| 法负责计算子组件的大小和位置，并按计算出来的 位置排列子组件。
创建自己的布局类
如果用户希望组件按自己的方式进行布 局，可以创建自己的布局类，实现自己的布局。要实现自己的布局，用户要继承Layout类， 并实现layout方法和computeSize方法。下面将实现一个简单的按列进行布局的布局类，在此 布局中，所有的子组件将按一列显示，并且子组件的宽度相等，代码如例程4所示。
例程4 ColumnLayout.java
public class ColumnLayout extends Layout {
public static final int MARGIN = 4;
public static final int SPACING = 2;
Point [] sizes;
int maxWidth, totalHeight;
protected Point computeSize(Composite composite, int wHint, int hHint,
boolean flushCache) {
Control children[] = composite.getChildren();
if (flushCache || sizes == null || sizes.length != children.length) {
initialize(children);
}
int width = wHint, height = hHint;
if (wHint == SWT.DEFAULT) width = maxWidth;
if (hHint == SWT.DEFAULT) height = totalHeight;
return new Point(width + 2 * MARGIN, height + 2 * MARGIN);
}
protected void layout(Composite composite, boolean flushCache) {
Control children[] = composite.getChildren();
if (flushCache || sizes == null || sizes.length != children.length) {
initialize(children);
}
Rectangle rect = composite.getClientArea();
int x = MARGIN, y = MARGIN;
//计算最大宽度
int width = Math.max(rect.width - 2 * MARGIN, maxWidth);
for (int i = 0; i < children.length; i++) {
int height = sizes[i].y;
//设置子组件 的位置
children[i].setBounds(x, y, width, height);
//计算当前组件的y轴 的坐标
y += height + SPACING;
}
}
void initialize(Control children[]) {
maxWidth = 0;
totalHeight = 0;
sizes = new Point [children.length];
for (int i = 0; i < children.length; i++) {
//计 算子组件的大小
sizes[i] = children[i].computeSize(SWT.DEFAULT, SWT.DEFAULT, true);
maxWidth = Math.max(maxWidth, sizes[i].x);
totalHeight += sizes [i].y;
}
totalHeight += (children.length - 1) * SPACING;
}
}
Eclipse开发经典教程之SWT布局(9)
时间:2011-04-11 阿甘
在ColumnLayout类中，通过layout方法对子组件重新计算位置，并设置子组件的 位置。为了验证ColumnLayout类，下面通过ColumnLayoutTest类测试ColumnLayout类的效果 ，代码如例程5所示。
例程5 ColumnLayoutTest.java
public class ColumnLayoutTest {
static Shell shell;
static Button button3;
public static void main (String[] args) {
Display display = new Display();
shell = new Shell (display);
shell.setLayout(new ColumnLayout());
new Button(shell, SWT.PUSH).setText("B1");
new Button(shell, SWT.PUSH).setText ("Very Wide Button 2");
(button3 = new Button(shell, SWT.PUSH)).setText("Button 3");
new Text(shell, SWT.NONE).setText ("text");
Button grow = new Button(shell, SWT.PUSH);
grow.setText("Grow Button 3");
// 添加选择组件监听器
grow.addSelectionListener(new SelectionAdapter() {
public void widgetSelected(SelectionEvent e) {
button3.setText("Extreemely Wide Button 3");
//组件大小改变后通知父组件进行重新布局
shell.layout ();
shell.pack();
}
});
Button shrink = new Button(shell, SWT.PUSH);
shrink.setText("Shri
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