Java 游戏需要 mouseDragged 帮助

Question

我正在制作一个简单的 Java 乒乓球游戏，其中有一个球拍和一个球。但是，我成功地在球拍上实现了一个 mouseWheel 来移动。我想改为使用 mouseDragged 事件。我是 Java 新手，这些 mouseEvents 真的很令人困惑。

这是我的球拍课：

import java.awt.Graphics2D;
import java.awt.Rectangle;
import java.awt.event.KeyEvent;
import java.awt.event.MouseEvent;

public class Racquet {
private static final int Y = 330;

private static final int HEIGHT = 10;

int x = 0;
int xa = 0;
static int WIDTH = 60;
private Game game;

public Racquet(Game game) {
    this.game = game;
}

public Racquet(Game game, int WIDTH) {
    this.WIDTH = WIDTH;
}



public void move() {
    if (x + xa > 0 && x + xa < game.getWidth() - WIDTH)
        x = x + xa;
}

public void paint(Graphics2D g) {
    g.fillRect(x, Y, WIDTH, HEIGHT);
}

public void keyReleased(KeyEvent e) {
    xa = 0;
}

public void keyPressed(KeyEvent e) {
    if (e.getKeyCode() == KeyEvent.VK_LEFT)
        xa = -1;
    if (e.getKeyCode() == KeyEvent.VK_RIGHT)
        xa = 1;
}

public Rectangle getBounds() {
    return new Rectangle(x, Y, WIDTH, HEIGHT);
}

public int getTopY() {
    return Y;
}



public void mouseDragged(MouseEvent m) {
    xa = 0;

}
  }

这是我的“游戏”类，我也尝试在其中实现球拍：

import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;
import java.awt.event.MouseEvent;
import java.awt.event.MouseMotionListener;
import java.awt.event.MouseWheelEvent;
import java.io.BufferedReader;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.IOException;
import java.net.MalformedURLException;
import java.util.StringTokenizer;
import java.util.logging.Level;
import java.util.logging.Logger;

import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JOptionPane;
import javax.swing.JPanel;
import javax.swing.JRadioButton;



import javax.swing.ButtonGroup;
import javax.swing.JButton;
addMouseMotionListener(new MouseMotionListener() {

            @Override
            public void mouseDragged(MouseEvent m) {
                    racquet.mouseDragged(m);
            }

            @Override
            public void mouseMoved(MouseEvent arg0) {


            }

Answer 1

基本思想是……

• 当mousePressed 事件发生时，您需要确定该事件是否发生在您的Racquet 中。 Rectangle 有一个简洁的 contains 方法可以做到这一点（这被称为“命中检测”）
• 如果Racquet 被“按下”，则需要计算鼠标事件与Racquet 原点之间的差异（即当前x/y 点）
• 当mouseDragged事件发生时，需要判断Racquet是否真的被拖动了，如果是，则需要计算鼠标点与原点击“偏移量”的差值，这为你提供Racquet 的新起点
• 当mouseReleased 事件发生时，您需要将Racquet 标记为未拖动，因此将来的拖动事件“意外”导致Racquet 被移动

也许是……

MouseAdapter mouseHandler = new MouseAdapter() {

    private Point offset;
    private Racquet racquet;

    @Override
    public void mousePressed(MouseEvent e) {
        // Did we click on a racquet?
        if (racquet.getBounds().contains(e.getPoint())) {
            // The difference between the mouse point and the original of the racquet
            offset = new Point(e.getPoint().x - racquet.getBounds().x, e.getPoint().y - racquet.getBounds().y);
        }
    }

    @Override
    public void mouseDragged(MouseEvent e) {
        // Are we dragging a racquet
        if (offset != null) {
            int newX = e.getPoint().x - offset.x;
            int newY = e.getPoint().y - offset.y;

            // This should be applied as a setting, but here we are
            racquet.x = newX;
        }
    }

    @Override
    public void mouseReleased(MouseEvent e) {
        // Release racquet
        offset = null;
    }

};

// The mouseHandler needs to be added to the primary rendering surface
// component.    
addMouseListener(mouseHandler);
addMouseMotionListener(mouseHander);

旁注：我正在处理一张不完整的图片，并且该解决方案基于类似问题的其他示例。如果您需要更多信息，您需要提供Minimal, Complete, and Verifiable example 以便为问题提供更多背景信息。

不过，我建议阅读以下内容：

• How to Write a Mouse Listener
• How to Write a Mouse-Motion Listener

更好地了解鼠标监听器 API 的工作原理