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/*******************************************************************************
* Copyright (c) 2000, 2011 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.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 flushCache true means flush cached layout values
*/
protected abstract void layout (Composite composite, boolean flushCache);
}