HasAllFlags(TYMED.TYMED_HGLOBAL))
+            if (!format->tymed.HasAllFlags(TYMED.TYMED_HGLOBAL))
                 return DV_E_TYMED;
 
-            string dataFormat = ClipboardFormats.GetFormat(format.cfFormat);
+            var dataFormat = ClipboardFormats.GetFormat(format->cfFormat);
-            if (!string.IsNullOrEmpty(dataFormat) && _wrapped.Contains(dataFormat))
+
-                return unchecked((int)UnmanagedMethods.HRESULT.S_OK);
+            if (string.IsNullOrEmpty(dataFormat) || !_wrapped.Contains(dataFormat))
-            return DV_E_FORMATETC;
+                return DV_E_FORMATETC;
+
+            return 0;
         }
         
-        void IOleDataObject.SetData(ref FORMATETC formatIn, ref STGMEDIUM medium, bool release)
+        unsafe uint Win32Com.IDataObject.SetData(FORMATETC* pformatetc, Interop.STGMEDIUM* pmedium, int fRelease)
         {
-            if (_wrapped is IOleDataObject ole)
+            if (_wrapped is Win32Com.IDataObject ole)
             {
-                ole.SetData(ref formatIn, ref medium, release);
+                return ole.SetData(pformatetc, pmedium, fRelease);
-                return;
             }
-            Marshal.ThrowExceptionForHR(unchecked((int)UnmanagedMethods.HRESULT.E_NOTIMPL));
+            return (uint)UnmanagedMethods.HRESULT.E_NOTIMPL;
         }
 
-        private int WriteDataToHGlobal(string dataFormat, ref IntPtr hGlobal)
+        private uint WriteDataToHGlobal(string dataFormat, ref IntPtr hGlobal)
         {
             object data = _wrapped.Get(dataFormat);
             if (dataFormat == DataFormats.Text || data is string)
@@ -288,7 +302,7 @@ namespace Avalonia.Win32
             }
         }
 
-        private unsafe int WriteBytesToHGlobal(ref IntPtr hGlobal, ReadOnlySpan<byte> data)
+        private unsafe uint WriteBytesToHGlobal(ref IntPtr hGlobal, ReadOnlySpan<byte> data)
         {
             int required = data.Length;
             if (hGlobal == IntPtr.Zero)
@@ -312,7 +326,7 @@ namespace Avalonia.Win32
             }
         }
 
-        private int WriteFileListToHGlobal(ref IntPtr hGlobal, IEnumerable<string> files)
+        private uint WriteFileListToHGlobal(ref IntPtr hGlobal, IEnumerable<string> files)
         {
             if (!files?.Any() ?? false)
                 return unchecked((int)UnmanagedMethods.HRESULT.S_OK);
@@ -344,7 +358,7 @@ namespace Avalonia.Win32
             }
         }
 
-        private int WriteStringToHGlobal(ref IntPtr hGlobal, string data)
+        private uint WriteStringToHGlobal(ref IntPtr hGlobal, string data)
         {
             int required = (data.Length + 1) * sizeof(char);
             if (hGlobal == IntPtr.Zero)
@@ -367,6 +381,15 @@ namespace Avalonia.Win32
             }
         }
 
+        protected override void Destroyed()
+        {
+            ReleaseWrapped();
+        }
+
+        public void ReleaseWrapped()
+        {
+            _wrapped = null;
+        }
         #endregion
     }
 }

src/Windows/Avalonia.Win32/DragSource.cs

@@ -8,17 +8,26 @@ namespace Avalonia.Win32
 {
     class DragSource : IPlatformDragSource
     {
-        public Task<DragDropEffects> DoDragDrop(PointerEventArgs triggerEvent,
+        public unsafe Task<DragDropEffects> DoDragDrop(PointerEventArgs triggerEvent,
             IDataObject data, DragDropEffects allowedEffects)
         {
             Dispatcher.UIThread.VerifyAccess();
+
             triggerEvent.Pointer.Capture(null);
-            OleDragSource src = new OleDragSource();
+            
-            DataObject dataObject = new DataObject(data);
+            using var dataObject = new DataObject(data);
-            int allowed = (int)OleDropTarget.ConvertDropEffect(allowedEffects);
+            using var src = new OleDragSource();
+            var allowed = OleDropTarget.ConvertDropEffect(allowedEffects);
+            
+            var objPtr = MicroCom.MicroComRuntime.GetNativeIntPtr<Win32Com.IDataObject>(dataObject);
+            var srcPtr = MicroCom.MicroComRuntime.GetNativeIntPtr<Win32Com.IDropSource>(src);
+
+            UnmanagedMethods.DoDragDrop(objPtr, srcPtr, (int)allowed, out var finalEffect);
+            
+            // Force releasing of internal wrapper to avoid memory leak, if drop target keeps com reference.
+            dataObject.ReleaseWrapped();
 
