SWT中模拟AWT的BorderLayout
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。www.ad119.cn/bbs/attachments/basic/20081230/2008123011124145377801.jpg
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 classBorderLayoutextendsLayout {
privateControl north;
privateControl south;
privateControl east;
privateControl west;
privateControl center;
protected voidgetControls(Composite composite) {
Control[] children=composite.getChildren();
for( inti= 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;
}
}
}
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。
protectedPoint computeSize(Composite composite,intwHint,inthHint,
booleanflushCache) {
getControls(composite);
intwidth= 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;
intheightOther=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 newPoint(Math.max(width, wHint), Math.max(height, hHint));
}
computeSize计算Composite所需的大小。
protected voidlayout(Composite composite,booleanflushCache) {
getControls(composite);
Rectangle rect=composite.getClientArea();
intleft=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
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