JPanel不响应keylistener

问题描述

我试图制作一个JPanel，该面板可以显示您按下每个导航键的次数，但它只显示4个零.

I tried to make a JPanel that would display how many times you press each navigation key, but it is only displaying 4 zeros.

///在keyPressed()方法中，我放置了以下代码来相应地处理按键:

//In the keyPressed() method, I put the following code that handles key presses accordingly:

public void keyPressed(KeyEvent event)
{
    if(event.getKeyCode()==KeyEvent.VK_LEFT)
    left++;
    else if(event.getKeyCode()==KeyEvent.VK_RIGHT)
    right++;
    else if(event.getKeyCode()==KeyEvent.VK_UP)
    up++;
    else if(event.getKeyCode()==KeyEvent.VK_DOWN)
    down++;
}

//通过paint方法在JPanel上绘制计数

//the paint method to paint the counts over JPanel

public void paintComponent(Graphics g)
{
    super.paintComponent(g);
    g.drawString ( Integer.toString(left),   100, 100 );
    g.drawString ( Integer.toString(right),  200, 100 );
    g.drawString ( Integer.toString(up),     100, 200 );
    g.drawString ( Integer.toString(down),   200, 200 );
}

推荐答案

• 最后在keyPressed()方法中调用repaint();.

  • Call repaint(); in keyPressed() method in the end.

    在创建后的main方法中调用count_keys.setFocusable(true);

    Call count_keys.setFocusable(true); in main method just below its creation

    由于JPanel无法对焦，因此KeyListener无法正常工作.

    Because JPanel is not focus able hence KeyListener is not working.

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