为什么我不能向 JPanel 添加多个对象？

Question

当我向 GameScreen 添加多个对象时 class Duck 只有一个出现在屏幕上。当我在 GameScreen class 中添加 Duck 外部构造函数时，我有很多 Duck 对象，但是 mouseClicked 方法在 Duck 上不起作用。

Answer 1

看看How to Use BorderLayout。 BorderLayout 将只显示添加到任何单个位置的最后一个组件。

话虽如此，我认为这不是您真正想要进入的方向。相反，从单个 JPanel 开始并覆盖其 paintComponent 方法，然后渲染所有您游戏对象直接通过。组件是非常复杂的重物，通常不适合这种操作。

此外，您也不需要 3 个以上的线程（Swing Timer 使用一个线程来安排对 UI 的调用）。使用单个 Swing Timer 作为您的“主游戏循环”，它应该负责更新状态和安排绘制通道。 Swing 不是线程安全的，因此不建议使用 Thread 更新标签。

import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Rectangle;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.image.BufferedImage;
import java.awt.image.ImageObserver;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
import java.util.Random;
import javax.imageio.ImageIO;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.Timer;

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

    public Main() {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                    BufferedImage img = ImageIO.read(getClass().getResource("/images/Duck.png"));
                    List<Duck> ducks = new ArrayList<>();
                    ducks.add(new Duck(img));
                    ducks.add(new Duck(img));

                    JFrame frame = new JFrame();
                    frame.add(new GamePane(ducks));
                    frame.pack();
                    frame.setLocationRelativeTo(null);
                    frame.setVisible(true);
                } catch (IOException ex) {
                    ex.printStackTrace();
                }
            }
        });
    }

    public class Duck {
        private BufferedImage image;

        private int x;
        private int y;

        private int xDelta = 0;
        private int yDelta = 0;

        public Duck(BufferedImage image) {
            this.image = image;
        }

        public BufferedImage getImage() {
            return image;
        }

        public int getX() {
            return x;
        }

        public int getY() {
            return y;
        }

        public void setLocation(int x, int y) {
            setX(x);
            setY(y);
        }

        public void setX(int x) {
            this.x = x;
        }

        public void setY(int y) {
            this.y = y;
        }

        public int getWidth() {
            return image == null ? 0 : image.getWidth();
        }

        public int getHeight() {
            return image == null ? 0 : image.getHeight();
        }

        public void setDelta(int x, int y) {
            xDelta = x;
            yDelta = y;
        }

        public int getXDelta() {
            return xDelta;
        }

        public int getYDelta() {
            return yDelta;
        }

        public void move(Rectangle bounds) {
            int xDelta = getXDelta();
            int yDelta = getYDelta();
            int x = getX() + xDelta;
            int y = getY() + yDelta;

            if (x < bounds.x) {
                x = bounds.x;
                xDelta *= -1;
            } else if (x + getWidth() >= bounds.x + bounds.width) {
                x = (bounds.x + bounds.width) - getWidth();
                xDelta *= -1;
            }

            if (y < bounds.y) {
                y = bounds.y;
                yDelta *= -1;
            } else if (y + getWidth() >= bounds.y + bounds.height) {
                y = (bounds.y + bounds.height) - getHeight();
                yDelta *= -1;
            }
            setDelta(xDelta, yDelta);
            setLocation(x, y);
        }

        public void paint(Graphics2D g2d, ImageObserver observer) {
            g2d.drawImage(getImage(), getX(), getY(), observer);
        }
    }

    public class GamePane extends JPanel {
        private List<Duck> ducks;

        public GamePane(List<Duck> ducks) {
            this.ducks = ducks;

            Random rnd = new Random();

            for (Duck duck : ducks) {
                int width = 400 - duck.getWidth();
                int height = 400 - duck.getHeight();

                int x = rnd.nextInt(width);
                int y = rnd.nextInt(height);

                int xDelta = rnd.nextBoolean() ? 1 : -1;
                int yDelta = rnd.nextBoolean() ? 1 : -1;

                duck.setLocation(x, y);
                duck.setDelta(xDelta, yDelta);
            }

            Timer timer = new Timer(5, new ActionListener() {
                @Override
                public void actionPerformed(ActionEvent e) {
                    Rectangle bounds = new Rectangle(getSize());
                    for (Duck duck : ducks) {
                        duck.move(bounds);
                    }
                    repaint();
                }
            });
            timer.start();
        }

        @Override
        public Dimension getPreferredSize() {
            return new Dimension(400, 400);
        }

        @Override
        protected void paintComponent(Graphics g) {
            super.paintComponent(g);
            for (Duck duck : ducks) {
                Graphics2D g2d = (Graphics2D) g.create();
                duck.paint(g2d, this);
                g2d.dispose();
            }
        }
    }
}

由此，您可以根据需要开始添加更多实体，例如，我可以修改 Main 方法以包含很多鸭子...

BufferedImage img = ImageIO.read(getClass().getResource("/images/Duck.png"));
List<Duck> ducks = new ArrayList<>(100);
for (int index = 0; index < 100; index++) {
    ducks.add(new Duck(img));
}

这显然是一个过于简化的示例，仅用于演示核心概念，您需要对基本游戏开发和 2D 图形进行更多研究。

为什么我不能向 JPanel 添加多个对象？

Why I can't add more than one Object to the JPanel?

java

swing

jpanel

paintcomponent