使用KeyListener在JPanel中使用箭头键移动矩形

问题描述：

我一直在尝试使用箭头键移动JPanel.它没有工作.我相信是扩展KeyAdapter的内部类.我也不确定是否实现了ActionListener.我参加的其他课程并不重要，因为它只是框架.

I have been trying to make a JPanel move with the arrow keys. It has not been working. I believe it is my inner class that extends the KeyAdapter. I'm also not sure about the ActionListener implemented were it is. The other class I have made does not matter since it is just the frame.

package jerryWorlds;

import javax.swing.*;
import java.awt.*;
import java.awt.event.*;

public class Jerry extends JPanel implements ActionListener{

int SizeX, SizeY, PosX, PosY, VelX, VelY;
Image img;
Timer time = new Timer(1, this);

public Jerry(){
    ImageIcon i = new ImageIcon();
    addKeyListener(new AL());
    time.start();
    img = i.getImage();
    PosX = 375;
    PosY = 250;
}

public void paint(Graphics g){
    Graphics2D g2d = (Graphics2D)g;
    g2d.fillRect(PosX, PosY, 50, 100);
}
public void actionPerformed(ActionEvent e) {
    PosX = PosX + VelX;
    repaint();
}

private class AL extends KeyAdapter{
    public void keyPressed(KeyEvent e) {
        int key = e.getKeyCode();
        System.out.println("YAY!");
        if(key == KeyEvent.VK_LEFT)
            VelX = -1;
        else if(key == KeyEvent.VK_RIGHT)
            VelX = 1;
    }

    public void keyReleased(KeyEvent e) {
        int key = e.getKeyCode();
        if(key == KeyEvent.VK_LEFT)
            VelX = 0;
        else if(key == KeyEvent.VK_RIGHT)
            VelX = 0;
    }
}

}

答

您将要在本网站上搜索类似的问题，因为它们通常具有相同的问题和相同的答案.
他们会告诉您焦点是一个问题，因为组件的KeyListener除非有焦点，否则将无法工作.
他们会告诉您，无论您什么时候都不要使用KeyListener，而应该只使用Key Bindings.
除非您确定要覆盖组件的边框和子对象的绘画(不要)，否则它们会告诉您不要覆盖paint(...)而是覆盖paintComponent(...).
他们会告诉您确保在paintComponent(...)内部调用super方法.

You will want to search this site for similar questions, as they usually have the same issue and same answer.
They will tell you that focus is one problem since a component's KeyListener won't work unless it has focus.
They will tell you that regardless you shouldn't use KeyListener at all but rather Key Bindings.
They will tell you not to override paint(...) but rather paintComponent(...) unless you are sure that you want to override painting of a component's borders and children (you don't).
They will tell you to be sure to call the super method inside of paintComponent(...).

还请查看此动画和键绑定示例.

使用KeyListener在JPanel中使用箭头键移动矩形

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