-            UnmanagedMethods.DoDragDrop(dataObject, src, allowed, out var finalEffect);
+            return Task.FromResult(OleDropTarget.ConvertDropEffect((Win32Com.DropEffect)finalEffect));
-            return Task.FromResult(OleDropTarget.ConvertDropEffect((DropEffect)finalEffect));
         }
     }
 }

src/Windows/Avalonia.Win32/Interop/UnmanagedMethods.cs

@@ -1277,10 +1277,10 @@ namespace Avalonia.Win32.Interop
         public static extern IntPtr SetClipboardData(ClipboardFormat uFormat, IntPtr hMem);
 
         [DllImport("ole32.dll", PreserveSig = false)]
-        public static extern int OleGetClipboard(out IOleDataObject dataObject);
+        public static extern int OleGetClipboard(out IntPtr dataObject);
 
         [DllImport("ole32.dll", PreserveSig = true)]
-        public static extern int OleSetClipboard(IOleDataObject dataObject);
+        public static extern int OleSetClipboard(IntPtr dataObject);
 
         [DllImport("kernel32.dll", ExactSpelling = true)]
         public static extern IntPtr GlobalLock(IntPtr handle);
@@ -1424,7 +1424,7 @@ namespace Avalonia.Win32.Interop
         public static extern IntPtr CopyMemory(IntPtr dest, IntPtr src, UIntPtr count); 
         
         [DllImport("ole32.dll", CharSet = CharSet.Auto, ExactSpelling = true)]
-        public static extern HRESULT RegisterDragDrop(IntPtr hwnd, IDropTarget target);
+        public static extern HRESULT RegisterDragDrop(IntPtr hwnd, IntPtr target);
 
         [DllImport("ole32.dll", CharSet = CharSet.Auto, ExactSpelling = true)]
         public static extern HRESULT RevokeDragDrop(IntPtr hwnd);
@@ -1448,7 +1448,7 @@ namespace Avalonia.Win32.Interop
         public static extern int DragQueryFile(IntPtr hDrop, int iFile, StringBuilder lpszFile, int cch);
 
         [DllImport("ole32.dll", CharSet = CharSet.Auto, ExactSpelling = true, PreserveSig = false)]
-        internal static extern void DoDragDrop(IOleDataObject dataObject, IDropSource dropSource, int allowedEffects, out int finalEffect);
+        internal static extern void DoDragDrop(IntPtr dataObject, IntPtr dropSource, int allowedEffects, [Out] out int finalEffect);
 
         [DllImport("dwmapi.dll")]
         public static extern int DwmExtendFrameIntoClientArea(IntPtr hwnd, ref MARGINS margins);
@@ -2064,64 +2064,6 @@ namespace Avalonia.Win32.Interop
         }
     }
 
