We currently have a Silverlight UI (which we are unable to change from at this stage) for our system, which has very limited drag drop capabilities. We are currently running out of browser with elevated trust. So in order to handle Silverlight's shortcomings I have created a c++ com library in order to handle Drag Drop events. This works perfectly well for incoming events from other applications, however I'm struggling to get the Drag operations, with our app as the source, working correctly. Most of the files to be dragged from the app will be virtual, which I have managed to get working however regardless of everything I've tried I have been unable to get the operation to be asynchronous, and the app locks up during the process.
I initially implemented only the IAsyncOperation (need backward compatibility to xp), which had no apparent affect. My DataObject is queried for the interface, gets the ref. A Call to GetAsyncMode is made, which returns VARIANT_TRUE, and a call to StartOperation is made. However all operations are done on the same thread (ui thread) and no async seems to be in affect.
I Subsequently tried implementing ICallFactory to return an AsyncIDataObject. Here explorer seems to check for the ICallFactory interface, calls the CreateCall on the call object and queries it to make sure it has the correct interfaces. Using the symbol servers I am able to see that it this occurs in the AsyncStubInvoke call stack. From here a call to StdStubBuffer_QueryInterface is made which is searching for the ICallFactory interface. This check fails and I unfortunately cannot see what object is being checked for this interface. After this fails the call seems to fall back to SyncStubInvoke after an operation not supported error (following from the Interface not supported error). All of this too seems to have no effect on the end result and the call is still apparently synchronous with the source app locking up.
My DragDrop class which exposes the com calls is CComMultiThreadModel. I have tried using my DataObject as a basic class not inheriting from CComObjectRootEx and a wrapper IDataObject class which is defined in the IDL as well and does inherit from CComObjectRootEx as is also CComMultiThreadModel. I have also tried having this class inherit from IDispatch as well as IUnknown.
Any feedback would be greatly appreciated.