The Old New Thing

Why do I get E_NOINTERFACE when creating an object that supports that interface?

December 13, 2004 Dec 13, 2004 12/13/04

Raymond Chen

I've seen a few questions from people who call the CoCreateInstance function, asking for an interface that they know the object supports, yet receiving error E_NOINTERFACE. What's going on? You're seeing the same problem as the missing IMarshal, just from the other side. If your threading model is incompatible with the threading model ...

Dragging a shell object, part 5: Making somebody else do the heavy lifting

December 10, 2004 Dec 10, 2004 12/10/04

Raymond Chen

Creating that drag image was a bit of work. Fortunately, the listview control is willing to do some of the work for you. Throw away the OnLButtonDown function (and the HANDLE_MESSAGE that goes with it). Instead, we'll make the listview do all our presentation for us. BOOL OnCreate(HWND hwnd, LPCREATESTRUCT lpcs) { g_hwndChild = ...

Dragging a shell object, part 4: Adding a prettier drag icon

December 9, 2004 Dec 9, 2004 12/9/04

Raymond Chen

You may have noticed that the drag feedback is rather sad-looking. Just a box, maybe with a plus sign or an arrow; you don't even know what it is you're dragging. Let's fix that. We'll drag the icon of the file around. We'll need to add the drag image to the data object. void OnLButtonDown(HWND hwnd, BOOL fDoubleClick, int x, int y, UINT...

Dragging a shell object, part 3: Detecting an optimized move

December 8, 2004 Dec 8, 2004 12/8/04

Raymond Chen

We were considering how to detect that the drag/drop operation resulted in a conceptual Move even if the DROPEFFECT_MOVE was optimized away. If the drop target is the shell, you can query the data object for CFSTR_PERFORMEDDROPEFFECT to see what the performed effect was. void OnLButtonDown(HWND hwnd, BOOL fDoubleClick, ...

Dragging a shell object, part 2: Enabling the Move operation

December 7, 2004 Dec 7, 2004 12/7/04

Raymond Chen

Let's say that we did want to support Move in our drag/drop program, for whatever reason. Let's do it with some scratch file instead of clock.avi, though. Create a file somewhere that you don't mind losing; let's say it's C:\throwaway.txt. Change the function OnLButtonDown as follows: void OnLButtonDown(HWND hwnd, BOOL fDoubleClick...