Java中GUI编程讲解（下）

一、事件监听机制

-- 事件源：awt 或swing包中的那些图形界面组件,即发生事件的组件

-- 事件：Event 用户对组件的一个操作

-- 监听器：Listener 负责处理事件的方法

二、java.awt.event 包下的类

WindowEvent //窗口事件,比如用户点了半闭窗口,窗口得到或失去焦点,最大化最小化等

MouseEvent //鼠标事件,鼠标按下,鼠标释放,点击(按下后再松开)等

ActionEvent //动作事件,它不是代表一个具体动作,而是一种语义,比如按纽,或菜单被点击,在文本框中按下回车等,可以这样理解:用户的某一动作导致了某个组件本身的基本作用发生了,这就是ActionEvent事件

不同的事件类型,对应着不同的事件监听器接口,接口的名称和事件的名称是相对应的。

WindowEvent - >WindowListener

MouseEvent ->MouseListener

ActionEvent ->ActionListener

代码示例：

import java.awt.Frame;import java.awt.event.WindowEvent;import java.awt.event.WindowListener;public class Test20 {public static void main(String[] args) {
        Frame f = new Frame();
        f.setSize(400, 400);
        f.setVisible(true);

        f.addWindowListener(new WindowListener() {

            @Overridepublic void windowOpened(WindowEvent e) { // 窗口被打开// TODO Auto-generated method stub}

            @Overridepublic void windowClosing(WindowEvent e) { // 设置关闭事件// TODO Auto-generated method stubSystem.exit(0);
            }

            @Overridepublic void windowClosed(WindowEvent e) { // 用户已经关闭窗口// TODO Auto-generated method stub}

            @Overridepublic void windowIconified(WindowEvent e) { // 被最小化的时候// TODO Auto-generated method stub}

            @Overridepublic void windowDeiconified(WindowEvent e) { // 最小化被还原的时候// TODO Auto-generated method stub}

            @Overridepublic void windowActivated(WindowEvent e) { // 窗体被激活// TODO Auto-generated method stub}

            @Overridepublic void windowDeactivated(WindowEvent e) { // 失去焦点的时候// TODO Auto-generated method stub}

        });
    }
}

有没有发现，用WindowListener接口的时候，会引入一大堆不常用的代码（这里我们只想设置关闭），借口里的方法只能被覆盖，又不能删掉，这样就是的整个项目显得很罗嗦，为了解决这个事情，就有了事件适配器。

三、事件适配器

JDK 针对大多数事件监听器接口类定义了相应的实现类（里面有很多空实现的方法，方便我们创建侦听器对象），我们称为事件适配器类。这里我用到了WindowAdapter。

import java.awt.Frame;import java.awt.event.WindowAdapter;import java.awt.event.WindowEvent;public class Test21 {public static void main(String[] args) {
        Frame f = new Frame("事件适配器的栗子");
        f.setSize(400, 400);
        f.setVisible(true);

        f.addWindowListener(new WindowAdapter() {public void windowClosing(WindowEvent e) {
                System.exit(0);
            }
        });
    }
}

可以观察一下WindowAdapter类的源码，找找感觉。

public abstract class WindowAdapterimplements WindowListener, WindowStateListener, WindowFocusListener
{/** * Invoked when a window has been opened.     */public void windowOpened(WindowEvent e) {}/** * Invoked when a window is in the process of being closed.
     * The close operation can be overridden at this point.     */public void windowClosing(WindowEvent e) {}/** * Invoked when a window has been closed.     */public void windowClosed(WindowEvent e) {}/** * Invoked when a window is iconified.     */public void windowIconified(WindowEvent e) {}/** * Invoked when a window is de-iconified.     */public void windowDeiconified(WindowEvent e) {}/** * Invoked when a window is activated.     */public void windowActivated(WindowEvent e) {}/** * Invoked when a window is de-activated.     */public void windowDeactivated(WindowEvent e) {}/** * Invoked when a window state is changed.
     * @since 1.4     */public void windowStateChanged(WindowEvent e) {}/** * Invoked when the Window is set to be the focused Window, which means
     * that the Window, or one of its subcomponents, will receive keyboard
     * events.
     *
     * @since 1.4     */public void windowGainedFocus(WindowEvent e) {}/** * Invoked when the Window is no longer the focused Window, which means
     * that keyboard events will no longer be delivered to the Window or any of
     * its subcomponents.
     *
     * @since 1.4     */public void windowLostFocus(WindowEvent e) {}
}

