Fix memory leak DoDragDrop never releasing object

samples/ControlCatalog/Pages/ClipboardPage.xaml.cs

@@ -36,26 +36,31 @@ namespace ControlCatalog.Pages
         private async void CopyTextDataObject(object sender, RoutedEventArgs args)
         {
             var dataObject = new DataObject();
-            dataObject.Set(DataFormats.Text, ClipboardContent.Text);
+            dataObject.Set(DataFormats.Text, ClipboardContent.Text ?? string.Empty);
             await Application.Current.Clipboard.SetDataObjectAsync(dataObject);
         }
 
         private async void PasteTextDataObject(object sender, RoutedEventArgs args)
         {
-            ClipboardContent.Text = (string)await Application.Current.Clipboard.GetDataAsync(DataFormats.Text);
+            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, ClipboardContent.Text.Split(new[] { Environment.NewLine }, StringSplitOptions.RemoveEmptyEntries));
+            dataObject.Set(DataFormats.FileNames, files);
             await Application.Current.Clipboard.SetDataObjectAsync(dataObject);
         }
 
         private async void PasteFilesDataObject(object sender, RoutedEventArgs args)
         {
-            var fiels = (IEnumerable<string>)await Application.Current.Clipboard.GetDataAsync(DataFormats.FileNames);
-            ClipboardContent.Text = string.Join(Environment.NewLine, fiels);
+            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)

src/Windows/Avalonia.Win32/DataObject.cs

@@ -16,31 +16,7 @@ using IDataObject = Avalonia.Input.IDataObject;
 
 namespace Avalonia.Win32
 {
-    public interface IDisposableDataObject : IDataObject, IDisposable { }
-
-    internal static class DataObjectEx
-    {
-        public static unsafe IDisposableDataObject GetAvaloniaObjectFromCOM(this Win32Com.IDataObject pDataObj)
-        {
-            if (pDataObj is null)
-            {
-                throw new ArgumentNullException(nameof(pDataObj));
-            }
-            if (pDataObj is IDisposableDataObject disposableDataObject)
-            {
-                return disposableDataObject;
-            }
-
-            var dataObject = MicroComRuntime.TryUnwrapManagedObject(pDataObj) as DataObject;
-            if (dataObject is not null)
-            {
-                return dataObject;
-            }
-            return new OleDataObject(pDataObj);
-        }
-    }
-
-    internal class DataObject : CallbackBase, IDisposableDataObject, Win32Com.IDataObject
+    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();
@@ -124,10 +100,14 @@ namespace Avalonia.Win32
         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();
@@ -403,7 +383,12 @@ namespace Avalonia.Win32
 
         protected override void Destroyed()
         {
-            base.Destroyed();
+            ReleaseWrapped();
+        }
+
+        public void ReleaseWrapped()
+        {
+            _wrapped = null;
         }
         #endregion
     }

src/Windows/Avalonia.Win32/DragSource.cs

@@ -23,6 +23,10 @@ namespace Avalonia.Win32
             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();
+
             return Task.FromResult(OleDropTarget.ConvertDropEffect((Win32Com.DropEffect)finalEffect));
         }
     }

src/Windows/Avalonia.Win32/OleDataObject.cs

@@ -11,9 +11,11 @@ using Avalonia.Input;
 using Avalonia.MicroCom;
 using Avalonia.Win32.Interop;
 
+using IDataObject = Avalonia.Input.IDataObject;
+
 namespace Avalonia.Win32
 {
-    internal class OleDataObject : IDisposableDataObject
+    internal class OleDataObject : IDataObject, IDisposable
     {
         private readonly Win32Com.IDataObject _wrapped;
 

src/Windows/Avalonia.Win32/OleDropTarget.cs

@@ -1,4 +1,6 @@
-using Avalonia.Input;
+using System;
+
+using Avalonia.Input;
 using Avalonia.Input.Raw;
 using Avalonia.MicroCom;
 using Avalonia.Platform;
@@ -13,7 +15,7 @@ namespace Avalonia.Win32
         private readonly ITopLevelImpl _tl;
         private readonly IDragDropDevice _dragDevice;
         
-        private IDisposableDataObject _currentDrag = null;
+        private IDataObject _currentDrag = null;
 
         public OleDropTarget(ITopLevelImpl tl, IInputRoot target)
         {
@@ -74,12 +76,7 @@ namespace Avalonia.Win32
                 *pdwEffect= (int)DropEffect.None;
             }
 
-            var newDrag = pDataObj.GetAvaloniaObjectFromCOM();
-            if (_currentDrag != newDrag)
-            {
-                _currentDrag?.Dispose();
-                _currentDrag = newDrag;
-            }
+            SetDataObject(pDataObj);
 
             var args = new RawDragEvent(
                 _dragDevice,
@@ -131,8 +128,7 @@ namespace Avalonia.Win32
             }
             finally
             {
-                _currentDrag?.Dispose();
-                _currentDrag = null;
+                ReleaseDataObject();
             }
         }
 
@@ -146,12 +142,7 @@ namespace Avalonia.Win32
                     *pdwEffect = (int)DropEffect.None;
                 }
 
-                var newDrag = pDataObj.GetAvaloniaObjectFromCOM();
-                if (_currentDrag != newDrag)
-                {
-                    _currentDrag?.Dispose();
-                    _currentDrag = newDrag;
-                }
+                SetDataObject(pDataObj);
 
                 var args = new RawDragEvent(
                     _dragDevice, 
@@ -167,7 +158,26 @@ namespace Avalonia.Win32
             }
             finally
             {
-                _currentDrag?.Dispose();
+                ReleaseDataObject();
+            }
+        }
+
+        private void SetDataObject(Win32Com.IDataObject pDataObj)
+        {
+            var newDrag = GetAvaloniaObjectFromCOM(pDataObj);
+            if (_currentDrag != newDrag)
+            {
+                ReleaseDataObject();
+                _currentDrag = newDrag;
+            }
+        }
+
+        private void ReleaseDataObject()
+        {
+            // OleDataObject keeps COM reference, so it should be disposed.
+            if (_currentDrag is OleDataObject oleDragSource)
+            {
+                oleDragSource?.Dispose();
                 _currentDrag = null;
             }
         }
@@ -180,7 +190,26 @@ namespace Avalonia.Win32
 
         protected override void Destroyed()
         {
-            _currentDrag?.Dispose();
+            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);
         }
     }
 }