Adds the listener to the collection of listeners who will
be notified when a drag and drop operation is in progress, by sending
it one of the messages defined in the <code>DragSourceListener</code>
interface.
<p><ul>
<li><code>dragStart</code> is called when 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.
<li><code>dragSetData</code> is called when the data is required from the drag source.
<li><code>dragFinished</code> is called when 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.
</ul></p>
@param listener the listener which should be notified
@exception IllegalArgumentException <ul>
<li>ERROR_NULL_ARGUMENT - if the listener is null</li>
</ul>
@exception SWTException <ul>
<li>ERROR_WIDGET_DISPOSED - if the receiver has been disposed</li>
<li>ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver</li>
</ul>
Adds the listener to the collection of listeners who will be notified when a drag and drop operation is in progress, by sending it one of the messages defined in the <code>DragSourceListener</code> interface.
<p><ul> <li><code>dragStart</code> is called when 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. <li><code>dragSetData</code> is called when the data is required from the drag source. <li><code>dragFinished</code> is called when 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. </ul></p>
@param listener the listener which should be notified
@exception IllegalArgumentException <ul> <li>ERROR_NULL_ARGUMENT - if the listener is null</li> </ul> @exception SWTException <ul> <li>ERROR_WIDGET_DISPOSED - if the receiver has been disposed</li> <li>ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver</li> </ul>
@see DragSourceListener @see #getDragListeners @see #removeDragListener @see DragSourceEvent