-    [Flags]
-    internal enum DropEffect : int
-    {
-        None = 0,
-        Copy = 1,
-        Move = 2,
-        Link = 4,
-        Scroll = -2147483648,
-    }
-
-    [ComImport]
-    [InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]
-    [Guid("00000122-0000-0000-C000-000000000046")]
-    internal interface IDropTarget
-    {
-        [PreserveSig]
-        UnmanagedMethods.HRESULT DragEnter([MarshalAs(UnmanagedType.Interface)] [In] IOleDataObject pDataObj, [MarshalAs(UnmanagedType.U4)] [In] int grfKeyState, [MarshalAs(UnmanagedType.U8)] [In] long pt, [In] [Out] ref DropEffect pdwEffect);
-        [PreserveSig]
-        UnmanagedMethods.HRESULT DragOver([MarshalAs(UnmanagedType.U4)] [In] int grfKeyState, [MarshalAs(UnmanagedType.U8)] [In] long pt, [In] [Out] ref DropEffect pdwEffect);
-        [PreserveSig]
-        UnmanagedMethods.HRESULT DragLeave();
-        [PreserveSig]
-        UnmanagedMethods.HRESULT Drop([MarshalAs(UnmanagedType.Interface)] [In] IOleDataObject pDataObj, [MarshalAs(UnmanagedType.U4)] [In] int grfKeyState, [MarshalAs(UnmanagedType.U8)] [In] long pt, [In] [Out] ref DropEffect pdwEffect);
-    }
-
-    [ComImport]
-    [InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]
-    [Guid("00000121-0000-0000-C000-000000000046")]
-    internal interface IDropSource
-    {
-        [PreserveSig]
-        int QueryContinueDrag(int fEscapePressed, [MarshalAs(UnmanagedType.U4)] [In] int grfKeyState);
-        [PreserveSig]
-        int GiveFeedback([MarshalAs(UnmanagedType.U4)] [In] int dwEffect);
-    }
-
-
-    [ComImport]
-    [Guid("0000010E-0000-0000-C000-000000000046")]
-    [InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]
-    internal interface IOleDataObject
-    {
-        void GetData([In] ref FORMATETC format, out STGMEDIUM medium);
-        void GetDataHere([In] ref FORMATETC format, ref STGMEDIUM medium);
-        [PreserveSig]
-        int QueryGetData([In] ref FORMATETC format);
-        [PreserveSig]
-        int GetCanonicalFormatEtc([In] ref FORMATETC formatIn, out FORMATETC formatOut);
-        void SetData([In] ref FORMATETC formatIn, [In] ref STGMEDIUM medium, [MarshalAs(UnmanagedType.Bool)] bool release);
-        IEnumFORMATETC EnumFormatEtc(DATADIR direction);
-        [PreserveSig]
-        int DAdvise([In] ref FORMATETC pFormatetc, ADVF advf, IAdviseSink adviseSink, out int connection);
-        void DUnadvise(int connection);
-        [PreserveSig]
-        int EnumDAdvise(out IEnumSTATDATA enumAdvise);
-    }
-
-
     [StructLayoutAttribute(LayoutKind.Sequential)]
     internal struct _DROPFILES
     {
@@ -2132,6 +2074,24 @@ namespace Avalonia.Win32.Interop
         public bool fWide;
     }
 
+    [StructLayoutAttribute(LayoutKind.Sequential)]
+    internal struct STGMEDIUM
+    {
+        public TYMED tymed;
+        public IntPtr unionmember;
+        public IntPtr pUnkForRelease;
+    }
+
+    [StructLayoutAttribute(LayoutKind.Sequential)]
+    internal struct FORMATETC
+    {
+        public ushort cfFormat;
+        public IntPtr ptd;
+        public DVASPECT dwAspect;
+        public int lindex;
+        public TYMED tymed;
+    }
+
     [Flags]
     internal enum PixelFormatDescriptorFlags : uint
     {

src/Windows/Avalonia.Win32/OleContext.cs

@@ -4,6 +4,7 @@ using System.Threading;
 using Avalonia.Platform;
 using Avalonia.Threading;
 using Avalonia.Win32.Interop;
+using Avalonia.Win32.Win32Com;
 
 namespace Avalonia.Win32
 {
@@ -46,7 +47,8 @@ namespace Avalonia.Win32
                 return false;
             }
 
-            return UnmanagedMethods.RegisterDragDrop(hwnd.Handle, target) == UnmanagedMethods.HRESULT.S_OK;
+            var trgPtr = MicroCom.MicroComRuntime.GetNativeIntPtr(target);
+            return UnmanagedMethods.RegisterDragDrop(hwnd.Handle, trgPtr) == UnmanagedMethods.HRESULT.S_OK;
         }
 
         internal bool UnregisterDragDrop(IPlatformHandle hwnd)

src/Windows/Avalonia.Win32/OleDataObject.cs

@@ -1,7 +1,6 @@
 using System;
 using System.Buffers;
 using System.Collections.Generic;
-using System.Diagnostics;
 using System.IO;
 using System.Linq;
 using System.Runtime.InteropServices;
@@ -9,17 +8,20 @@ using System.Runtime.InteropServices.ComTypes;
 using System.Runtime.Serialization.Formatters.Binary;
 using System.Text;
 using Avalonia.Input;
+using Avalonia.MicroCom;
 using Avalonia.Win32.Interop;
 
