not working on windows 11, 0x80040064 (DV_E_FORMATETC)

[MadTom-Zh]

when drag virtual file out, an exception throwed:

System.Runtime.InteropServices.COMException: 'Invalid FORMATETC structure (Exception from HRESULT: 0x80040064 (DV_E_FORMATETC))'

at System.Runtime.InteropServices.Marshal.ThrowExceptionForHRInternal(Int32 errorCode, IntPtr errorInfo)
at System.Runtime.InteropServices.Marshal.ThrowExceptionForHR(Int32 errorCode)
at DragVirtual.VirtualFileDataObject.System.Runtime.InteropServices.ComTypes.IDataObject.GetData(FORMATETC& format, STGMEDIUM& medium) in C:\tmp\VirtualDragDrop-master\VirtualFileDataObject.cs:line 219

[MadTom-Zh]

ok, for some reason, when run the exe without debugging, it just works, don't know why...

[dotriz]

This is a known and common issue with virtual drag-and-drop implementations in C#, especially when using a custom IDataObject implementation like the one in VirtualFileDataObject.

The key point:

✅ Why it works in Release but throws an exception in Debug

In Debug mode, Visual Studio enables COM exception debugging:

Debug → Options → Debugging → Enable Just-My-Code → On
Debug → Options → Debugging → Break on COM Exceptions → On by default

This causes the debugger to break on expected COM exceptions, even when the application handles them internally.
Drag-and-Drop via virtual files always triggers multiple FORMATETC queries from Explorer. Some of them intentionally fail.

So:

✔️ The exception is expected behavior

Explorer tries different FORMATETC combinations until one works.
Your implementation returns DV_E_FORMATETC for unsupported combinations (correct behavior), but Debugger stops on it.

✔️ In Release mode, the exception is swallowed normally

Because the exception is COM and is returned via HRESULT, not thrown as .NET exception.

🔧 Fix / Workaround (recommended)

Disable "Break on COM Exceptions"

In Visual Studio:

Go to Debug > Windows > Exception Settings

Search for COMException

Uncheck:

System.Runtime.InteropServices.COMException

or specifically turn off breaking on:

HRESULT: 0x80040064 (DV_E_FORMATETC)