RegisterDragDrop

Registers the specified window as a window that can be the target of an OLE drag and drop operation and specifies the IDropTarget instance to use for drop operations.

HRESULT RegisterDragDrop(

HWND hwnd,	//Window that can accept drops
IDropTarget * pDropTarget	//Points to the IDropTarget interface
);

Parameters
hwnd
Specifies the handle to a window that can be a target for an OLE drag and drop operation.
pDropTarget
Specifies the IDropTarget instance to use for communicating OLE drag and drop information for the specified window.

Return Values
S_OK

Indicates the application was registered successfully.

DRAGDROP_E_INVALIDHWND

Indicates invalid handle returned in the hwnd parameter.

DRAGDROP_E_ALREADYREGISTERED

Indicates the specified window has already been registered as a drop target.

E_OUTOFMEMORY

Indicates out of memory.

Comments
If your application can accept dropped objects during OLE drag and drop operations, you must call the RegisterDragDrop function. Do this whenever one of your application windows is available as a potential drop target, i.e., when the window appears unobscured on the screen.

The RegisterDragDrop function only registers one window at a time, so you must call it for each application window capable of accepting dropped objects.

As the mouse passes over unobscured portions of the target window during an OLE drag and drop operation, the DoDragDrop function calls the specified IDropTarget::DragOver method for the current window. When a drop operation actually occurs in a given window, the DoDragDrop function calls IDropTarget::Drop.

The RegisterDragDrop function also calls the IUnknown::AddRef method for your drop target interface.