java - 学习关键事件

Question

我对java比较陌生，正在尝试学习如何制作一个有这个圆圈的程序，并且我可以使用箭头键移动它。在浏览了一堆例子之后，我能够将一些东西放在一起。虽然我不确定如何创建 KeyEvent。对我所缺少的任何帮助都会很棒。

这就是我到目前为止所拥有的。

    import javax.swing.WindowConstants;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.RenderingHints;
import javax.swing.JFrame;
import javax.swing.JPanel;
import java.awt.Color;
import java.awt.event.KeyEvent;

@SuppressWarnings("serial")
public class Game extends JPanel 
{

    int x = 0;
    int y = 0;
    private void moveBallUP() {
        x = x + 0;
        y = y + 1;       
    }

    private void moveBallDOWN() {
        x = x + 0;
        y = y - 1;       
    }

    private void moveBallLEFT() {
        x = x + 1;
        y = y + 0;       
    }

    private void moveBallRIGHT() {
        x = x - 1;
        y = y + 0;       
    }

    @Override
    public void paint(Graphics g) 
    {
        super.paint(g);
        Graphics2D g2d = (Graphics2D) g;
        g2d.setRenderingHint(RenderingHints.KEY_ANTIALIASING,
            RenderingHints.VALUE_ANTIALIAS_ON);     
            g.setColor(Color.red);
        g2d.fillOval(y, x, 50, 50);
    }

    public static void main(String[] args) throws InterruptedException 
    {
        JFrame frame = new JFrame("Sample Frame");
        Game game = new Game();
        frame.add(game);
        frame.setSize(300, 400);
        frame.setVisible(true);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        if (event.getKeyCode() == KeyEvent.VK_UP) 
        {
            game.moveBallUP();
            game.repaint();
            Thread.sleep(10);
        }

        if (event.getKeyCode() == KeyEvent.VK_DOWN) 
        {
            game.moveBallDOWN();
            game.repaint();
            Thread.sleep(10);
        }

        if (event.getKeyCode() == KeyEvent.VK_LEFT) 
        {
            game.moveBallLEFT();
            game.repaint();
            Thread.sleep(10);
        }

        if (event.getKeyCode() == KeyEvent.VK_RIGHT) 
        {
            game.moveBallRIGHT();
            game.repaint();
            Thread.sleep(10);
        }
    }
}

Answer 1

解决这个问题有几个步骤:首先，使用KeyListener。将以下代码添加到Game类中；这将代表按下了哪些按钮:

private boolean upPressed=false;
private boolean downPressed=false;
private boolean leftPressed=false;
private boolean rightPressed=false;

然后，将其添加到 main 方法中:

frame.addKeyListener(new KeyListener() {
    @Override
    public void keyReleased(KeyEvent event) {
        switch (event.getKeyCode()) {
            case KeyEvent.VK_UP:
                game.upPressed=false;
                break;
            case KeyEvent.VK_DOWN:
                game.downPressed=false;
                break;
            case KeyEvent.VK_LEFT:
                game.leftPressed=false;
                break;
            case KeyEvent.VK_RIGHT:
                game.rightPressed=false;
                break;

        }
    }

    @Override
    public void keyTyped(KeyEvent event) {

    }

    @Override
    public void keyPressed(KeyEvent event) {
        switch (event.getKeyCode()) {
            case KeyEvent.VK_UP:
                game.upPressed=true;
                break;
            case KeyEvent.VK_DOWN:
                game.downPressed=true;
                break;
            case KeyEvent.VK_LEFT:
                game.leftPressed=true;
                break;
            case KeyEvent.VK_RIGHT:
                game.rightPressed=true;
                break;

        }
    }
});

基本上，您将我们创建的变量设置为 true(当按钮按下时)和 false(当按钮释放时)。最后，在 main 方法中添加一个 Timer:

Timer timer = new Timer(10,(e)->{
    if (game.upPressed)
    {
        game.moveBallUP();
        game.repaint();
    }

    if (game.downPressed)
    {
        game.moveBallDOWN();
        game.repaint();
    }

    if (game.leftPressed)
    {
        game.moveBallLEFT();
        game.repaint();
    }

    if (game.rightPressed)
    {
        game.moveBallRIGHT();
        game.repaint();
    }
});
timer.start();

这将每 10 毫秒触发一次，并在按下按钮时调用您的移动方法。

我已经对此进行了测试，并且知道它有效，但是您的移动方法将圆朝错误的方向移动。我想你可以解决这个问题。

编辑:错误在这一行:

g2d.fillOval(y, x, 50, 50);

将其更改为:

g2d.fillOval(x,y , 50, 50);