如何在JFrame中使用KeyListener？

Question

因此，我试图用KeyEvent（KeyListener）移动矩形，并且每当我尝试按下键时，矩形都不会移动。

绘制了矩形，但是每当我按left和right键时，都不会发生任何事情。我有两个类，一个是我的带有keyEvents和frame的主类，另一个是绘制矩形并保存用于移动矩形的函数。

这是我的代码：

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

import javax.swing.JFrame;


public class mainFrame extends JFrame implements KeyListener{

mainDraw Draw = new mainDraw();

public void keyPressed(KeyEvent e) {

    int key = e.getKeyCode();

    if(key == KeyEvent.VK_D){

        Draw.moveRight();
    }
}

public void keyReleased(KeyEvent e) {


}
public void keyTyped(KeyEvent e) {}

public mainFrame()
{
    addKeyListener(this);
    setFocusable(true);
    setFocusTraversalKeysEnabled(false);
}

public static void main(String[] args) {

    mainFrame M1 = new mainFrame();

    mainDraw Draw = new mainDraw();

    JFrame frame = new JFrame("Square Move Practice");


    //frame
    frame.setVisible(true);
    frame.setResizable(false);
    frame.setSize(600, 600);
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.getContentPane().add(Draw);

}
}

现在是第二堂课：

import java.awt.Color;
import java.awt.Graphics;

import javax.swing.JComponent;

public class mainDraw extends JComponent{

public int x = 50;
public int y = 50;

public void paint(Graphics g){

    g.drawRect(x, y, 50, 50);
    g.fillRect(x, y, 50, 50);
    g.setColor(Color.BLACK);
}

public void moveRight()
{
    x = x + 5;
    y = y + 0;
    repaint();
}

}

请告诉我如何移动矩形。提前致谢！

Answer 1

矩形没有移动，因为使用不JFrame正确。您必须分配frame给new mainFrame()而不是忽略实例化的mainFrame对象。

@MadProgrammer指出了其他一些问题。

这是修复某些问题的代码：

mainFrame.java

import java.awt.*;
import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;
import javax.swing.JFrame;


public class mainFrame extends JFrame implements KeyListener{
    private mainDraw draw;

    public void keyPressed(KeyEvent e) {
        System.out.println("keyPressed");
    }

    public void keyReleased(KeyEvent e) {
        if(e.getKeyCode()== KeyEvent.VK_RIGHT)
            draw.moveRight();
        else if(e.getKeyCode()== KeyEvent.VK_LEFT)
            draw.moveLeft();
        else if(e.getKeyCode()== KeyEvent.VK_DOWN)
            draw.moveDown();
        else if(e.getKeyCode()== KeyEvent.VK_UP)
            draw.moveUp();

    }
    public void keyTyped(KeyEvent e) {
        System.out.println("keyTyped");
    }

    public mainFrame(){
        this.draw=new mainDraw();
        addKeyListener(this);
        setFocusable(true);
        setFocusTraversalKeysEnabled(false);
    }

    public static void main(String[] args) {
        javax.swing.SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                mainFrame frame = new mainFrame();
                frame.setTitle("Square Move Practice");
                frame.setResizable(false);
                frame.setSize(600, 600);
                frame.setMinimumSize(new Dimension(600, 600));
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.getContentPane().add(frame.draw);
                frame.pack();
                frame.setVisible(true);
            }
        });
    }
}

mainDraw.java

import java.awt.Color;
import java.awt.Graphics;
import javax.swing.JComponent;

public class mainDraw extends JComponent {

    public int x = 50;
    public int y = 50;

    public void paintComponent(Graphics g) {
        super.paintComponent(g);
        g.drawRect(x, y, 50, 50);
        g.fillRect(x, y, 50, 50);
        g.setColor(Color.BLACK);
    }

    public void moveRight() {
        x = x + 5;
        repaint();
    }

    public void moveLeft() {
        x = x - 5;
        repaint();
    }

    public void moveDown() {
        y = y + 5;
        repaint();
    }

    public void moveUp() {
        y = y - 5;
        repaint();
    }
}

顺便说一句，用于SwingUtilities放置gui更新代码，因为swing对象不是线程安全的。