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SWT is an open source widget toolkit for Java designed to provide efficient, portable access to the user-interface facilities of the operating systems on which it is implemented.
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/*******************************************************************************
 * Copyright (c) 2000, 2011 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.swt.dnd;

import org.eclipse.swt.internal.cocoa.*;
import org.eclipse.swt.widgets.*;

/**
 * This class provides a default drag under effect (eg. select, insert, scroll and expand) 
 * when a drag occurs over a Tree.
 * 
 * Classes that wish to provide their own drag under effect for a Tree
 * can extend the TreeDropTargetEffect class and override any applicable methods 
 * in TreeDropTargetEffect to display their own drag under effect.
 *
 * Subclasses that override any methods of this class must call the corresponding
 * super method to get the default drag under effect implementation.
 *
 * The feedback value is either one of the FEEDBACK constants defined in 
 * class DND which is applicable to instances of this class, 
 * or it must be built by bitwise OR'ing together 
 * (that is, using the int "|" operator) two or more
 * of those DND effect constants. 
 * 
 * 
 * 

 * Feedback:
 * FEEDBACK_SELECT, FEEDBACK_INSERT_BEFORE, FEEDBACK_INSERT_AFTER, FEEDBACK_EXPAND, FEEDBACK_SCROLL
 * 
 * 

 * Note: Only one of the styles FEEDBACK_SELECT, FEEDBACK_INSERT_BEFORE or
 * FEEDBACK_INSERT_AFTER may be specified.
 * 
 * 
 * @see DropTargetAdapter
 * @see DropTargetEvent
 * @see Sample code and further information
 * 
 * @since 3.3
 */
public class TreeDropTargetEffect extends DropTargetEffect {
	boolean shouldEnableScrolling;

	/**
	 * Creates a new TreeDropTargetEffect to handle the drag under effect on the specified 
	 * Tree.
	 * 
	 * @param tree the Tree over which the user positions the cursor to drop the data
	 */
	public TreeDropTargetEffect(Tree tree) {
		super(tree);
	}

	int checkEffect(int effect) {
		// Some effects are mutually exclusive.  Make sure that only one of the mutually exclusive effects has been specified.
		if ((effect & DND.FEEDBACK_SELECT) != 0) effect = effect & ~DND.FEEDBACK_INSERT_AFTER & ~DND.FEEDBACK_INSERT_BEFORE;
		if ((effect & DND.FEEDBACK_INSERT_BEFORE) != 0) effect = effect & ~DND.FEEDBACK_INSERT_AFTER;
		return effect;
	}

	/**
	 * This implementation of dragEnter provides a default drag under effect
	 * for the feedback specified in event.feedback.
	 * 
	 * For additional information see DropTargetAdapter.dragEnter.
	 * 
	 * Subclasses that override this method should call super.dragEnter(event)
	 * to get the default drag under effect implementation.
	 *
	 * @param event  the information associated with the drag enter event
	 * 
	 * @see DropTargetAdapter
	 * @see DropTargetEvent
	 */
	public void dragEnter(DropTargetEvent event) {
	}

	/**
	 * This implementation of dragLeave provides a default drag under effect
	 * for the feedback specified in event.feedback.
	 * 
	 * For additional information see DropTargetAdapter.dragLeave.
	 * 
	 * Subclasses that override this method should call super.dragLeave(event)
	 * to get the default drag under effect implementation.
	 *
	 * @param event  the information associated with the drag leave event
	 * 
	 * @see DropTargetAdapter
	 * @see DropTargetEvent
	 */
	public void dragLeave(DropTargetEvent event) {
		OS.objc_msgSend(control.view.id, OS.sel_setShouldExpandItem_, 1);
		if (shouldEnableScrolling) {
			shouldEnableScrolling = false;
			OS.objc_msgSend(control.view.id, OS.sel_setShouldScrollClipView_, 1);
			control.redraw();
		}
	}

	/**
	 * This implementation of dragOver provides a default drag under effect
	 * for the feedback specified in event.feedback.
	 * 
	 * For additional information see DropTargetAdapter.dragOver.
	 * 
	 * Subclasses that override this method should call super.dragOver(event)
	 * to get the default drag under effect implementation.
	 *
	 * @param event  the information associated with the drag over event
	 * 
	 * @see DropTargetAdapter
	 * @see DropTargetEvent
	 * @see DND#FEEDBACK_SELECT
	 * @see DND#FEEDBACK_INSERT_BEFORE
	 * @see DND#FEEDBACK_INSERT_AFTER
	 * @see DND#FEEDBACK_SCROLL
	 */
	public void dragOver(DropTargetEvent event) {
		int effect = checkEffect(event.feedback);		
		((DropTarget)event.widget).feedback = effect;
		OS.objc_msgSend(control.view.id, OS.sel_setShouldExpandItem_, (effect & DND.FEEDBACK_EXPAND) == 0 ? 0 : 1);
		if ((effect & DND.FEEDBACK_SCROLL) == 0) {
			shouldEnableScrolling = true;
			OS.objc_msgSend(control.view.id, OS.sel_setShouldScrollClipView_, 0);
		} else {
			OS.objc_msgSend(control.view.id, OS.sel_setShouldScrollClipView_, 1);
		}
	}
}