The Button property indicates the button that initiated the drag operation. The Button property is read-only. The drag operation can start if clicking with left or right mouse button any visible / selectable / dragable layer in the control. For instance, you can disable dragging with the right mouse button by changing the Change parameter of the DragStart event, to True, if the Button property is 2. The drag operation ends when the user releases the mouse button, or the user presses the ESC key. The DragEnd event notifies that the dragging the layer ends.