+using IDataObject = Avalonia.Input.IDataObject;
+
 namespace Avalonia.Win32
 {
-    class OleDataObject : Avalonia.Input.IDataObject
+    internal class OleDataObject : IDataObject, IDisposable
     {
-        private IOleDataObject _wrapped;
+        private readonly Win32Com.IDataObject _wrapped;
 
-        public OleDataObject(IOleDataObject wrapped)
+        public OleDataObject(Win32Com.IDataObject wrapped)
         {
-            _wrapped = wrapped;
+            _wrapped = wrapped.CloneReference();
         }
 
         public bool Contains(string dataFormat)
@@ -34,12 +36,12 @@ namespace Avalonia.Win32
 
         public string GetText()
         {
-            return GetDataFromOleHGLOBAL(DataFormats.Text, DVASPECT.DVASPECT_CONTENT) as string;
+            return (string)GetDataFromOleHGLOBAL(DataFormats.Text, DVASPECT.DVASPECT_CONTENT);
         }
 
         public IEnumerable<string> GetFileNames()
         {
-            return GetDataFromOleHGLOBAL(DataFormats.FileNames, DVASPECT.DVASPECT_CONTENT) as IEnumerable<string>;
+            return (IEnumerable<string>)GetDataFromOleHGLOBAL(DataFormats.FileNames, DVASPECT.DVASPECT_CONTENT);
         }
 
         public object Get(string dataFormat)
@@ -47,16 +49,17 @@ namespace Avalonia.Win32
             return GetDataFromOleHGLOBAL(dataFormat, DVASPECT.DVASPECT_CONTENT);
         }
 
-        private object GetDataFromOleHGLOBAL(string format, DVASPECT aspect)
+        private unsafe object GetDataFromOleHGLOBAL(string format, DVASPECT aspect)
         {
-            FORMATETC formatEtc = new FORMATETC();
+            var formatEtc = new Interop.FORMATETC();
             formatEtc.cfFormat = ClipboardFormats.GetFormat(format);
             formatEtc.dwAspect = aspect;
             formatEtc.lindex = -1;
             formatEtc.tymed = TYMED.TYMED_HGLOBAL;
-            if (_wrapped.QueryGetData(ref formatEtc) == 0)
+            if (_wrapped.QueryGetData(&formatEtc) == 0)
             {
-                _wrapped.GetData(ref formatEtc, out STGMEDIUM medium);
+                Interop.STGMEDIUM medium = default;
+                _ = _wrapped.GetData(&formatEtc, &medium);
                 try
                 {
                     if (medium.unionmember != IntPtr.Zero && medium.tymed == TYMED.TYMED_HGLOBAL)
@@ -140,38 +143,53 @@ namespace Avalonia.Win32
             }
         }
 
-        private IEnumerable<string> GetDataFormatsCore()
+        private unsafe IEnumerable<string> GetDataFormatsCore()
         {
-            var enumFormat = _wrapped.EnumFormatEtc(DATADIR.DATADIR_GET);
+            var formatsList = new List<string>();
+            var enumFormat = _wrapped.EnumFormatEtc((int)DATADIR.DATADIR_GET);
 
             if (enumFormat != null)
             {
                 enumFormat.Reset();
                 
-                var formats = ArrayPool<FORMATETC>.Shared.Rent(1);
+                var formats = ArrayPool<Interop.FORMATETC>.Shared.Rent(1);
-                var fetched = ArrayPool<int>.Shared.Rent(1);
 
                 try
                 {
+                    uint fetched = 0;
                     do
                     {
-                        fetched[0] = 0;
+                        fixed (Interop.FORMATETC* formatsPtr = formats)
-                        if (enumFormat.Next(1, formats, fetched) == 0 && fetched[0] > 0)
+                        {
+                            // Read one item at a time.
+                            // When "celt" parameter is 1, "pceltFetched" is ignored.
+                            var res = enumFormat.Next(1, formatsPtr, &fetched);
+                            if (res != 0)
+                            {
+                                break;
+                            }
+                        }
+                        if (fetched > 0)
                         {
                             if (formats[0].ptd != IntPtr.Zero)
                                 Marshal.FreeCoTaskMem(formats[0].ptd);
 
