Drag and Drop Operations - Win32 Programmer's Reference

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Drag and Drop Operations

A tree-view control notifies the parent window when the user starts to drag an item. The parent window receives a TVN_BEGINDRAG notification message when the user begins dragging an item with the left mouse button and a TVN_BEGINRDRAG notification message when the user begins dragging with the right button. You can prevent a tree-view control from sending these notifications by giving the tree-view control the TVS_DISABLEDRAGDROP style.

You obtain an image to display during a drag operation by using the TVM_CREATEDRAGIMAGE message. The tree-view control creates a dragging bitmap based on the label of the item being dragged. Then the tree-view control creates an image list, adds the bitmap to it, and returns the handle of the image list.

You must provide the code that actually drags the item. This typically involves using the dragging capabilities of the image list functions and processing the WM_MOUSEMOVE and WM_LBUTTONUP (or WM_RBUTTONUP) messages sent to the parent window after the drag operation has begun. For more information about the image list functions, see Image Lists. For more information about dragging a tree-view item, see Dragging a Tree-View Item.

If items in a tree-view control are to be the targets of a drag and drop operation, you need to know when the mouse cursor is on a target item. You can find out by using the TVM_HITTEST message. You specify the address of a TV_HITTESTINFO structure that contains the current coordinates of the mouse cursor. When the SendMessage function returns, the structure contains a flag indicating the location of the mouse cursor relative to the tree-view control. If the cursor is over an item in the tree-view control, the structure contains the handle of the item as well.

You can indicate that an item is the target of a drag and drop operation by using the TVM_SETITEM message to set the state to the TVIS_DROPHILITED value. An item that has this state is drawn in the style used to indicate a drag and drop target.

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