SWT Listener说明

这次做的项目中用到了SWT包设计界面，在做的过程中有一些widget的常用的事件处理，整理如下：
为一个widget添加Listener,调用 addListener() .其函数原形:
void addListener(int eventType, Listener listener)

eventType为SWT类定义的事件常量 . 每个常量代表程序中的一个事件，比如：SWT.FocusIn，SWT.MouseDoubleClick，SWT.KeyDown等. 常用的事件类型参照表A。第二个参数Listener 对象可以是一个已经定义好有名字的Listener对象，也可以是匿名类，可以是内部类(inner class)也可以是外部类(outer class),不过大多使用匿名的内部类， 例如为一个按钮添加点击事件的监听器，代码如下：

button.addListener(SWT.Selection, new Listener() { 
public void handleEvent(Event e) { 
　　switch (e.type) { 
　　　　　case SWT.Selection: 
　　　　　System.out.println("Button pressed"); 
　　　　  break; 
　　} 
　} 
}); 

Table A: Event Types

Type	Description
SWT.Activate	Triggered when the widget becomes the active window
SWT.Arm	Triggered when the widget is armed
SWT.Close	Triggered when the widget is closed
SWT.Collapse	Triggered when a tree node is collapsed
SWT.Deactivate	Triggered when the widget is no longer the active window
SWT.DefaultSelection	Triggered when the default selection occurs
SWT.Deiconify	Triggered when the widget is restored from being minimized
SWT.Dispose	Triggered when the widget is disposed
SWT.DragDetect	Triggered when the widget is dragged
SWT.Expand	Triggered when a tree node is expanded
SWT.FocusIn	Triggered when the widget gains focus
SWT.FocusOut	Triggered when the widget loses focus
SWT.HardKeyDown	Triggered when a special hardware key, such as on a Pocket PC device, is pressed
SWT.HardKeyUp	Triggered when a special hardware key, such as on a Pocket PC device, is released
SWT.Help	Triggered when the user requests help
SWT.Hide	Triggered when the widget is hidden
SWT.Iconify	Triggered when the widget is minimized
SWT.KeyDown	Triggered when the user presses a key
SWT.KeyUp	Triggered when the user releases a key
SWT.MenuDetect	Triggered when a menu is selected
SWT.Modify	Triggered when the text of a widget is modified
SWT.MouseDoubleClick	Triggered when the mouse is double-clicked
SWT.MouseDown	Triggered when the mouse button is clicked
SWT.MouseEnter	Triggered when the mouse pointer enters the widget
SWT.MouseExit	Triggered when the mouse pointer exits the widget
SWT.MouseHover	Triggered when the mouse pointer hovers over the widget
SWT.MouseMove	Triggered when the mouse pointer moves through the widget
SWT.MouseUp	Triggered when the mouse button is released
SWT.Move	Triggered when the widget is moved
SWT.None	Null event
SWT.Paint	Triggered when the widget is painted
SWT.Resize	Triggered when the widget is resized
SWT.Selection	Triggered when the widget is selected
SWT.Show	Triggered when the widget is shown
SWT.Traverse	Triggered when the user tabs through the controls
SWT.Verify	Triggered when the text for the widget is about to change, allowing you to veto the change

SWT提供了很多事件监听器的接口(Interface)和适配器(Adapter)，可以为控件添加相应的监听器。

为一个文本框添加按键监听器代码形如：

txtSample.addKeyListener(new KeyAdapter() { 
　public void keyPressed(KeyEvent event) { 
　　switch (event.keyCode) { 
　　　　　case SWT.KEYPAD_CR: 
　　　　　case SWT.CR:
　　　　　　　System.out.println("Enter Key be pressed!");
     　　　　　 break; 
　　} 
　} 
}); 

为一个按键添加单击事件监听器，代码形如：

btnSample.addSelectionListener(new SelectionAdapter() { 
　public void widgetSelected(SelectionEvent event) { 
　　//在这里添加按钮单击事件的处理代码
　} 
}); 

给文本框添加文本框内容改变的监听器，代码形如：

txtSample.addModifyListener(new ModifyListener() { 
　public void modifyText(ModifyEvent event) { 
　　//在这里添加文本框文本内容改变的处理代码
　　//一般地，要先移除该文本框的所有监听器以避免不必要的死循环
　　//然后在最后把原来的监听器添加回来
　} 
});

控件的鼠标双击事件也是经常用到的，其添加监听器的代码形如：

shell.addMouseListener(new MouseListener() { 
　public void mouseDoubleClick(MouseEvent event) { 
　　//在这里添加控件双击事件的处理代码　　
　} 
});

另外，当程序中要处理数据输入时，SWT包提供的输入验证监听器非常有用，它可以避免用户的无效数据输入，其添加监听器的代码形如：

/*Called when user types into text box,but before the text box gets what the user typed*/
txtSample.addVerifyListener(new VerifyListener() { 
　public void verifyText(VerifyEvent event) { 

　　//下面是用户输入验证的程序代码示例
　　//Assume you don't allow it
　　event.doit = false;
　　//Get the Character typed
　　char myChar = event.character;
　　//Allow 0~9
　　if ( Character.isDigit(myChar) ) event.doit = true;
　　//Allow Backspace
　　if ( myChar == '/b' ) event.doit = true;
　　else{
　　　　MessageBox msgBox = new MessageBox( shell, SWT.OK | SWT.ICON_ERROR );
　　　　msgBox.setText( "输入错误!" );
　　　　msgBox.setMessage( "你不能输入除数字和退格键以外的字符!" );
　　　　msgBox.open();
　　}　
　} 
}); 

最后再给一个如何处理消息框用户按了哪个键的代码例子：

MessageBox msgBox = new MessageBox( shell, SWT.YES | SWT.NO | SWT.ICON_QUESTION );
msgBox.setText( "消息框的标题" );
msgBox.setMessage( "消息框的提示文字" );
switch( msgBox.open() ){
//msgBox.open()返回所选按钮的常量
　　case SWT.YES:
　　　　　　//程序处理
　　　　　　break;
　　case SWT.NO:
　　　　　　//程序处理
　　　　　　break;
}