001: /*******************************************************************************
002: * Copyright (c) 2000, 2005 IBM Corporation and others.
003: * All rights reserved. This program and the accompanying materials
004: * are made available under the terms of the Eclipse Public License v1.0
005: * which accompanies this distribution, and is available at
006: * http://www.eclipse.org/legal/epl-v10.html
007: *
008: * Contributors:
009: * IBM Corporation - initial API and implementation
010: *******************************************************************************/package org.eclipse.swt.widgets;
011:
012: import org.eclipse.swt.graphics.*;
013:
014: /**
015: * A layout controls the position and size
016: * of the children of a composite widget.
017: * This class is the abstract base class for
018: * layouts.
019: *
020: * @see Composite#setLayout(Layout)
021: */
022: public abstract class Layout {
023:
024: /**
025: * Computes and returns the size of the specified
026: * composite's client area according to this layout.
027: * <p>
028: * This method computes the size that the client area
029: * of the composite must be in order to position all
030: * children at their preferred size inside the
031: * composite according to the layout algorithm
032: * encoded by this layout.
033: * </p>
034: * <p>
035: * When a width or height hint is supplied, it is
036: * used to constrain the result. For example, if a
037: * width hint is provided that is less than the
038: * width of the client area, the layout may choose
039: * to wrap and increase height, clip, overlap, or
040: * otherwise constrain the children.
041: * </p>
042: *
043: * @param composite a composite widget using this layout
044: * @param wHint width (<code>SWT.DEFAULT</code> for preferred size)
045: * @param hHint height (<code>SWT.DEFAULT</code> for preferred size)
046: * @param flushCache <code>true</code> means flush cached layout values
047: * @return a point containing the computed size (width, height)
048: *
049: * @see #layout
050: * @see Control#getBorderWidth
051: * @see Control#getBounds
052: * @see Control#getSize
053: * @see Control#pack(boolean)
054: * @see "computeTrim, getClientArea for controls that implement them"
055: */
056: protected abstract Point computeSize(Composite composite,
057: int wHint, int hHint, boolean flushCache);
058:
059: /**
060: * Instruct the layout to flush any cached values
061: * associated with the control specified in the argument
062: * <code>control</code>.
063: *
064: * @param control a control managed by this layout
065: * @return true if the Layout has flushed all cached information associated with control
066: *
067: * @since 3.1
068: */
069: protected boolean flushCache(Control control) {
070: return false;
071: }
072:
073: /**
074: * Lays out the children of the specified composite
075: * according to this layout.
076: * <p>
077: * This method positions and sizes the children of a
078: * composite using the layout algorithm encoded by this
079: * layout. Children of the composite are positioned in
080: * the client area of the composite. The position of
081: * the composite is not altered by this method.
082: * </p>
083: * <p>
084: * When the flush cache hint is true, the layout is
085: * instructed to flush any cached values associated
086: * with the children. Typically, a layout will cache
087: * the preferred sizes of the children to avoid the
088: * expense of computing these values each time the
089: * widget is laid out.
090: * </p>
091: * <p>
092: * When layout is triggered explicitly by the programmer
093: * the flush cache hint is true. When layout is triggered
094: * by a resize, either caused by the programmer or by the
095: * user, the hint is false.
096: * </p>
097: *
098: * @param composite a composite widget using this layout
099: * @param flushCache <code>true</code> means flush cached layout values
100: */
101: protected abstract void layout(Composite composite,
102: boolean flushCache);
103: }
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