org.eclipse.jdt.ui/ui/org/eclipse/jdt/internal/ui/dnd/DelegatingDragAdapter.java

/*******************************************************************************
 * Copyright (c) 2000, 2005 IBM Corporation and others.
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/epl-v10.html
 *
 * Contributors:
 *     IBM Corporation - initial API and implementation
 *******************************************************************************/
package org.eclipse.jdt.internal.ui.dnd;

import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;

import org.eclipse.swt.dnd.DragSource;
import org.eclipse.swt.dnd.DragSourceEvent;
import org.eclipse.swt.dnd.DragSourceListener;
import org.eclipse.swt.dnd.Transfer;
import org.eclipse.swt.dnd.TransferData;

import org.eclipse.jface.util.Assert;
import org.eclipse.jface.util.TransferDragSourceListener;

/**
 * A delegating drag adapter negotiates between a set of <code>TransferDragSourceListener</code>s
 * On <code>dragStart</code> the adapter determines the listener to be used for any further
 * <code>drag*</code> callback.
 */
public class DelegatingDragAdapter implements DragSourceListener {

	private TransferDragSourceListener[] fPossibleListeners;
	private List fActiveListeners;
	private TransferDragSourceListener fFinishListener;
	
	public DelegatingDragAdapter(TransferDragSourceListener[] listeners) {
		setPossibleListeners(listeners);
	}
	
	protected void setPossibleListeners(TransferDragSourceListener[] listeners) {
		Assert.isNotNull(listeners);
		Assert.isTrue(fActiveListeners == null, "Can only set possible listeners before drag operation has started"); //$NON-NLS-1$
		fPossibleListeners= listeners;
	}
	
	/* non Java-doc
	 * @see DragSourceListener
	 */
	public void dragStart(DragSourceEvent event) {
		fFinishListener= null;
		boolean saveDoit= event.doit;
		Object saveData= event.data;
		boolean doIt= false;
		List transfers= new ArrayList(fPossibleListeners.length);
		fActiveListeners= new ArrayList(fPossibleListeners.length);
		
		for (int i= 0; i < fPossibleListeners.length; i++) {
			TransferDragSourceListener listener= fPossibleListeners[i];
			event.doit= saveDoit;
			listener.dragStart(event);
			if (event.doit) {
				transfers.add(listener.getTransfer());
				fActiveListeners.add(listener);
			}
			doIt= doIt || event.doit;
		}
		if (doIt) {
			((DragSource)event.widget).setTransfer((Transfer[])transfers.toArray(new Transfer[transfers.size()]));
		}
		event.data= saveData;
		event.doit= doIt;
	}

	/* non Java-doc
	 * @see DragSourceListener
	 */
	public void dragSetData(DragSourceEvent event) {
		fFinishListener= getListener(event.dataType);
		if (fFinishListener != null)
			fFinishListener.dragSetData(event);
	}
	
	/* non Java-doc
	 * @see DragSourceListener
	 */
	public void dragFinished(DragSourceEvent event) {
		try{
			if (fFinishListener != null) {
				fFinishListener.dragFinished(event);
			} else {
				// If the user presses Escape then we get a dragFinished without
				// getting a dragSetData before.
				fFinishListener= getListener(event.dataType);
				if (fFinishListener != null)
					fFinishListener.dragFinished(event);
			}
		} finally{
			fFinishListener= null;
			fActiveListeners= null;
		}	
	}
	
	private TransferDragSourceListener getListener(TransferData type) {
		if (type == null)
			return null;
			
		for (Iterator iter= fActiveListeners.iterator(); iter.hasNext();) {
			TransferDragSourceListener listener= (TransferDragSourceListener)iter.next();
			if (listener.getTransfer().isSupportedType(type)) {
				return listener;
			}
		}
		return null;
	}	
}