bundles/org.eclipse.emf.rap.edit.ui.minimal/src/org/eclipse/emf/edit/ui/dnd/ViewerDragAdapter.java

/**
 * Copyright (c) 2002-2006 IBM Corporation and others.
 * 
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License 2.0
 * which accompanies this distribution, and is available at
 * https://www.eclipse.org/legal/epl-2.0/
 *
 * SPDX-License-Identifier: EPL-2.0
 *
 * Contributors:
 * IBM - Initial API and implementation
 */
// REUSED CLASS
package org.eclipse.emf.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
{
	private static final long serialVersionUID = 1L;

	/**
	 * 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}.
	 */
	@Override
	public void dragStart(DragSourceEvent event)
	{
		selection = viewer.getSelection();
	}

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

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