無法實現KeyBinding

Question

我試圖移動使用KeyBinding的rectange，但我想我無法正確實施它。 我是一個java初學者，我不能找到這個程序中的錯誤 所以請幫助我。

Thnx提前！

import java.awt.Graphics; 
import java.awt.event.ActionEvent; 
import java.awt.event.ActionListener; 
import javax.swing.AbstractAction; 
import javax.swing.JFrame; 
import javax.swing.JPanel; 
import javax.swing.KeyStroke; 
import javax.swing.SwingUtilities; 
import javax.swing.Timer; 

class Move { 

    public static void main(String args[]) { 
     SwingUtilities.invokeLater(new Runnable() { 
      @Override 
      public void run() { 
       abc(); 
      } 
     }); 
    } 

    private static void abc() { 
     JFrame frame = new JFrame("moving object"); 
     frame.setVisible(true); 
     frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); 
     frame.setSize(1300, 600); 
     frame.add(new P1()); 
    } 
} 

class P1 extends JPanel { 

    int a, b; 
    int x, y; 
    Timer t = new Timer(10, new ActionListener() { 
     @Override 
     public void actionPerformed(ActionEvent e) {//the coordinates of this rectangle 
      a += x;         //are mordified in every 10 millisec 
      b += y;         //x and y changes the direction of the moving 
      repaint();        //rect. 
     } 
    }); 

    P1() { 
     this.getInputMap().put(KeyStroke.getKeyStroke("VK_UP"), "doNothing1"); 
     this.getActionMap().put("doNothing1", new AbstractAction() { 
      @Override 
      public void actionPerformed(ActionEvent e) { 
       x = 0; 
       y = -1; 
      } 
     }); 
     this.getInputMap().put(KeyStroke.getKeyStroke("VK_LEFT"), "doNothing2"); 
     this.getActionMap().put("doNothing2", new AbstractAction() { 
      @Override 
      public void actionPerformed(ActionEvent e) { 
       x = -1; 
       y = 0; 
      } 
     }); 
     this.getInputMap().put(KeyStroke.getKeyStroke("VK_DOWN"), "doNothing3"); 
     this.getActionMap().put("doNothing3", new AbstractAction() { 
      @Override 
      public void actionPerformed(ActionEvent e) { 
       x = 0; 
       y = 1; 
      } 
     }); 
     this.getInputMap().put(KeyStroke.getKeyStroke("VK_RIGHT"), "doNothing4"); 
     this.getActionMap().put("doNothing4", new AbstractAction() { 
      @Override 
      public void actionPerformed(ActionEvent e) { 
       x = -1; 
       y = 0; 
      } 
     }); 
     t.start(); 
     setFocusable(true); 
    } 

    @Override 
    protected void paintComponent(Graphics g) { 
     super.paintComponent(g); 
     g.fillRect(a, b, 10, 10); 
    } 
} 

Answer 1

你正在使用錯誤的InputMap，這是你的問題的一個主要原因。當你沒有指定條件時獲得的默認InputMap使用WHEN_FOCUSED條件，並且由於JPanel默認情況下不允許焦點（並且實際上不應該強制獲得焦點），所以這將不起作用。你反而會想用WHEN_IN_FOCUSED_WINDOW條件。爲此，您必須明確指定。即：

InputMap inputMap = getInputMap(JComponent.WHEN_IN_FOCUSED_WINDOW); // note condition 
inputMap.put(KeyStroke.getKeyStroke("VK_UP"), "doNothing1"); 
// .... 

這甚至會工作，如果綁定組件沒有焦點，只要它是在頂層窗口，確實有重點持有。