DataGridRow Drag and Drop Visual does not display most of the time

[omnilogix]

Describe the bug

When performing a Drag and Drop operation with DataGridRow, about 80% of the time the Row visual will not display during dragging. It does not matter whether the visual is specifically set in code, or the default action.

Steps to reproduce the bug

Steps to reproduce the behavior:

1. Add a DataGrid with rows on a page:
2. Enable Drag and Drop for DataGridRows as necessary:
3. Peform drag operation and observe that the Visual of the row data is often omitted from the drag. Instead you may see the Caption and/or Glyph

private void OnLoadingRow(object sender, Microsoft.Toolkit.Uwp.UI.Controls.DataGridRowEventArgs e)
        {
            e.Row.CanDrag = true;
            e.Row.AllowDrop = true;
            e.Row.DragStarting += Row_DragStarting;
            e.Row.DropCompleted += Row_DropCompleted;
            e.Row.DragEnter += Row_DragEnter;
            e.Row.DragOver += Row_DragOver;
            e.Row.DragLeave += Row_DragLeave;
            e.Row.Drop += Row_Drop;
        }

Optionally, code the visual yourself

private async void Row_DragStarting(UIElement sender, DragStartingEventArgs args)
        {
            args.AllowedOperations = Windows.ApplicationModel.DataTransfer.DataPackageOperation.Move;

            if (sender is DataGridRow row)
            {
                var def = args.GetDeferral();
                var rtb = new RenderTargetBitmap() { };
                await rtb.RenderAsync(row);
                IBuffer pixelBuffer = await rtb.GetPixelsAsync();
                SoftwareBitmap b = SoftwareBitmap.CreateCopyFromBuffer(pixelBuffer, BitmapPixelFormat.Bgra8, (int)rtb.PixelWidth, (int)rtb.PixelHeight);

                args.DragUI.SetContentFromSoftwareBitmap(b, new Point(rtb.PixelWidth / 2, rtb.PixelHeight / 2));
                def.Complete();
            }
        }

Expected behavior
Automatic rendering of the Drag Visual for a DataGridRow

Screenshots

Version Info

NuGet package version:

Windows app type:

UWP	Win32
	YES

Windows 10 version	Saw the problem?
Insider Build (xxxxx)
October 2020 Update (19042)	YES
May 2020 Update (19041)
November 2019 Update (18363)
May 2019 Update (18362)
October 2018 Update (17763)
April 2018 Update (17134)
Fall Creators Update (16299)
Creators Update (15063)

Device form factor	Saw the problem?
Desktop	YES
Xbox
Surface Hub
IoT

Additional context

[jschwizer99]

I observe a similar behavior when starting the drag operation by StartDragAsync. In some cases, the correct behavior is triggered and the element gets moved around. But sometimes I just see the initial DataPackageOperation::None. The events DragStarting and DragOver are triggered correctly. Attaching modifications to DragUIOverride in the DragOver works fine. It is the attachment at drag start which fails. The frequency of the failure is system-dependent, which could point in direction of a race.

[codendone]

We just debugged this issue last week. This is unfortunately a bug in Windows specific to non-UWP apps. It isn't clear right now if we can fix this in WinUI3. On the plus side, this has been fixed in Windows, and is available in current Dev Channel builds from the Windows Insider Program.

[codendone]

Note: In theory it is possible to avoid the issue if you can avoid any awaits (and taking a deferral) in your DragStarting handler. But that likely isn't reasonable for most uses to already have the bitmap ready.

[codendone]

Since #4528 is the same issue, I'm going to close this issue. You can track that one for status.