Question

我试图制作一个演示飞船射击游戏。每当我按空格键时，我在Image方法中绘制一个新的抛射物（paintComponent(Graphics g)）并调用moveProjectile()方法。问题是moveProjectile()方法似乎已关闭。

MyJPanel.java

import java.awt.Cursor;
import java.awt.Graphics;
import java.awt.Image;
import java.awt.Point;
import java.awt.Toolkit;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.KeyAdapter;
import java.awt.event.KeyEvent;
import java.awt.event.MouseEvent;
import java.awt.event.MouseMotionListener;
import java.awt.image.BufferedImage;
import java.util.ArrayList;

import javax.swing.ImageIcon;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.Timer;

public class MyJPanel extends JPanel implements ActionListener
{
    private static final long serialVersionUID = 1L;

    private Timer timer;
    private Image backgroundImage;
    private Image player;
    private int playerX, playerY;
    private int projectileX,projectileY;
    private Image projectileImage;
    private ArrayList<Image> projectiles = new ArrayList<Image>();

    boolean flag = false;

    public MyJPanel(Image backgroundImage, Image player,Image projectileImage)
    {
        this.backgroundImage = backgroundImage;
        this.player = player;
        this.projectileImage = projectileImage;
        this.setLayout(null);

        timer = new Timer(50, this);
        timer.start();

        this.addKeyListener(new KeyAdapter() // Listens for a keyboard event
        {
            public void keyPressed(KeyEvent e) 
            {
                if (e.getKeyCode() == KeyEvent.VK_SPACE) // If pressing space - shoot
                {
                    flag = true;
                    moveProjectile();
                }
                repaint();
            }
        });

        // Mouse listener
        this.addMouseMotionListener(new MouseMotionListener()
        {   
            @Override
            public void mouseMoved(MouseEvent e)
            {
                playerX = e.getX();
                playerY = e.getY();
            }

            @Override
            public void mouseDragged(MouseEvent e)
            {

            }
        });
        hideMouseCursor();

        this.setFocusable(true);
        this.setVisible(true);
    } // End of JPanle constructor

    public void paintComponent(Graphics graphics)
    {
        super.paintComponent(graphics);

        graphics.drawImage(backgroundImage,0,0,this.getWidth(),this.getHeight(),null); // Draw the background
        graphics.drawImage(player,playerX,playerY,null); // Draw the player
        if (flag)
        {
            projectileX = playerX + player.getWidth(null);
            projectileY = playerY + player.getHeight(null) / 2 - 27;
            graphics.drawImage(projectileImage,projectileX,projectileY,null);
        }
    }

    public void moveProjectile()
    {
        while (projectileX < this.getWidth())
        {
            this.projectileX += 2;
            repaint();
        }
    }

    public void  hideMouseCursor() // Hides the mouse cursor
    {
        //Transparent 16 x 16 pixel cursor image.
        BufferedImage cursorbackgroundImgage = new BufferedImage(16, 16, BufferedImage.TYPE_INT_ARGB);

        // Create a new blank cursor.
        Cursor blankCursor = Toolkit.getDefaultToolkit().createCustomCursor(
                cursorbackgroundImgage, new Point(0, 0), "Blank Cursor");

        // Set the blank cursor to the JPanel.
        this.setCursor(blankCursor);
    }

    @Override
    public void actionPerformed(ActionEvent actionEvent) // Without the method and the repaint() the mouse listener will not work 
    {
        repaint();
    }

    public class ProjectileThread extends Thread
    {
        @Override
        public void run()
        {
            projectileX = playerX + player.getWidth(null);
            projectileY = playerY + player.getHeight(null) / 2;

        }
    }

    public static void main(String[] args)
    {
        JFrame frame = new JFrame("A Game by me");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setExtendedState(JFrame.MAXIMIZED_BOTH); // Making the frame take a full screen

        ImageIcon backgroundImageIcon = new ImageIcon("space_background_2.jpg");
        Image backgroundImgage = backgroundImageIcon.getImage();
        ImageIcon playerImageIcon = new ImageIcon("spaceship_1.png");
        Image playerImage = playerImageIcon.getImage();
        ImageIcon projectileIcon = new ImageIcon("spaceship_projectile_1.png");
        Image projectileImage = projectileIcon.getImage();  

        frame.add(new MyJPanel(backgroundImgage,playerImage,projectileImage));
        frame.setVisible(true);
    }
} // End of MyJPanel

我不会使用一些变量和方法，所以请不要介意。代码中要注意的要点：

if (e.getKeyCode() == KeyEvent.VK_SPACE) // If pressing space - shoot
{
    flag = true;
    moveProjectile();
}
repaint();

如果按空格 - > flag = true表示

if (flag)
{
    projectileX = playerX + player.getWidth(null);
    projectileY = playerY + player.getHeight(null) / 2 - 27;
    graphics.drawImage(projectileImage,projectileX,projectileY,null);
}

绘制射弹并向右移动。问题是它从未向右移动过。相反，它跟随用鼠标移动的宇宙飞船。

任何建议都将非常感谢。

public class ProjectileThread extends Thread
{
    public ProjectileThread(int playerX,int playerY)
    {
        projectileX = playerX + player.getWidth(null);
        projectileY = playerY + player.getHeight(null) / 2;
    }
    @Override
    public void run()
    {
        while (projectileX < getWidth())
        {
            projectileX += 2;
        }
    }
}



public void keyPressed(KeyEvent e) 
        {
            if (e.getKeyCode() == KeyEvent.VK_SPACE) // If pressing space - shoot
            {
                ProjectileThread projectileThread = new ProjectileThread(playerX,playerY);
                projectileThread.start();
            }
            repaint();
        }

Answer 1

你的moveProjectile方法通过在X坐标上加2来水平移动射弹

this.projectileX += 2;

但是，您的paint方法会使用您的玩家X坐标覆盖此值：

projectileX = playerX + player.getWidth(null);

所以每当你画出你的射弹时，它都与玩家在同一个地方。你需要首先使用玩家坐标绘制射弹，然后移动它而不重置其X坐标。

当发射射弹时，你应该开始一个线程。因此，在空格键的处理程序中，启动线程并将其传递给播放器坐标。这是你的起点。然后在线程的run方法中，移动抛射物并在循环中等待一段时间。

Answer 2

while (projectileX < getWidth())
{
    projectileX += 2;
}

所有这一切都是设置projectile = getWidth（）+ 1（或可能+ 2）。同样，你的moveProjectile方法有：

while (projectileX < this.getWidth())
{
    this.projectileX += 2;
    repaint();
}

同样的事情也是如此。请注意，循环体中的repaint（）基本上什么都不做，因为你阻塞了事件线程，直到moveProjectile（）方法返回

为什么我的射弹（图像对象）没有移动？ Java Swing

2 个答案: