ViewerDragAdapter.java

/**
 * <copyright> 
 *
 * Copyright (c) 2002, 2009 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 - Initial API and implementation
 *
 * </copyright>
 *
 * $Id: ViewerDragAdapter.java,v 1.5 2007/06/14 18:32:37 emerks Exp $
 */
package net.enilink.komma.edit.ui.dnd;

import org.eclipse.jface.viewers.ISelection;
import org.eclipse.jface.viewers.Viewer;
import org.eclipse.swt.dnd.DragSourceEvent;
import org.eclipse.swt.dnd.DragSourceListener;

/**
 * This is an implementation of {@link DragSourceListener}. It allows the
 * selection in effect at the start of the drag and drop interaction to be
 * recorded, which is especially important for a drag and drop interaction
 * within a single view. This is how one of these adapters is typically hooked
 * up:
 * 
 * <pre>
 * viewer.addDragSupport(DND.DROP_COPY | DND.DROP_MOVE | DND.DROP_LINK,
 * 		new Transfer[] { LocalTransfer.getInstance() },
 * 		ViewerDragAdapter(viewer));
 * </pre>
 * 
 * Doing so simply allows a drag operation to be initiated from the viewer such
 * that the viewer's selection is transferred to the drop target. See
 * {@link EditingDomainViewerDropAdapter} and {@link LocalTransfer} for more
 * details.
 */
public class ViewerDragAdapter implements DragSourceListener {
	/**
	 * This keeps track of the viewer to which we are listening.
	 */
	protected Viewer viewer;

	/**
	 * This keeps track of the selection that is in effect at the start of the
	 * drag operation
	 */
	protected ISelection selection;

	/**
	 * This creates an instance for the given viewer.
	 */
	public ViewerDragAdapter(Viewer viewer) {
		super();

		// Remember the viewer and listen to SWT.DragDetect to alert the start
		// of the drag operation.
		//
		this.viewer = viewer;
	}

	/**
	 * This is called when dragging is initiated; it records the
	 * {@link #selection} of {@link #viewer}.
	 */
	public void dragStart(DragSourceEvent event) {
		selection = viewer.getSelection();
	}

	/**
	 * This is called when dragging is completed; it forgets the
	 * {@link #selection}.
	 */
	public void dragFinished(DragSourceEvent event) {
		selection = null;
		LocalTransfer.getInstance().javaToNative(null, null);
	}

	/**
	 * This is called to transfer the data.
	 */
	public void dragSetData(DragSourceEvent event) {
		if (LocalTransfer.getInstance().isSupportedType(event.dataType)) {
			event.data = selection;
		}
	}
}