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/*******************************************************************************
 * Copyright (c) 2000, 2017 IBM Corporation and others.
 *
 * 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 Corporation - initial API and implementation
 *******************************************************************************/
package org.eclipse.swt.dnd;

import org.eclipse.swt.graphics.*;
import org.eclipse.swt.widgets.*;

/**
 * This class provides default implementations to display a source image
 * when a drag is initiated from a Tree.
 *
 * Classes that wish to provide their own source image for a Tree can
 * extend TreeDragSourceEffect class and override the TreeDragSourceEffect.dragStart
 * method and set the field DragSourceEvent.image with their own image.
 *
 * Subclasses that override any methods of this class must call the corresponding
 * super method to get the default drag under effect implementation.
 *
 * @see DragSourceEffect
 * @see DragSourceEvent
 * @see Sample code and further information
 *
 * @since 3.3
 */
public class TreeDragSourceEffect extends DragSourceEffect {
	Image dragSourceImage = null;

	/**
	 * Creates a new TreeDragSourceEffect to handle drag effect
	 * from the specified Tree.
	 *
	 * @param tree the Tree that the user clicks on to initiate the drag
	 */
	public TreeDragSourceEffect(Tree tree) {
		super(tree);
	}

	/**
	 * This implementation of dragFinished disposes the image
	 * that was created in TreeDragSourceEffect.dragStart.
	 *
	 * Subclasses that override this method should call super.dragFinished(event)
	 * to dispose the image in the default implementation.
	 *
	 * @param event the information associated with the drag finished event
	 */
	@Override
	public void dragFinished(DragSourceEvent event) {
		if (dragSourceImage != null) dragSourceImage.dispose();
		dragSourceImage = null;
	}

	/**
	 * This implementation of dragStart will create a default
	 * image that will be used during the drag. The image should be disposed
	 * when the drag is completed in the TreeDragSourceEffect.dragFinished
	 * method.
	 *
	 * Subclasses that override this method should call super.dragStart(event)
	 * to use the image from the default implementation.
	 *
	 * @param event the information associated with the drag start event
	 */
	@Override
	public void dragStart(DragSourceEvent event) {
		event.image = getDragSourceImage(event);
	}

	Image getDragSourceImage(DragSourceEvent event) {
		if (dragSourceImage != null) dragSourceImage.dispose();
		dragSourceImage = TreeTableCommon.getDragSourceImage(control);
		return dragSourceImage;
	}
}