Eclipse开发经典教程：SWT事件

public class MultipleListenersExample implements HelpListener, VerifyListener,
ModifyListener {
private static final double FIVE_NINTHS = 5.0 / 9.0;
private static final double NINE_FIFTHS = 9.0 / 5.0;
private Text fahrenheit;
private Text celsius;
private Label help;
public void run() {
Display display = new Display();
Shell shell = new Shell(display);
shell.setText("Temperatures");
createContents(shell);
shell.pack();
shell.open();
while (!shell.isDisposed()) {
if (!display.readAndDispatch()) {
display.sleep();
}
}
display.dispose();
}
private void createContents(Shell shell) {
shell.setLayout(new GridLayout(3, true));
new Label(shell, SWT.LEFT).setText("Fahrenheit:");
fahrenheit = new Text(shell, SWT.BORDER);
GridData data = new GridData(GridData.FILL_HORIZONTAL);
data.horizontalSpan = 2;
fahrenheit.setLayoutData(data);
fahrenheit.setData("Type a temperature in Fahrenheit");
// 为华氏温度文本框添加监听器 
fahrenheit.addHelpListener(this);
fahrenheit.addVerifyListener(this);
fahrenheit.addModifyListener(this);
new Label(shell, SWT.LEFT).setText("Celsius:");
celsius = new Text(shell, SWT.BORDER);
data = new GridData(GridData.FILL_HORIZONTAL);
data.horizontalSpan = 2;
celsius.setLayoutData(data);
celsius.setData("Type a temperature in Celsius");
//为摄氏温度文本框添加监听器 
celsius.addHelpListener(this);
celsius.addVerifyListener(this);
celsius.addModifyListener(this);
help = new Label(shell, SWT.LEFT | SWT.BORDER);
data = new GridData(GridData.FILL_HORIZONTAL);
data.horizontalSpan = 3;
help.setLayoutData(data);
}
//响应帮助事件 
public void helpRequested(HelpEvent event) {
help.setText((String) event.widget.getData());
}
　//响应校验事件 
public void verifyText(VerifyEvent event) {
event.doit = false;
char myChar = event.character;
String text = ((Text) event.widget).getText();
if (myChar == '-' && text.length() == 0) event.doit = true;
if (Character.isDigit(myChar)) event.doit = true;
if (myChar == '\b') event.doit = true;
}
　//响应文本修改的事件 
public void modifyText(ModifyEvent event) {
// 删除监听器，从而在modifyText过程中不会触发事件 
celsius.removeVerifyListener(this);
celsius.removeModifyListener(this);
fahrenheit.removeVerifyListener(this);
fahrenheit.removeModifyListener(this);
Text text = (Text) event.widget;
try {
int temp = Integer.parseInt(text.getText());
if (text == fahrenheit) {
celsius.setText(String.valueOf((int) (FIVE_NINTHS * (temp - 32))));
} else {
fahrenheit.setText(String.valueOf((int) (NINE_FIFTHS * temp + 32)));
}
} catch (NumberFormatException e) { /* Ignore */ }
//添加监听器 
celsius.addVerifyListener(this);
celsius.addModifyListener(this);
fahrenheit.addVerifyListener(this);
fahrenheit.addModifyListener(this);
}
public static void main(String[] args) {
new MultipleListenersExample().run();
}
}