bundles/org.eclipse.swt/Eclipse SWT Drag and Drop/gtk/org/eclipse/swt/dnd/TableDragSourceEffect.java

/*******************************************************************************
 * Copyright (c) 2000, 2018 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 <code>Table</code>.
 *
 * <p>Classes that wish to provide their own source image for a <code>Table</code> can
 * extend the <code>TableDragSourceEffect</code> class, override the
 * <code>TableDragSourceEffect.dragStart</code> method and set the field
 * <code>DragSourceEvent.image</code> with their own image.</p>
 *
 * Subclasses that override any methods of this class must call the corresponding
 * <code>super</code> method to get the default drag source effect implementation.
 *
 * @see DragSourceEffect
 * @see DragSourceEvent
 * @see <a href="http://www.eclipse.org/swt/">Sample code and further information</a>
 *
 * @since 3.3
 */
public class TableDragSourceEffect extends DragSourceEffect {
	Image dragSourceImage = null;

	/**
	 * Creates a new <code>TableDragSourceEffect</code> to handle drag effect
	 * from the specified <code>Table</code>.
	 *
	 * @param table the <code>Table</code> that the user clicks on to initiate the drag
	 */
	public TableDragSourceEffect(Table table) {
		super(table);
	}

	/**
	 * This implementation of <code>dragFinished</code> disposes the image
	 * that was created in <code>TableDragSourceEffect.dragStart</code>.
	 *
	 * Subclasses that override this method should call <code>super.dragFinished(event)</code>
	 * 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 <code>dragStart</code> will create a default
	 * image that will be used during the drag. The image should be disposed
	 * when the drag is completed in the <code>TableDragSourceEffect.dragFinished</code>
	 * method.
	 *
	 * Subclasses that override this method should call <code>super.dragStart(event)</code>
	 * 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;
	}
}