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Eclipse Platform
Release 3.5

org.eclipse.jface.util
Class DelegatingDropAdapter

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

public class DelegatingDropAdapter
extends Object
implements DropTargetListener

A DelegatingDropAdapter is a DropTargetListener that maintains and delegates to a set of TransferDropTargetListeners. Each TransferDropTargetListener can then be implemented as if it were the DropTarget's only DropTargetListener.

On dragEnter, dragOperationChanged, dragOver and drop, a current listener is obtained from the set of all TransferDropTargetListeners. The current listener is the first listener to return true for TransferDropTargetListener.isEnabled(DropTargetEvent). The current listener is forwarded all DropTargetEvents until some other listener becomes the current listener, or the drop terminates.

After adding all TransferDropTargetListeners to the DelegatingDropAdapter the combined set of Transfers should be set in the SWT DropTarget. #getTransfers() provides the set of Transfer types of all TransferDropTargetListeners.

The following example snippet shows a DelegatingDropAdapter with two TransferDropTargetListeners. One supports dropping resources and demonstrates how a listener can be disabled in the isEnabled method. The other listener supports text transfer.

                final TreeViewer viewer = new TreeViewer(shell, SWT.NONE);
                DelegatingDropAdapter dropAdapter = new DelegatingDropAdapter();
                dropAdapter.addDropTargetListener(new TransferDropTargetListener() {
                        public Transfer getTransfer() {
                                return ResourceTransfer.getInstance();
                        }
                        public boolean isEnabled(DropTargetEvent event) {
                                // disable drop listener if there is no viewer selection
                                if (viewer.getSelection().isEmpty())
                                        return false;
                                return true;
                        }
                        public void dragEnter(DropTargetEvent event) {}
                        public void dragLeave(DropTargetEvent event) {}
                        public void dragOperationChanged(DropTargetEvent event) {}
                        public void dragOver(DropTargetEvent event) {}
                        public void drop(DropTargetEvent event) {
                                if (event.data == null)
                                        return;
                                IResource[] resources = (IResource[]) event.data;
                                if (event.detail == DND.DROP_COPY) {
                                        // copy resources
                                } else {
                                        // move resources
                                }
                                        
                        }
                        public void dropAccept(DropTargetEvent event) {}
                });
                dropAdapter.addDropTargetListener(new TransferDropTargetListener() {
                        public Transfer getTransfer() {
                                return TextTransfer.getInstance();
                        }
                        public boolean isEnabled(DropTargetEvent event) {
                                return true;
                        }
                        public void dragEnter(DropTargetEvent event) {}
                        public void dragLeave(DropTargetEvent event) {}
                        public void dragOperationChanged(DropTargetEvent event) {}
                        public void dragOver(DropTargetEvent event) {}
                        public void drop(DropTargetEvent event) {
                                if (event.data == null)
                                        return;
                                System.out.println(event.data);
                        }
                        public void dropAccept(DropTargetEvent event) {}
                });             
                viewer.addDropSupport(DND.DROP_COPY | DND.DROP_MOVE, dropAdapter.getTransfers(), dropAdapter);
 

Since:
3.0

Constructor Summary
DelegatingDropAdapter ()
           
 
Method Summary
 void addDropTargetListener ( TransferDropTargetListener listener)
          Adds the given TransferDropTargetListener.
 void dragEnter ( DropTargetEvent event)
          The cursor has entered the drop target boundaries.
 void dragLeave ( DropTargetEvent event)
          The cursor has left the drop target boundaries.
 void dragOperationChanged ( DropTargetEvent event)
          The operation being performed has changed (usually due to the user changing a drag modifier key while dragging).
 void dragOver ( DropTargetEvent event)
          The cursor is moving over the drop target.
 void drop ( DropTargetEvent event)
          Forwards this event to the current listener, if there is one.
 void dropAccept ( DropTargetEvent event)
          Forwards this event to the current listener if there is one.
  Transfer[] getTransfers ()
          Returns the combined set of Transfer types of all TransferDropTargetListeners.
 boolean isEmpty ()
          Returns true if there are no listeners to delegate events to.
 void removeDropTargetListener ( TransferDropTargetListener listener)
          Removes the given TransferDropTargetListener.
 
Methods inherited from class java.lang. Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 

Constructor Detail

DelegatingDropAdapter

public DelegatingDropAdapter()
Method Detail

addDropTargetListener

public void addDropTargetListener(
TransferDropTargetListener listener)
Adds the given TransferDropTargetListener.

Parameters:
listener - the new listener

dragEnter

public void dragEnter(
DropTargetEvent event)
The cursor has entered the drop target boundaries. The current listener is updated, and #dragEnter() is forwarded to the current listener.

Specified by:
dragEnter in interface DropTargetListener
Parameters:
event - the drop target event
See Also:
DropTargetListener.dragEnter(DropTargetEvent)

dragLeave

public void dragLeave(
DropTargetEvent event)
The cursor has left the drop target boundaries. The event is forwarded to the current listener.

Specified by:
dragLeave in interface DropTargetListener
Parameters:
event - the drop target event
See Also:
DropTargetListener.dragLeave(DropTargetEvent)

dragOperationChanged

public void dragOperationChanged(
DropTargetEvent event)
The operation being performed has changed (usually due to the user changing a drag modifier key while dragging). Updates the current listener and forwards this event to that listener.

Specified by:
dragOperationChanged in interface DropTargetListener
Parameters:
event - the drop target event
See Also:
DropTargetListener.dragOperationChanged(DropTargetEvent)

dragOver

public void dragOver(
DropTargetEvent event)
The cursor is moving over the drop target. Updates the current listener and forwards this event to that listener. If no listener can handle the drag operation the event.detail field is set to DND.DROP_NONE to indicate an invalid drop.

Specified by:
dragOver in interface DropTargetListener
Parameters:
event - the drop target event
See Also:
DropTargetListener.dragOver(DropTargetEvent)

drop

public void drop(
DropTargetEvent event)
Forwards this event to the current listener, if there is one. Sets the current listener to null afterwards.

Specified by:
drop in interface DropTargetListener
Parameters:
event - the drop target event
See Also:
DropTargetListener.drop(DropTargetEvent)

dropAccept

public void dropAccept(
DropTargetEvent event)
Forwards this event to the current listener if there is one.

Specified by:
dropAccept in interface DropTargetListener
Parameters:
event - the drop target event
See Also:
DropTargetListener.dropAccept(DropTargetEvent)

getTransfers

public 
Transfer[] getTransfers()
Returns the combined set of Transfer types of all TransferDropTargetListeners.

Returns:
the combined set of Transfer types

isEmpty

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

Returns:
true if there are no TransferDropTargetListeners false otherwise

removeDropTargetListener

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

Parameters:
listener - the listener to remove

Eclipse Platform
Release 3.5

Guidelines for using Eclipse APIs.

Copyright (c) Eclipse contributors and others 2000, 2008. All rights reserved.


 
 
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