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

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

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/*******************************************************************************
 * Copyright (c) 2000, 2011 IBM Corporation and others.
 *
 * This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License 2.0
 * which accompanies this distribution, and is available at
 * https://www.eclipse.org/legal/epl-2.0/
 *
 * SPDX-License-Identifier: EPL-2.0
 *
 * Contributors:
 *     IBM Corporation - initial API and implementation
 *******************************************************************************/
package org.eclipse.swt.widgets;

import org.eclipse.swt.graphics.*;

/**
 * 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)
 * @see <a href="http://www.eclipse.org/swt/">Sample code and further information</a>
 */
public abstract class Layout {

    /**
     * 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);

    /**
     * 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
     *
     * @since 3.1
     */
    protected boolean flushCache(Control control) {
        return false;
    }

    /**
     * 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);
}