/******************************************************************************* * 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 Sample code and further information */ public abstract class Layout { /** * Computes and returns the size of the specified * composite's client area according to this layout. *
* 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. *
** 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. *
* * @param composite a composite widget using this layout * @param wHint width (SWT.DEFAULT
for preferred size)
* @param hHint height (SWT.DEFAULT
for preferred size)
* @param flushCache true
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
* control
.
*
* @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.
* * 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. *
** 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. *
** 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. *
* * @param composite a composite widget using this layout * @param flushCachetrue
means flush cached layout values
*/
protected abstract void layout (Composite composite, boolean flushCache);
}