-                            yield return ClipboardFormats.GetFormat(formats[0].cfFormat);
+                            formatsList.Add(ClipboardFormats.GetFormat(formats[0].cfFormat));
                         }
                     }
-                    while (fetched[0] > 0);
+                    while (fetched > 0);
                 }
                 finally
                 {
-                    ArrayPool<FORMATETC>.Shared.Return(formats);
+                    ArrayPool<Interop.FORMATETC>.Shared.Return(formats);
-                    ArrayPool<int>.Shared.Return(fetched);
                 }
             }
+            return formatsList;
+        }
+
+        public void Dispose()
+        {
+            _wrapped.Dispose();
         }
     }
 }

src/Windows/Avalonia.Win32/OleDragSource.cs

@@ -1,9 +1,12 @@
 using System.Linq;
+
+using Avalonia.MicroCom;
 using Avalonia.Win32.Interop;
+using Avalonia.Win32.Win32Com;
 
 namespace Avalonia.Win32
 {
-    class OleDragSource : IDropSource
+    internal class OleDragSource : CallbackBase, IDropSource
     {
         private const int DRAGDROP_S_USEDEFAULTCURSORS = 0x00040102;
         private const int DRAGDROP_S_DROP = 0x00040100;
@@ -30,7 +33,7 @@ namespace Avalonia.Win32
             return unchecked((int)UnmanagedMethods.HRESULT.S_OK);
         }
 
-        public int GiveFeedback(int dwEffect)
+        public int GiveFeedback(DropEffect dwEffect)
         {
             return DRAGDROP_S_USEDEFAULTCURSORS;
         }

src/Windows/Avalonia.Win32/OleDropTarget.cs

@@ -1,12 +1,15 @@
-using Avalonia.Input;
+using System;
+
+using Avalonia.Input;
 using Avalonia.Input.Raw;
+using Avalonia.MicroCom;
 using Avalonia.Platform;
 using Avalonia.Win32.Interop;
-using IDataObject = Avalonia.Input.IDataObject;
+using DropEffect = Avalonia.Win32.Win32Com.DropEffect;
 
 namespace Avalonia.Win32
 {
-    internal class OleDropTarget : IDropTarget
+    internal class OleDropTarget : CallbackBase, Win32Com.IDropTarget
     {
         private readonly IInputRoot _target;
         private readonly ITopLevelImpl _tl;
@@ -65,58 +68,51 @@ namespace Avalonia.Win32
             return modifiers;
         }
 
-        UnmanagedMethods.HRESULT IDropTarget.DragEnter(IOleDataObject pDataObj, int grfKeyState, long pt, ref DropEffect pdwEffect)
+        unsafe void Win32Com.IDropTarget.DragEnter(Win32Com.IDataObject pDataObj, int grfKeyState, UnmanagedMethods.POINT pt, DropEffect* pdwEffect)
         {
             var dispatch = _tl?.Input;
             if (dispatch == null)
             {
-                pdwEffect = DropEffect.None;
+                *pdwEffect= (int)DropEffect.None;
-                return UnmanagedMethods.HRESULT.S_OK;
             }
-            _currentDrag = pDataObj as IDataObject;
+
-            if (_currentDrag == null)
+            SetDataObject(pDataObj);
-                _currentDrag = new OleDataObject(pDataObj);
 
             var args = new RawDragEvent(
                 _dragDevice,
                 RawDragEventType.DragEnter, 
-                _target, 
+                _target,
-                GetDragLocation(pt), 
+                GetDragLocation(pt),
                 _currentDrag, 
-                ConvertDropEffect(pdwEffect),
+                ConvertDropEffect(*pdwEffect),
                 ConvertKeyState(grfKeyState)
             );
             dispatch(args);
-            pdwEffect = ConvertDropEffect(args.Effects);
+            *pdwEffect = ConvertDropEffect(args.Effects);
-            
-            return UnmanagedMethods.HRESULT.S_OK;
         }
 
