Java：以一定角度移动对象并使用KeyPress改变角度

Question

好的，所以我想要的是矩形始终在移动，但是当您按下左右箭头时，会通过增加或减少角度来改变方向。使用此代码，squaure 会按正确的方向移动，但是当我按下键时，方向不会改变。

import java.awt.*;
import java.awt.Color;
import javax.swing.Timer;
import javax.swing.*;
import java.awt.Graphics;
import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;
import java.awt.event.KeyListener;
import java.awt.event.KeyEvent;
import java.awt.event.KeyAdapter;


public class Fields extends JPanel implements ActionListener, KeyListener{

Timer tm  = new Timer(5, this);
double x = 250, y = 250, vel = 0.2, angle = 90;

public void paintComponent(Graphics g)
{
    super.paintComponent(g);
    this.setBackground(Color.BLACK);
    g.setColor(Color.GREEN);
    g.fillRect((int)x, (int)y, 5, 5);

    tm.start();
}
public void keyTyped(KeyEvent e)
{
    if (e.getKeyCode() == 37) {angle--;}
    if (e.getKeyCode() == 39) {angle++;}
}
public void keyReleased(KeyEvent e)
{
    if (e.getKeyCode() == 37) {angle--;}
    if (e.getKeyCode() == 39) {angle++;}
}
public void keyPressed(KeyEvent e)
{
    if (e.getKeyCode() == 37) {angle--;}
    if (e.getKeyCode() == 39) {angle++;}
}
public void actionPerformed(ActionEvent e)
{

    x += (velX * (float)Math.cos(Math.toRadians(angle - 90)));
    y += (velX * (float)Math.sin(Math.toRadians(angle - 90)));

    repaint();
}
public Fields()
{
    this.addKeyListener(this);
}
public static void main(String[] args)
{
    JFrame f = new JFrame();
    f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    f.setSize(500, 500);
    Fields fi = new Fields();
    f.add(fi);
    f.setVisible(true);

}
}

Answer 1

从我的 cmets 开始...

• 不要在paintComponent 中启动计时器，此方法会被重复调用，并且可以快速连续调用。
• 使用key bindings

.

public class TestAnimation01 {

    public static void main(String[] args) {
        new TestAnimation01();
    }

    public TestAnimation01() {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                    UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                } catch (ClassNotFoundException ex) {
                } catch (InstantiationException ex) {
                } catch (IllegalAccessException ex) {
                } catch (UnsupportedLookAndFeelException ex) {
                }

                JFrame frame = new JFrame();
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.setLayout(new BorderLayout());
                frame.add(new Fields());
                frame.setSize(400, 400);
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }
        });
    }

    public class Fields extends JPanel implements ActionListener {

        Timer tm = new Timer(125, this);
        double x = 250, y = 250, vel = 0.2, angle = 90;
        private int velX = 4;
        private int velY = 4;

        @Override
        public void paintComponent(Graphics g) {
            super.paintComponent(g);
            this.setBackground(Color.BLACK);
            g.setColor(Color.GREEN);
            g.fillRect((int) x, (int) y, 5, 5);
        }

        public void actionPerformed(ActionEvent e) {

            x += (velX * (float) Math.cos(Math.toRadians(angle - 90)));
            y += (velX * (float) Math.sin(Math.toRadians(angle - 90)));

            repaint();
        }

        public Fields() {

            setFocusable(true);

            InputMap im = getInputMap(WHEN_FOCUSED);
            ActionMap am = getActionMap();

            // left 37
            im.put(KeyStroke.getKeyStroke(KeyEvent.VK_LEFT, 0), "goLeft");
            im.put(KeyStroke.getKeyStroke(KeyEvent.VK_RIGHT, 0), "goRight");

            am.put("goLeft", new AbstractAction() {
                @Override
                public void actionPerformed(ActionEvent e) {
                    angle--;
                    repaint();
                }
            });
            am.put("goRight", new AbstractAction() {
                @Override
                public void actionPerformed(ActionEvent e) {
                    angle++;
                    repaint();
                }
            });

            tm.setRepeats(true);
            tm.setCoalesce(true);
            tm.start();

            requestFocusInWindow();

        }
    }
}

还有很多其他的事情你没有涉及，例如边缘条件（当它离开屏幕时会发生什么）和单个 x/y 速度，但我相信你会解决它