LayoutListener.java

/*******************************************************************************
 * Copyright (c) 2004, 2005 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.draw2d;

/**
 * Classes which implement this interface provide callback hooks for various layout
 * related events.
 * <P>
 * Instances can be hooked to figures by calling {@link
 * IFigure#addLayoutListener(LayoutListener)}. Listeners will be made aware of various
 * steps of the layout mechanism, and even have the opportunity to prevent normal layout
 * from occurring.
 * @since 3.1
 */
public interface LayoutListener {

/**
 * A stub implementation which implements all of the declared methods. 
 * @since 3.1
 */
class Stub implements LayoutListener {

	/**
	 * Stub which does nothing.
	 * @see LayoutListener#invalidate(IFigure)
	 */
	public void invalidate(IFigure container) { }
	
	/**
	 * Stub which does nothing.
	 * @see LayoutListener#layout(IFigure)
	 */
	public boolean layout(IFigure container) {
		return false;
	}

	/**
	 * Stub which does nothing.
	 * @see LayoutListener#postLayout(IFigure)
	 */
	public void postLayout(IFigure container) { }

	/**
	 * Stub which does nothing.
	 * @see LayoutListener#remove(IFigure)
	 */
	public void remove(IFigure child) { }

	/**
	 * Stub which does nothing.
	 * @see LayoutListener#setConstraint(IFigure, java.lang.Object)
	 */
	public void setConstraint(IFigure child, Object constraint) { }
	
}

/**
 * Called when a container has been invalidated.
 * @param container the invalidated Figure
 * @since 3.1
 */
void invalidate(IFigure container);

/**
 * Called prior to layout occurring.  A listener may intercept a layout by
 * returning <code>true</code>.  If the layout is intercepted, the container's
 * <code>LayoutManager</code> will not receive a layout call.
 * @param container the figure incurring a layout
 * @return <code>true</code> if the layout has been intercepted by the listener
 * @since 3.1
 */
boolean layout(IFigure container);

/**
 * Called after layout has occurred.
 * @since 3.1
 * @param container the figure incurring a layout 
 */
void postLayout(IFigure container);

/**
 * Called when a child is about to be removed from its parent.
 * @since 3.1
 * @param child the child being removed
 */
void remove(IFigure child);

/**
 * Called when a child's constraint is initialized or updated.
 * @param child the child being updated
 * @param constraint the child's new constraint
 * @since 3.1
 */
void setConstraint(IFigure child, Object constraint);

}