-        UnmanagedMethods.HRESULT IDropTarget.DragOver(int grfKeyState, long pt, ref DropEffect pdwEffect)
+        unsafe void Win32Com.IDropTarget.DragOver(int grfKeyState, UnmanagedMethods.POINT pt, DropEffect* pdwEffect)
         {
             var dispatch = _tl?.Input;
             if (dispatch == null)
             {
-                pdwEffect = DropEffect.None;
+                *pdwEffect = (int)DropEffect.None;
-                return UnmanagedMethods.HRESULT.S_OK;
             }
             
             var args = new RawDragEvent(
                 _dragDevice,
                 RawDragEventType.DragOver, 
-                _target, 
+                _target,
-                GetDragLocation(pt), 
+                GetDragLocation(pt),
-                _currentDrag, 
+                _currentDrag,
-                ConvertDropEffect(pdwEffect),
+                ConvertDropEffect(*pdwEffect),
                 ConvertKeyState(grfKeyState)
             );
             dispatch(args);
-            pdwEffect = ConvertDropEffect(args.Effects);
+            *pdwEffect = ConvertDropEffect(args.Effects);
-            
-            return UnmanagedMethods.HRESULT.S_OK;  
         }
 
-        UnmanagedMethods.HRESULT IDropTarget.DragLeave()
+        void Win32Com.IDropTarget.DragLeave()
         {
             try
             {
@@ -129,56 +125,91 @@ namespace Avalonia.Win32
                     DragDropEffects.None,
                     RawInputModifiers.None
                 ));
-                return UnmanagedMethods.HRESULT.S_OK;
             }
             finally
             {
-                _currentDrag = null;
+                ReleaseDataObject();
             }
         }
 
-        UnmanagedMethods.HRESULT IDropTarget.Drop(IOleDataObject pDataObj, int grfKeyState, long pt, ref DropEffect pdwEffect)
+        unsafe void Win32Com.IDropTarget.Drop(Win32Com.IDataObject pDataObj, int grfKeyState, UnmanagedMethods.POINT pt, DropEffect* pdwEffect)
         {
             try
             {
                 var dispatch = _tl?.Input;
                 if (dispatch == null)
                 {
-                    pdwEffect = DropEffect.None;
+                    *pdwEffect = (int)DropEffect.None;
-                    return UnmanagedMethods.HRESULT.S_OK;
                 }
 
-                _currentDrag = pDataObj as IDataObject;
+                SetDataObject(pDataObj);
-                if (_currentDrag == null)
+
-                    _currentDrag= new OleDataObject(pDataObj);
-                
                 var args = new RawDragEvent(
                     _dragDevice, 
                     RawDragEventType.Drop, 
-                    _target, 
+                    _target,
-                    GetDragLocation(pt), 
+                    GetDragLocation(pt),
-                    _currentDrag, 
+                    _currentDrag,
-                    ConvertDropEffect(pdwEffect),
+                    ConvertDropEffect(*pdwEffect),
                     ConvertKeyState(grfKeyState)
                 );
                 dispatch(args);
-                pdwEffect = ConvertDropEffect(args.Effects);
+                *pdwEffect = ConvertDropEffect(args.Effects);
-            
-                return UnmanagedMethods.HRESULT.S_OK;  
             }
             finally
             {
-                _currentDrag = null;
+                ReleaseDataObject();
             }
         }
 
-        private Point GetDragLocation(long dragPoint)
+        private void SetDataObject(Win32Com.IDataObject pDataObj)
         {
-            int x = (int)dragPoint;
+            var newDrag = GetAvaloniaObjectFromCOM(pDataObj);
-            int y = (int)(dragPoint >> 32);
+            if (_currentDrag != newDrag)
+            {
+                ReleaseDataObject();
+                _currentDrag = newDrag;
+            }
+        }
 
