bundles/org.eclipse.gef/src/org/eclipse/gef/dnd/TemplateTransferDragSourceListener.java

/*******************************************************************************
 * Copyright (c) 2000, 2010 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.gef.dnd;

import java.util.List;

import org.eclipse.swt.dnd.DragSourceEvent;
import org.eclipse.swt.dnd.Transfer;

import org.eclipse.gef.EditPart;
import org.eclipse.gef.EditPartViewer;
import org.eclipse.gef.palette.CombinedTemplateCreationEntry;
import org.eclipse.gef.palette.PaletteTemplateEntry;

/**
 * Allows a single {@link PaletteTemplateEntry PaletteTemplateEntry} to be
 * dragged from an EditPartViewer. The PaletteTemplateEntry's <i>template</i>
 * object is the data that is being transfered to the <code>DropTarget</code>.
 * 
 * @since 2.1
 * @author Eric Bordeau
 */
public class TemplateTransferDragSourceListener extends
		AbstractTransferDragSourceListener {

	/**
	 * @deprecated Use the constructor without the transfer specified.
	 * @param viewer
	 *            viewer
	 * @param xfer
	 *            xfer
	 */
	public TemplateTransferDragSourceListener(EditPartViewer viewer,
			Transfer xfer) {
		super(viewer, xfer);
	}

	/**
	 * Constructs a new listener for the specified EditPartViewer. The provided
	 * Viewer should be one that is displaying a Palette. The
	 * TemplateTransferDragSourceListener will only be enabled when a single
	 * EditPart is selected, and the EditPart's model is a
	 * {@link PaletteTemplateEntry}.
	 * 
	 * @param viewer
	 *            the EditPartViewer that is the drag source
	 */
	public TemplateTransferDragSourceListener(EditPartViewer viewer) {
		super(viewer, TemplateTransfer.getInstance());
	}

	/**
	 * @see AbstractTransferDragSourceListener#dragFinished(DragSourceEvent)
	 */
	public void dragFinished(DragSourceEvent event) {
		TemplateTransfer.getInstance().setTemplate(null);
	}

	/**
	 * Get the <i>template</i> from the selected {@link PaletteTemplateEntry}
	 * and sets it as the event data to be dropped.
	 * 
	 * @param event
	 *            the DragSourceEvent
	 */
	public void dragSetData(DragSourceEvent event) {
		event.data = getTemplate();
	}

	/**
	 * Cancels the drag if the selected item does not represent a
	 * PaletteTemplateEntry.
	 * 
	 * @see org.eclipse.swt.dnd.DragSourceListener#dragStart(DragSourceEvent)
	 */
	public void dragStart(DragSourceEvent event) {
		Object template = getTemplate();
		if (template == null)
			event.doit = false;
		TemplateTransfer.getInstance().setTemplate(template);
	}

	/**
	 * A helper method that returns <code>null</code> or the <i>template</i>
	 * Object from the currently selected EditPart.
	 * 
	 * @return the template
	 */
	protected Object getTemplate() {
		List selection = getViewer().getSelectedEditParts();
		if (selection.size() == 1) {
			EditPart editpart = (EditPart) getViewer().getSelectedEditParts()
					.get(0);
			Object model = editpart.getModel();
			if (model instanceof PaletteTemplateEntry)
				return ((PaletteTemplateEntry) model).getTemplate();
			if (model instanceof CombinedTemplateCreationEntry)
				return ((CombinedTemplateCreationEntry) model).getTemplate();
		}
		return null;
	}

}