常见监听器的使用

监听器的使用

• ActionListener：监听按钮，菜单，复选框，单选框都可以
• MouseListener：监听窗体 面板
• MouseMotionListener：监听窗体，面板
• KeyListener：监听窗体
• ChangeListener：滑杆

监听器的原理

• 所有的监听器都是接口 interface
  所有的接口的必须条件，必须重写接口中的所有抽象方法
  接口实现：一个类可以实现多个接口
• Adapter类：实现了相关的所有接口，并重写了所有的方法，但是没有添加内容，也可以通过继承Adapter类来实现监听器
  继承：
  不强制重写方法，可以选择性重写方法
  一个类只能直接继承一个父类

实例代码

• 适配器

public class MyAdapter implements MouseListener, ActionListener,MouseMotionListener, KeyListener, ChangeListener {
    @Override
    public void actionPerformed(ActionEvent e) {

    }

    @Override
    public void keyTyped(KeyEvent e) {

    }

    @Override
    public void keyPressed(KeyEvent e) {

    }

    @Override
    public void keyReleased(KeyEvent e) {

    }

    @Override
    public void mouseClicked(MouseEvent e) {

    }

    @Override
    public void mousePressed(MouseEvent e) {

    }

    @Override
    public void mouseReleased(MouseEvent e) {

    }

    @Override
    public void mouseEntered(MouseEvent e) {

    }

    @Override
    public void mouseExited(MouseEvent e) {

    }

    @Override
    public void stateChanged(ChangeEvent e) {

    }

    @Override
    public void mouseDragged(MouseEvent e) {

    }

    @Override
    public void mouseMoved(MouseEvent e) {

    }
}

• 功能实现类

public class UIListener extends MyAdapter{
    public JLabel jslValue;
    @Override
    public void mouseClicked(MouseEvent e) {
        System.out.println("鼠标监听器，按下");
    }

    @Override
    public void keyPressed(KeyEvent e) {
        System.out.println("键盘监听器："+e.getKeyChar());
    }

    @Override
    public void mouseDragged(MouseEvent e) {
        System.out.println("鼠标拖动监听器："+e.getX());
    }

    @Override
    public void actionPerformed(ActionEvent e) {
        System.out.println("动作监听器："+e.getActionCommand());
        String ac = e.getActionCommand();
        if (ac.equals("打开")){
            //可以指向用户目录
            JFileChooser chooser = new JFileChooser();
            FileNameExtensionFilter filter = new FileNameExtensionFilter(
                    "JPG & GIF Images", "jpg", "gif");
            chooser. setFileFilter(filter);
            int returnVal = chooser. showOpenDialog(null);
            if(returnVal == JFileChooser. APPROVE_OPTION) {
                File file = chooser.getSelectedFile();
                System. out. println("You chose to open this file: " +
                        file.getParentFile());
            }else {
                System.out.println("取消操作");
            }

        }
    }

    @Override
    public void stateChanged(ChangeEvent e) {
//        System.out.println("状态改变监听器："+e.getSource());
        //获取滑杆的值
        JSlider source = (JSlider) e.getSource();
        System.out.println("状态改变监听器:"+source.getValue());
        //获取标签值
        jslValue.setText(source.getValue()+"");
    }
}

• 面板类

public class UI extends JFrame {
    UIListener ul = new UIListener();
    public UI() {
        this.setTitle("监听器");
        this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        this.setSize(800, 800);
        this.setLocationRelativeTo(null);
        //设置流式布局
        this.setLayout(new FlowLayout());
        //设置菜单栏
        JMenuBar menuBar = new JMenuBar();
        String[] menuStr = {"File","Edit","View","Navigate"};
        String[] menItmStr = {"1","2","3","4","5","6"};
        for (int i = 0; i < menuStr.length; i++) {
            JMenu menu = new JMenu(menuStr[i]);
            for (int j = 0; j < menItmStr.length; j++) {
                JMenuItem menuItem = new JMenuItem(menuStr[i]+menItmStr[j]);
                menu.add(menuItem);
                menuItem.addActionListener(ul);
            }
            menuBar.add(menu);
        }
        //添加按钮
        this.setJMenuBar(menuBar);
        JButton btn = new JButton("打开");
        this.add(btn);
        btn.addActionListener(ul);
        //设置滑杆
        JSlider jSlider = new JSlider(SwingConstants.VERTICAL);
        this.add(jSlider);
        jSlider.addChangeListener(ul);
        JLabel islValue = new JLabel(0 + "");
        this.add(islValue);
        ul.jslValue = islValue;


        this.setVisible(true);
        //请求焦点到窗体
        this.requestFocusInWindow();
    }

    public static void main(String[] args) {
        new UI();
    }
}