SWT中模拟AWT的BorderLayout

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BorderLayout 是 JFrame 的默认布局类，相信大家都用过，SWT没有提供这个Java程序员非常熟悉的Layout类。我们怎们来自己定义一个呢？首先要稍微了解一下Layout的内部实现原理。

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Layouts 是一个容器用来对其子成员布局的一个算法，符合 Strategy Design Pattern . 当 SWT 打开一个 Composite 时，会调用 Composite 里的 layout.computeSize() 计算 Composite 的大小，然后再调 用 layout.layout() 设置子成员的位置和大小 . 如果需要， layout 会调用子成员的 getLayoutData() 来获得单个子成员特别的属性。 computeSize() 和 layout() 是抽象类 Layout 的两个抽象方法。 要定义一个新的 layout ，也就是要定义一个 Layout 的子类， 实现 computeSize 和 layout. 对 BorderLayout 来说，我们需要区分子控件是在哪个位置的 , 是 WEST 的，还是 EAST 的，还是 CENTER 的，这个属性通过 Control.setLayoutData() 方法保存的各个控件里。 废话少说了，先看源代码 public class BorderLayout extends Layout { private Control north; private Control south; private Control east; private Control west; private Control center; protected void getControls(Composite composite) { Control[] children = composite.getChildren(); for ( int i = 0 , n = children.length; i < n; i ) { Control child = children; BorderData borderData = (BorderData) child.getLayoutData(); if (borderData == BorderData.NORTH) north = child; else if (borderData == BorderData.SOUTH) south = child; else if (borderData == BorderData.EAST) east = child; else if (borderData == BorderData.WEST) west = child; else center = child; } } } [1] [2] Control的Layout Data可以用Control.setLayoutData()方法设定, 所以getControl()方法找着各个控件的相应位置。 protected Point computeSize(Composite composite, int wHint, int hHint, boolean flushCache) { getControls(composite); int width = 0 , height = 0 ; width = west == null ? 0 : getSize(west, flushCache).x; width = east == null ? 0 : getSize(east, flushCache).x; width = center == null ? 0 : getSize(center, flushCache).x; if (north != null ) { Point pt = getSize(north, flushCache); width = Math.max(width, pt.x); } if (south != null ) { Point pt = getSize(south, flushCache); width = Math.max(width, pt.x); } height = north == null ? 0 : getSize(north, flushCache).y; height = south == null ? 0 : getSize(south, flushCache).y; int heightOther = center == null ? 0 : getSize(center, flushCache).y; if (west != null ) { Point pt = getSize(west, flushCache); heightOther = Math.max(heightOther, pt.y); } if (east != null ) { Point pt = getSize(east, flushCache); heightOther = Math.max(heightOther, pt.y); } height = heightOther; return new Point(Math.max(width, wHint), Math.max(height, hHint)); } computeSize计算Composite所需的大小。 protected void layout(Composite composite, boolean flushCache) { getControls(composite); Rectangle rect = composite.getClientArea(); int left = rect.x, right = rect.width, top = rect.y, bottom = rect.height; if (north != null ) { Point pt = getSize(north, flushCache); north.setBounds(left, top, rect.width, pt.y); top = pt.y; } if (south != null ) { Point pt = getSize(south, flushCache); south.setBounds(left, rect.height - pt.y, rect.width, pt.y); bottom -= pt.y; } if (east != null ) { Point pt = getSize(east, flushCache); east.setBounds(rect.width - pt.x, top, pt.x, (bottom - top)); right -= pt.x; } if (west != null ) { Point pt = getSize(west, flushCache); west.setBounds(left, top, pt.x, (bottom - top)); left = pt.x; } if (center != null ) { center.setBounds(left, top, (right - left), (bottom - top)); } } 而layout方法让控件们各归其位。整个布局调用是回归的。 完整的代码borderlayout.rar 上一页 [1] [2]