The drop has successfully completed(mouse up over a valid target) or has been terminated (such as hitting the ESC key). Perform cleanup such as removing data from the source side on a successful move operation.
The data is required from the drag source.
The user has begun the actions required to drag the widget. This event gives the application the chance to decide if a drag should be started.
The <code>DragSourceListener</code> class provides event notification to the application for DragSource events.
<p>When the user drops data on a <code>DropTarget</code>, the application which defines the <code>DragSource</code> must provide the dropped data by implementing <code>dragSetData</code>. In the dragSetData, the application must support all the data types that were specified in the DragSource#setTransfer method.</p>
<p>After the drop has completed successfully or has been aborted, the application which defines the <code>DragSource</code> is required to take the appropriate cleanup action. In the case of a successful <b>move</b> operation, the application must remove the data that was transferred.</p>