Java - KeyListener事件不触发

Question

我已经开始用java写一个简单的平台游戏。作为测试，我编写了这个简单的程序，当您按下箭头键时，它会在applet周围移动一个矩形。关键事件根本没有触发。代码如下：

import java.applet.*;
import java.awt.*;
import java.awt.event.*;
public class Game extends Applet implements Runnable, KeyListener
{
  //setup data
  Thread t;
  Image buffimg;
  Graphics draw;
  Dimension dim;

  //game variables
  int charx = 400;//rectangles X and Y positions
  int chary = 50;
  boolean leftArrow = false;
  public void init()
  {
        setSize(800, 500);
        t = new Thread(this);
        t.start();
       addKeyListener( this );
  }
  public void run()
  {
        while(true)
        {
          repaint();
          moveChar();//move the rectangle
          try {
                t.sleep(1000/30);
          } catch (InterruptedException e) { ; }
        }
  }
   public void keyPressed( KeyEvent e ) 
   { 
       int k = e.getKeyCode();
       if(k == 37)
       {
           leftArrow = true;
           charx--;
       }

   }
   public void keyReleased( KeyEvent e ) 
   { 
       if(e.getKeyCode() == 37)
       {
           leftArrow = false;
       }
   }
   public void keyTyped( KeyEvent e ) 
   {
   }
  public void moveChar()
  {
      //move rectangle on left arrow key press
      if(leftArrow == true)
      {
          charx--;
      }  
  }
  public void paint(Graphics g)
  {
      g.drawRect(charx, chary, 100, 100);
  }
  public void update (Graphics g)
  {
      //double buffering

      // initialize buffer
      if (buffimg == null)
      {
          buffimg = createImage (this.getSize().width, this.getSize().height);
          draw = buffimg.getGraphics ();
      }
      // clear screen in background
      draw.setColor (getBackground ());
      draw.fillRect (0, 0, this.getSize().width, this.getSize().height);
      // draw elements in background
      draw.setColor (getForeground());
      paint (draw);
      // draw image on the screen
      g.drawImage (buffimg, 0, 0, this);
  } 
}

为什么他们不开火，我该如何解决这个问题？

Answer 1

this.requestFocusInWindow(); // end of init(), or better, in start()

Answer 2

我试过你的代码了。它按其应有的方式工作。

问题是，您需要先在绘图区域上按下鼠标以使其成为焦点，然后它才能接收事件。

要自动执行此操作，请使用以下命令: requestFocusInWindow()