-            var screenPt = new PixelPoint(x, y);
+        private void ReleaseDataObject()
+        {
+            // OleDataObject keeps COM reference, so it should be disposed.
+            if (_currentDrag is OleDataObject oleDragSource)
+            {
+                oleDragSource?.Dispose();
+                _currentDrag = null;
+            }
+        }
+
+        private Point GetDragLocation(UnmanagedMethods.POINT dragPoint)
+        {
+            var screenPt = new PixelPoint(dragPoint.X, dragPoint.Y);
             return _target.PointToClient(screenPt);
         }
+
+        protected override void Destroyed()
+        {
+            ReleaseDataObject();
+        }
+
+        public static unsafe IDataObject GetAvaloniaObjectFromCOM(Win32Com.IDataObject pDataObj)
+        {
+            if (pDataObj is null)
+            {
+                throw new ArgumentNullException(nameof(pDataObj));
+            }
+            if (pDataObj is IDataObject disposableDataObject)
+            {
+                return disposableDataObject;
+            }
+
+            var dataObject = MicroComRuntime.TryUnwrapManagedObject(pDataObj) as DataObject;
+            if (dataObject is not null)
+            {
+                return dataObject;
+            }
+            return new OleDataObject(pDataObj);
+        }
     }
 }

src/Windows/Avalonia.Win32/Win32Com/win32.idl

@@ -27,6 +27,8 @@
 @clr-map REFGUID System.Guid*
 @clr-map REFIID System.Guid*
 @clr-map WCHAR System.Char
+@clr-map STGMEDIUM Avalonia.Win32.Interop.STGMEDIUM
+@clr-map FORMATETC Avalonia.Win32.Interop.FORMATETC
 
 [flags]
 enum FILEOPENDIALOGOPTIONS
@@ -53,6 +55,16 @@ enum FILEOPENDIALOGOPTIONS
     FOS_DEFAULTNOMINIMODE = 0x20000000
 }
 
+[flags]
+enum DropEffect
+{
+    None = 0,
+    Copy = 1,
+    Move = 2,
+    Link = 4,
+    Scroll = -2147483648,
+}
+
 [
     object,
     uuid(43826d1e-e718-42ee-bc55-a1e261c37bfe),
@@ -189,3 +201,114 @@ interface IFileOpenDialog : IFileDialog
     HRESULT GetSelectedItems(
         [out] IShellItemArray** ppsai);
 }
+
+[
+    object,
+    uuid(00000103-0000-0000-C000-000000000046),
+    pointer_default(unique)
+]
+interface IEnumFORMATETC : IUnknown
+{
+    UINT32 Next(
+        [in] ULONG celt,
+        [out] FORMATETC* rgelt,
+        ULONG* pceltFetched);
+
+    UINT32 Skip(
+        [in] ULONG celt);
+
+    HRESULT Reset();
+
+    HRESULT Clone(
+        [out] IEnumFORMATETC** ppenum);
+}
+
+[
+    object,
+    uuid(0000010e-0000-0000-C000-000000000046),
+    pointer_default(unique)
+]
+interface IDataObject : IUnknown
+{
+    UINT32 GetData(
+        [in, unique] FORMATETC* pformatetcIn,
+        [out] STGMEDIUM* pmedium);
+
+    UINT32 GetDataHere(
+        [in, unique] FORMATETC* pformatetc,
+        [in] STGMEDIUM* pmedium);
+
+    UINT32 QueryGetData(
+        [in, unique] FORMATETC* pformatetc);
+
+    HRESULT GetCanonicalFormatEtc(
+        [in, unique] FORMATETC* pformatectIn,
+        [out] FORMATETC* pformatetcOut);
+
+    UINT32 SetData(
+        [in, unique] FORMATETC* pformatetc,
+        [in, unique] STGMEDIUM* pmedium,
+        [in] BOOL fRelease);
+
+    HRESULT EnumFormatEtc(
+        [in] DWORD dwDirection,
+        [out] IEnumFORMATETC** ppenumFormatEtc);
+
+    HRESULT DAdvise(
+        [in] FORMATETC* pformatetc,
+        [in] DWORD advf,
+        [in, unique] void* pAdvSink,
+        [out] DWORD* pdwConnection);
+
+    HRESULT DUnadvise(
+        [in] DWORD dwConnection);
+
+    HRESULT EnumDAdvise(
+        [out] void** ppenumAdvise);
+}
+
+[
+    local,
+    object,
+    uuid(00000121-0000-0000-C000-000000000046)
+]
+
+interface IDropSource : IUnknown
+{
+    INT32 QueryContinueDrag([in] BOOL fEscapePressed, [in] DWORD grfKeyState);
+
+    INT32 GiveFeedback([in] DropEffect dwEffect);
+}
+
+[
+    object,
+    uuid(00000122-0000-0000-C000-000000000046),
+    pointer_default(unique)
+]
+interface IDropTarget : IUnknown
+{
+    HRESULT DragEnter
+    (
+        [in, unique] IDataObject* pDataObj,
+        [in] DWORD grfKeyState,
+        [in] POINT pt,
+        [in] DropEffect* pdwEffect
+    );
+
+    HRESULT DragOver
+    (
+        [in] DWORD grfKeyState,
+        [in] POINT pt,
+        [in] DropEffect* pdwEffect
+    );
+
+    HRESULT DragLeave();
+
+    HRESULT Drop
+    (
+        [in, unique] IDataObject* pDataObj,
+        [in] DWORD grfKeyState,
+        [in] POINT pt,
+        [in] DropEffect* pdwEffect
+    );
+}

