org.eclipse.swt.widgets.Layout.java Source code

Introduction

Here is the source code for org.eclipse.swt.widgets.Layout.java

Source

/*******************************************************************************
 * Copyright (c) 2002, 2007 Innoopract Informationssysteme GmbH.
 * 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:
 *     Innoopract Informationssysteme GmbH - initial API and implementation
 ******************************************************************************/
package org.eclipse.swt.widgets;

import org.eclipse.swt.graphics.Point;
import org.eclipse.swt.internal.SerializableCompatibility;

/**
 * A layout controls the position and size of the children of a composite
 * widget. This class is the abstract base class for layouts.
 * 
 * @see Composite#setLayout(Layout)
 */
public abstract class Layout implements SerializableCompatibility {

    /**
      * Lays out the children of the specified composite according to this
      * layout.
      * <p>
      * This method positions and sizes the children of a composite using the
      * layout algorithm encoded by this layout. Children of the composite are
      * positioned in the client area of the composite. The position of the
      * composite is not altered by this method.
      * </p>
      * <p>
      * When the flush cache hint is true, the layout is instructed to flush any
      * cached values associated with the children. Typically, a layout will
      * cache the preferred sizes of the children to avoid the expense of
      * computing these values each time the widget is laid out.
      * </p>
      * <p>
      * When layout is triggered explicitly by the programmer the flush cache
      * hint is true. When layout is triggered by a resize, either caused by the
      * programmer or by the user, the hint is false.
      * </p>
      * 
      * @param composite
      *            a composite widget using this layout
      * @param flushCache
      *            <code>true</code> means flush cached layout values
      */
    protected abstract void layout(Composite composite, boolean flushCache);

    /**
     * Instruct the layout to flush any cached values
     * associated with the control specified in the argument 
     * <code>control</code>.
     * 
     * @param control a control managed by this layout
     * @return true if the Layout has flushed all cached information associated with control
     */
    protected boolean flushCache(Control control) {
        return false;
    }

    /**
     * Computes and returns the size of the specified composite's client area
     * according to this layout.
     * <p>
     * This method computes the size that the client area of the composite must
     * be in order to position all children at their preferred size inside the
     * composite according to the layout algorithm encoded by this layout.
     * </p>
     * <p>
     * When a width or height hint is supplied, it is used to constrain the
     * result. For example, if a width hint is provided that is less than the
     * width of the client area, the layout may choose to wrap and increase
     * height, clip, overlap, or otherwise constrain the children.
     * </p>
     * 
     * @param composite
     *            a composite widget using this layout
     * @param wHint
     *            width (<code>SWT.DEFAULT</code> for preferred size)
     * @param hHint
     *            height (<code>SWT.DEFAULT</code> for preferred size)
     * @param flushCache
     *            <code>true</code> means flush cached layout values
     * @return a point containing the computed size (width, height)
     * 
     * @see #layout
     * @see Control#getBorderWidth
     * @see Control#getBounds
     * @see Control#getSize
     * @see Control#pack(boolean)
     * @see "computeTrim, getClientArea for controls that implement them"
     */
    protected abstract Point computeSize(Composite composite, int wHint, int hHint, boolean flushCache);
}