ActionPerformed 在自定义组件中不起作用

Question

我正在尝试编写一个代码来创建一个我称之为 gun 的东西，我希望能够将它向右或向左移动。我实现了KeyListener 和ActionListener 方法，但actionPerformed 不起作用。但是，keyPressed 方法确实有效。有什么我错过的想法吗？

public class Gun extends JPanel implements KeyListener, ActionListener {

    /**
     * 
     */
    private static final long serialVersionUID = 1L;
    private static final int GUN_WIDTH = 100;
    private static final int GUN_HEIGHT = 30;
    private static final int GUN_UPPER_HEIGHT = 20;
    private static final int GUN_UPPER_WIDTH = GUN_WIDTH / 4;
    int x, y;
    int velX;

    public Gun() {
        x = 250 - GUN_WIDTH / 2;
        y = 500 - GUN_HEIGHT;
        velX = 0;
        addKeyListener(this);
        setFocusable(true);
        setFocusTraversalKeysEnabled(false);
    }

    @Override
    public void paintComponent(Graphics g) {
        super.paintComponent(g);
        Graphics2D g2d = (Graphics2D) g;

        int upperX = x + GUN_WIDTH / 2 - GUN_UPPER_WIDTH / 2;
        int upperY = y - GUN_UPPER_HEIGHT;

        g2d.setColor(Color.BLACK);
        g2d.fillRect(x, y, GUN_WIDTH, GUN_HEIGHT);
        g2d.fillRect(upperX, upperY, GUN_UPPER_WIDTH, GUN_UPPER_HEIGHT);
    }

    public void left() {
        velX = -1;
    }

    public void right() {
        velX = 1;
    }

    @Override
    public void keyPressed(KeyEvent e) {
        // TODO Auto-generated method stub
        int key = e.getKeyCode();
        if (key == KeyEvent.VK_LEFT) {
            left();
            System.out.println("LEFT");
        }
        if (key == KeyEvent.VK_RIGHT) {
            right();
            System.out.println("RIGHT");
        }
    }

    @Override
    public void keyReleased(KeyEvent arg0) {
    }

    @Override
    public void keyTyped(KeyEvent arg0) {
    }

    @Override
    public void actionPerformed(ActionEvent e) {
        x += velX;
        repaint();
    }

    public static void main(String[] args) {
        Gun gun = new Gun();
        JFrame frame = new JFrame();
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setTitle("Game");
        frame.setLayout(new FlowLayout());

        gun.setPreferredSize(new Dimension(500, 500));

        frame.add(gun);
        frame.setVisible(true);
        frame.pack();
    }

}

Answer 1

要让 actionPerformed 方法运行，您需要为该对象添加一个 ActionListener。由于您没有添加 actionListener，因此您永远不会运行 actionPerformed 方法。

查看有关动作侦听器的 Java 教程：https://docs.oracle.com/javase/tutorial/uiswing/events/actionlistener.html

Answer 2

要运行actionPerformed方法，需要在对应的对象中添加ActionListener。但是 JPanel 类没有名为 addActionListener 的方法。

查看您的代码，您似乎不需要实现 ActionListener 接口。然后你可以摆脱 actionPerformed 方法。您所要做的就是复制 actionPerformed 方法中的代码并将它们粘贴到 keyPressed 方法的 if 条件中。以下是按预期工作的代码：

package edu.uno.ai.planning.bfs;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.FlowLayout;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;

import javax.swing.JFrame;
import javax.swing.JPanel;

public class Gun extends JPanel implements KeyListener{

    /**
     * 
     */
    private static final long serialVersionUID = 1L;
    private static final int GUN_WIDTH = 100;
    private static final int GUN_HEIGHT = 30;
    private static final int GUN_UPPER_HEIGHT = 20;
    private static final int GUN_UPPER_WIDTH = GUN_WIDTH / 4;
    int x, y;
    int velX;

    public Gun() {
        x = 250 - GUN_WIDTH / 2;
        y = 500 - GUN_HEIGHT;
        velX = 0;
        addKeyListener(this);

        setFocusable(true);
        setFocusTraversalKeysEnabled(false);
    }

    @Override
    public void paintComponent(Graphics g) {
        super.paintComponent(g);
        Graphics2D g2d = (Graphics2D) g;

        int upperX = x + GUN_WIDTH / 2 - GUN_UPPER_WIDTH / 2;
        int upperY = y - GUN_UPPER_HEIGHT;

        g2d.setColor(Color.BLACK);
        g2d.fillRect(x, y, GUN_WIDTH, GUN_HEIGHT);
        g2d.fillRect(upperX, upperY, GUN_UPPER_WIDTH, GUN_UPPER_HEIGHT);
    }

    public void left() {
        velX = -1;
    }

    public void right() {
        velX = 1;
    }

    @Override
    public void keyPressed(KeyEvent e) {
        // TODO Auto-generated method stub
        int key = e.getKeyCode();
        if (key == KeyEvent.VK_LEFT) {
            left();
            System.out.println("LEFT");
            x += velX;
            repaint();
        }
        if (key == KeyEvent.VK_RIGHT) {
            right();
            System.out.println("RIGHT");
            x += velX;
            repaint();
        }
    }

    @Override
    public void keyReleased(KeyEvent arg0) {
    }

    @Override
    public void keyTyped(KeyEvent arg0) {
    }

    public static void main(String[] args) {
        Gun gun = new Gun();
        JFrame frame = new JFrame();
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setTitle("Game");
        frame.setLayout(new FlowLayout());

        gun.setPreferredSize(new Dimension(500, 500));

        frame.add(gun);
        frame.setVisible(true);
        frame.pack();
    }

}