src/Windows/Avalonia.Win32/WindowImpl.cs

@@ -529,6 +529,7 @@ namespace Avalonia.Win32
             if (_dropTarget != null)
             {
                 OleContext.Current?.UnregisterDragDrop(Handle);
+                _dropTarget.Dispose();
                 _dropTarget = null;
             }
 

tests/Avalonia.Animation.UnitTests/BrushTransitionTests.cs

@@ -0,0 +1,54 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+using Avalonia.Controls;
+using Avalonia.Media;
+using Xunit;
+
+namespace Avalonia.Animation.UnitTests
+{
+    public class BrushTransitionTests
+    {
+        [Fact]
+        public void SolidColorBrush_Opacity_IsInteroplated()
+        {
+            Test(0, new SolidColorBrush { Opacity = 0 }, new SolidColorBrush { Opacity = 0 });
+            Test(0, new SolidColorBrush { Opacity = 0 }, new SolidColorBrush { Opacity = 1 });
+            Test(0.5, new SolidColorBrush { Opacity = 0 }, new SolidColorBrush { Opacity = 1 });
+            Test(0.5, new SolidColorBrush { Opacity = 0.5 }, new SolidColorBrush { Opacity = 0.5 });
+            Test(1, new SolidColorBrush { Opacity = 1 }, new SolidColorBrush { Opacity = 1 });
+            // TODO: investigate why this case fails.
+            //Test2(1, new SolidColorBrush { Opacity = 0 }, new SolidColorBrush { Opacity = 1 });
+        }
+
+        [Fact]
+        public void LinearGradientBrush_Opacity_IsInteroplated()
+        {
+            Test(0, new LinearGradientBrush { Opacity = 0 }, new LinearGradientBrush { Opacity = 0 });
+            Test(0, new LinearGradientBrush { Opacity = 0 }, new LinearGradientBrush { Opacity = 1 });
+            Test(0.5, new LinearGradientBrush { Opacity = 0 }, new LinearGradientBrush { Opacity = 1 });
+            Test(0.5, new LinearGradientBrush { Opacity = 0.5 }, new LinearGradientBrush { Opacity = 0.5 });
+            Test(1, new LinearGradientBrush { Opacity = 1 }, new LinearGradientBrush { Opacity = 1 });
+        }
+
+        private static void Test(double progress, IBrush oldBrush, IBrush newBrush)
+        {
+            var clock = new TestClock();
+            var border = new Border() { Background = oldBrush };
+            BrushTransition sut = new BrushTransition
+            {
+                Duration = TimeSpan.FromSeconds(1),
+                Property = Border.BackgroundProperty
+            };
+
+            sut.Apply(border, clock, oldBrush, newBrush);
+            clock.Pulse(TimeSpan.Zero);
+            clock.Pulse(sut.Duration * progress);
+
+            Assert.NotNull(border.Background);
+            Assert.Equal(oldBrush.Opacity + (newBrush.Opacity - oldBrush.Opacity) * progress, border.Background.Opacity);
+        }
+    }
+}