为什么我的java KeyListener不适用于我的ubuntu？

Question

我正在用java测试我的keyListener。

我的系统在Ubuntu 14.04。我在main中设置一个面板并初始化关键监听器。我还将focusable设置为true，并执行requestFocusInWindow。

但是当我运行该程序时，println从不出现在控制台中。对此感到困惑。

package key; 

import java.awt.Color; 
import java.awt.event.KeyEvent; 
import java.awt.event.KeyListener; 

import javax.swing.JFrame; 
import javax.swing.JPanel; 

public class Key extends JPanel{ 
public void action(){ 
    KeyListener k = new KeyListener(){ 
     @Override 
     public void keyPressed(KeyEvent k){ 
      System.out.println("key is pressed!"); 
     } 
     @Override 
     public void keyReleased(KeyEvent e){ 
      // TODO Auto-generated method stub 
     } 
     @Override 
     public void keyTyped(KeyEvent e){ 
      System.out.println("key is typed!"); 
     } 
    }; 
    this.addKeyListener(k); 
    this.setFocusable(true); 
    this.requestFocusInWindow(); 
} 
public static void main(String[] args){ 
    JFrame frame = new JFrame(); 
    frame.setSize(400,300); 
    JPanel panel = new JPanel(); 
    panel.setBackground(Color.BLUE); 
    frame.add(panel); 
    frame.setVisible(true); 

    Key k = new Key(); 
    k.action(); 
} 
} 

Answer 1

对此有何建议？

• 因为你使用请使用KeyListener
• 的key bindings API添加k到frame它是由可见

例如前...

import java.awt.BorderLayout; 
import java.awt.Color; 
import java.awt.EventQueue; 
import java.awt.event.ActionEvent; 
import java.awt.event.KeyEvent; 
import javax.swing.AbstractAction; 
import javax.swing.ActionMap; 
import javax.swing.InputMap; 
import javax.swing.JFrame; 
import javax.swing.JLabel; 
import javax.swing.JPanel; 
import javax.swing.KeyStroke; 
import javax.swing.UIManager; 
import javax.swing.UnsupportedLookAndFeelException; 

public class Key extends JPanel { 

    public void action() { 
     JLabel label = new JLabel("Waiting"); 
     InputMap inputMap = getInputMap(WHEN_IN_FOCUSED_WINDOW); 
     ActionMap actionMap = getActionMap(); 

     inputMap.put(KeyStroke.getKeyStroke(KeyEvent.VK_A, 0, false), "press.a"); 
     actionMap.put("press.a", new AbstractAction() { 
      @Override 
      public void actionPerformed(ActionEvent e) { 
       label.setText("Pressed A"); 
      } 
     }); 
     inputMap.put(KeyStroke.getKeyStroke(KeyEvent.VK_A, 0, true), "release.a"); 
     actionMap.put("release.a", new AbstractAction() { 
      @Override 
      public void actionPerformed(ActionEvent e) { 
       label.setText("Waiting"); 
      } 
     }); 

     add(label); 
    } 

    public static void main(String[] args) { 
     EventQueue.invokeLater(new Runnable() { 
      @Override 
      public void run() { 
       try { 
        UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName()); 
       } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) { 
        ex.printStackTrace(); 
       } 

       JFrame frame = new JFrame("Testing"); 
       frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); 
       JPanel panel = new JPanel(); 
       panel.setBackground(Color.BLUE); 
       frame.add(panel); 
       Key k = new Key(); 
       k.action(); 
       frame.add(k, BorderLayout.SOUTH); 
       frame.setSize(400, 300); 
       frame.setLocationRelativeTo(null); 
       frame.setVisible(true); 
      } 
     }); 
    } 
}