bundles/org.eclipse.draw2d/src/org/eclipse/draw2d/AbstractHintLayout.java

/*******************************************************************************
 * Copyright (c) 2000, 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;

import org.eclipse.draw2d.geometry.Dimension;

/**
 * The foundation for layout managers which are sensitive to width and/or height
 * hints. This class will cache preferred and minimum sizes for a given set of
 * hints. If the hints change in a meaningful way, the cached size is thrown out
 * and redetermined.
 * <P>
 * Subclasses may be sensitive to one or both hints. By default, this class
 * assumes both hints are important. Subclasses may override this behavior in
 * {@link #isSensitiveHorizontally(IFigure)} and
 * {@link #isSensitiveVertically(IFigure)}. At least one of these method should
 * return <code>true</code>.
 * 
 * @author hudsonr
 * @since 2.0
 */
public abstract class AbstractHintLayout extends AbstractLayout {

	private Dimension minimumSize = null;
	private Dimension cachedPreferredHint = new Dimension(-1, -1);
	private Dimension cachedMinimumHint = new Dimension(-1, -1);

	/**
	 * Calculates the minimum size using the given width and height hints. This
	 * method is called from {@link #getMinimumSize(IFigure, int, int)} whenever
	 * the cached minimum size has been flushed.
	 * <P>
	 * By default, this method just calls
	 * {@link #getPreferredSize(IFigure, int, int)}, meaning minimum and
	 * preferres sizes will be the same unless this method is overridden.
	 * 
	 * @param container
	 *            the Figure on which this layout is installed
	 * @param wHint
	 *            the width hint
	 * @param hHint
	 *            the height hint
	 * 
	 * @return the layout's minimum size
	 */
	protected Dimension calculateMinimumSize(IFigure container, int wHint,
			int hHint) {
		return getPreferredSize(container, wHint, hHint);
	}

	/**
	 * @see org.eclipse.draw2d.LayoutManager#getMinimumSize(IFigure, int, int)
	 */
	public Dimension getMinimumSize(IFigure container, int w, int h) {
		boolean flush = cachedMinimumHint.width != w
				&& isSensitiveHorizontally(container);
		flush |= cachedMinimumHint.height != h
				&& isSensitiveVertically(container);
		if (flush) {
			minimumSize = null;
			cachedMinimumHint.width = w;
			cachedMinimumHint.height = h;
		}
		if (minimumSize == null)
			minimumSize = calculateMinimumSize(container, w, h);
		return minimumSize;
	}

	/**
	 * @see org.eclipse.draw2d.LayoutManager#getPreferredSize(IFigure, int, int)
	 */
	public final Dimension getPreferredSize(IFigure container, int w, int h) {
		boolean flush = cachedPreferredHint.width != w
				&& isSensitiveHorizontally(container);
		flush |= cachedPreferredHint.height != h
				&& isSensitiveVertically(container);
		if (flush) {
			preferredSize = null;
			cachedPreferredHint.width = w;
			cachedPreferredHint.height = h;
		}
		return super.getPreferredSize(container, w, h);
	}

	/**
	 * Extends the superclass implementation to flush the cached minimum size.
	 * 
	 * @see org.eclipse.draw2d.LayoutManager#invalidate()
	 */
	public void invalidate() {
		minimumSize = null;
		super.invalidate();
	}

	/**
	 * Returns whether this layout manager is sensitive to changes in the
	 * horizontal hint. By default, this method returns <code>true</code>.
	 * 
	 * @param container
	 *            the layout's container
	 * @return <code>true</code> if this layout is sensite to horizontal hint
	 *         changes
	 */
	protected boolean isSensitiveHorizontally(IFigure container) {
		return true;
	}

	/**
	 * Returns whether this layout manager is sensitive to changes in the
	 * vertical hint. By default, this method returns <code>true</code>.
	 * 
	 * @param container
	 *            the layout's container
	 * @return <code>true</code> if this layout is sensite to vertical hint
	 *         changes
	 */
	protected boolean isSensitiveVertically(IFigure container) {
		return true;
	}

}