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Eclipse Platform
Release 3.5

org.eclipse.jface.util
Class DelegatingDragAdapter

java.lang.Object
  extended by 
org.eclipse.jface.util.DelegatingDragAdapter
All Implemented Interfaces:
EventListener, DragSourceListener, org.eclipse.swt.internal.SWTEventListener

public class DelegatingDragAdapter
extends Object
implements DragSourceListener

A DelegatingDragAdapter is a DragSourceListener that maintains and delegates to a set of TransferDragSourceListeners. Each TransferDragSourceListener can then be implemented as if it were the DragSource's only DragSourceListener.

When a drag is started, a subset of all TransferDragSourceListeners is generated and stored in a list of active listeners. This subset is calculated by forwarding DragSourceListener.dragStart(DragSourceEvent) to every listener, and checking if the doit field is left set to true.

The DragSource's set of supported Transfer types ( DragSource.setTransfer(Transfer[])) is updated to reflect the Transfer types corresponding to the active listener subset.

If and when dragSetData(DragSourceEvent) is called, a single TransferDragSourceListener is chosen, and only it is allowed to set the drag data. The chosen listener is the first listener in the subset of active listeners whose Transfer supports ( Transfer.isSupportedType(TransferData)) the dataType in the DragSourceEvent.

The following example snippet shows a DelegatingDragAdapter with two TransferDragSourceListeners. One implements drag of text strings, the other supports file transfer and demonstrates how a listener can be disabled using the dragStart method.

                final TreeViewer viewer = new TreeViewer(shell, SWT.NONE);
                
                DelegatingDragAdapter dragAdapter = new DelegatingDragAdapter();                
                dragAdapter.addDragSourceListener(new TransferDragSourceListener() {
                        public Transfer getTransfer() {
                                return TextTransfer.getInstance();
                        }
                        public void dragStart(DragSourceEvent event) {
                                // always enabled, can control enablement based on selection etc.
                        }
                        public void dragSetData(DragSourceEvent event) {
                                event.data = "Transfer data";
                        }
                        public void dragFinished(DragSourceEvent event) {
                                // no clean-up required
                        }
                });
                dragAdapter.addDragSourceListener(new TransferDragSourceListener() {
                        public Transfer getTransfer() {
                                return FileTransfer.getInstance();
                        }
                        public void dragStart(DragSourceEvent event) {
                                // enable drag listener if there is a viewer selection
                                event.doit = !viewer.getSelection().isEmpty();
                        }
                        public void dragSetData(DragSourceEvent event) {
                                File file1 = new File("C:/temp/file1");
                                File file2 = new File("C:/temp/file2");
                                event.data = new String[] {file1.getAbsolutePath(), file2.getAbsolutePath()};
                        }
                        public void dragFinished(DragSourceEvent event) {
                                // no clean-up required
                        }
                });
                viewer.addDragSupport(DND.DROP_COPY | DND.DROP_MOVE, dragAdapter.getTransfers(), dragAdapter);
 

Since:
3.0

Constructor Summary
DelegatingDragAdapter ()
           
 
Method Summary
 void addDragSourceListener ( TransferDragSourceListener listener)
          Adds the given TransferDragSourceListener.
 void dragFinished ( DragSourceEvent event)
          The drop has successfully completed.
 void dragSetData ( DragSourceEvent event)
          The drop data is requested.
 void dragStart ( DragSourceEvent event)
          A drag operation has started.
  Transfer[] getTransfers ()
          Returns the Transfers from every TransferDragSourceListener.
 boolean isEmpty ()
          Returns true if there are no listeners to delegate drag events to.
 void removeDragSourceListener ( TransferDragSourceListener listener)
          Removes the given TransferDragSourceListener.
 
Methods inherited from class java.lang. Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 

Constructor Detail

DelegatingDragAdapter

public DelegatingDragAdapter()
Method Detail

addDragSourceListener

public void addDragSourceListener(
TransferDragSourceListener listener)
Adds the given TransferDragSourceListener.

Parameters:
listener - the new listener

dragFinished

public void dragFinished(
DragSourceEvent event)
The drop has successfully completed. This event is forwarded to the current drag listener. Doesn't update the current listener, since the current listener is already the one that completed the drag operation.

Specified by:
dragFinished in interface DragSourceListener
Parameters:
event - the drag source event
See Also:
DragSourceListener.dragFinished(DragSourceEvent)

dragSetData

public void dragSetData(
DragSourceEvent event)
The drop data is requested. Updates the current listener and then forwards the event to it.

Specified by:
dragSetData in interface DragSourceListener
Parameters:
event - the drag source event
See Also:
DragSourceListener.dragSetData(DragSourceEvent)

dragStart

public void dragStart(
DragSourceEvent event)
A drag operation has started. Forwards this event to each listener. A listener must set event.doit to false if it cannot handle the drag operation. If a listener can handle the drag, it is added to the list of active listeners. The drag is aborted if there are no listeners that can handle it.

Specified by:
dragStart in interface DragSourceListener
Parameters:
event - the drag source event
See Also:
DragSourceListener.dragStart(DragSourceEvent)

getTransfers

public 
Transfer[] getTransfers()
Returns the Transfers from every TransferDragSourceListener.

Returns:
the combined Transfers

isEmpty

public boolean isEmpty()
Returns true if there are no listeners to delegate drag events to.

Returns:
true if there are no TransferDragSourceListeners false otherwise.

removeDragSourceListener

public void removeDragSourceListener(
TransferDragSourceListener listener)
Removes the given TransferDragSourceListener. Listeners should not be removed while a drag and drop operation is in progress.

Parameters:
listener - the TransferDragSourceListener to remove

Eclipse Platform
Release 3.5

Guidelines for using Eclipse APIs.

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