练习几个个事件处理程序的栗子吧。

例一：

import java.awt.Button;import java.awt.FlowLayout;import java.awt.Frame;import java.awt.event.ActionEvent;import java.awt.event.ActionListener;//例一：在窗体中放置一个按纽,点击后让程序退出class TestFrame implements ActionListener { // ActionListener接口里面只有一个方法，下面会重写private Frame f;public TestFrame() {
        f = new Frame("窗口");
        init();
    }private void init() {
        f.setSize(300, 300);
        f.setLayout(new FlowLayout());// 布局模式Button b = new Button("退出程序");
        b.addActionListener(this);
        f.add(b);
        f.setVisible(true);

    }

    @Overridepublic void actionPerformed(ActionEvent e) {// TODO Auto-generated method stubf.setVisible(false);
        f.dispose();// 在关闭的时候，可以用它来销毁窗体资源System.exit(0);// 退出    }

}public class Test22 {public static void main(String[] args) {new TestFrame();
    }

}

上面的，点击退出程序按钮才可以退出，点击右上角的X，是不可以退出的哦。因为没有设置WindowListener哦。

这个例子用到ActionListener接口，可以看一下它的源代码，如下：

public interface ActionListener extends EventListener {/** * Invoked when an action occurs.     */public void actionPerformed(ActionEvent e);

}

例二：

  TextField txtNo;=  Frame("请输入密码"f.setBounds(50, 50, 400, 400);f.setLayout( FlowLayout());=  TextField(10);  code = (!(code >= KeyEvent.VK_0 && code <= KeyEvent.VK_9)) {System.out.println(KeyEvent.getKeyText(code) + "输入有误" 0

测试类：

public class Test23 {public static void main(String[] args) {new TestFrame();
    }
}

例三：

列出指定目录的内容：

import java.awt.Button;import java.awt.FlowLayout;import java.awt.Frame;import java.awt.TextArea;import java.awt.TextField;import java.awt.event.ActionEvent;import java.awt.event.ActionListener;import java.awt.event.WindowAdapter;import java.awt.event.WindowEvent;import java.io.File;public class Test24 {public static void main(String[] args) {new MyWindow();
    }
}class MyWindow {
    MyWindow() {
        init();
    }private Frame f;private Button b;private TextField txtDir;// 用来输入目录名称private TextArea txtFileList;// 用来显示文件列表private void init() {
        f = new Frame("窗口");
        f.setBounds(44, 44, 500, 500);
        f.setLayout(new FlowLayout());

        txtDir = new TextField(8);
        b = new Button("显示");
        txtFileList = new TextArea(20, 30);// 用来显示文件列表的区域f.add(txtDir);
        f.add(b);
        f.add(txtFileList);
        initEvent();
        f.setVisible(true);
    }private void initEvent() {// TODO Auto-generated method stubf.addWindowListener(new WindowAdapter() {/** * Invoked when a window is in the process of being closed. The
             * close operation can be overridden at this point.             */public void windowClosing(WindowEvent e) {
                System.exit(0);
            }
        });
        b.addActionListener(new ActionListener() {/** * Invoked when an action occurs.             */public void actionPerformed(ActionEvent e) {
                txtFileList.setText("");
                String dirStr = txtDir.getText();// 取出用户输入的路径File file = new File(dirStr);if (file.isDirectory() && file.exists()) {
                    String[] fileNameList = file.list();for (String s : fileNameList) {
                        txtFileList.append(s + "\r\n");// 别忘了换行符                    }
                } else {
                    txtFileList.append("输入有误，请重新输入");
                }
            }
        });

    }
}

结果：（我让它显示我D盘的目录）

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