LayoutListener.java

/*******************************************************************************
 * Copyright (c) 2004, 2010 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);

}