Question

I’m trying to convert System::Windows::Forms::IDataObject into the native IDataObject defined in the ObjIdl.h. Unfortunately the following source code doesn’t return the native IDataObject.

IntPtr pData = System::Runtime::InteropServices::Marshal::GetIUnknownForObject(e->Data);
::IDataObject* data = (::IDataObject*) pData.ToPointer();

How can I get the native IDataObject in a Windows Forms application during Drag and Drop?

Answer 1

Casting a COM interface pointer with a C-style cast is not legal. You have to ask nicely with the QueryInterface() method. Like this:

 System::Windows::Forms::IDataObject^ obj = Clipboard::GetDataObject();
 ::IUnknown* punk = (::IUnknown*)System::Runtime::InteropServices::Marshal::GetIUnknownForObject(obj).ToPointer();
 ::IDataObject* pdata = nullptr;
 HRESULT hr = punk->QueryInterface(__uuidof(::IDataObject), (void**)&pdata);
 if (SUCCEEDED(hr)) {
     // etc..
 }