fillOval() 在 if 语句中不起作用[关闭]

Posted 2023-03-25

【中文标题】fillOval() 在 if 语句中不起作用[关闭]

【英文标题】：fillOval() not working inside a if statement [closed]

【发布时间】：2022-01-22 02:11:56

【问题描述】：

我正在构建一个贪吃蛇游戏，但遇到了问题。我希望只画一次 10 个水果，但我需要更新蛇的位置，所以我添加了一个 if 语句，但 fillOval() 方法不起作用。我通过删除 for 循环和 if 语句对其进行了测试，它工作得很好。代码如下：

import javax.swing.*;
import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

public class SnakeFrame extends JPanel implements ActionListener 

    boolean hasPaintedFruits;

    SnakeFrame()
        JFrame frame = new JFrame("Snake Game");
        frame.setSize(800,600);
        frame.setLocationRelativeTo(null);
        frame.setDefaultCloseOperation(frame.EXIT_ON_CLOSE);
        hasPaintedFruits = false;
        Timer t = new Timer(16, this);
        t.restart();
        frame.add(this);
        frame.setVisible(true);
    

    @Override
    public void paintComponent(Graphics g) 
        super.paintComponent(g);
        if(!hasPaintedFruits) 
            new Fruit().paint(g);
            hasPaintedFruits = true;
        
        new Fruit().paint(g);
        Snake sHead = new Snake();
        sHead.paint(g);
    

    @Override
    public void actionPerformed(ActionEvent e) 
        repaint();
    


import java.awt.*;
import java.util.Random;

public class Fruit 
    //pos
    int x, y;

    Fruit()
        Random random = new Random();
        x = random.nextInt(800);
        y = random.nextInt(600);
    
    public void paint(Graphics g) 
        g.setColor(Color.RED);
        g.fillOval(x,y,10,10);
    

【问题讨论】：

您发布的代码中的 fillOval(...) 调用在哪里？

另外，Fruit 类是扩展 Swing 组件的类吗？如果是这样，您不应该在paint 中创建实例或直接调用paint 方法。

另外，paint 方法不应调用super.paintComponent，因为这会破坏绘制链。它应该调用super.paint。更好的是，你应该覆盖paintComponent，而不是paint。

Fruit 类没有扩展 Swing 组件。让我在这里发布该类的代码

您的绘图方法中似乎有程序逻辑代码，可以更改您的 Swing 组件的状态，这是不明智的。逻辑应该在你的 Swing Timer 中，而绘制方法（应该是 paintComponent 覆盖）应该只根据对象的状态进行绘制，仅此而已。

【参考方案1】：

您的目标是绘制一次，解决方案是摆脱 if 块，并在 paintComponent 方法中简单地绘制需要绘制的内容。例如，假设您有一个带有 x 和 y 位置的 Fruit2 类以及一个 draw 方法：

class Fruit2 
    private static final Color FRUIT_COLOR = Color.BLUE.brighter();
    public static final int FRUIT_SIDE = 20;
    private int x, y;

    public Fruit2(int x, int y) 
        this.x = x;
        this.y = y;
    

    public void draw(Graphics g) 
        g.setColor(FRUIT_COLOR);
        g.fillRect(x, y, FRUIT_SIDE, FRUIT_SIDE);
       

比如说，主绘图类包含一个包含 10 个这些项目的数组：

    private static final int FRUIT_COUNT = 10;
    //.....
    private Fruit2[] fruits = new Fruit2[FRUIT_COUNT];

假设绘图 JPanel 也有一个 Snake2 对象，该对象也有一个 draw 方法（知道如何绘制自己），那么您的 paintComponent 方法将很简单：

    @Override
    protected void paintComponent(Graphics g) 
        super.paintComponent(g);
        for (Fruit2 fruit : fruits) 
            fruit.draw(g);
        
        snake.draw(g);
    

就是这样。 Fruit2 对象自己绘制自己，而蛇自己绘制自己——完成。

同样，正如我在上面的 cmets 中所提到的，绘画方法不应该包含移动蛇的代码 - 将其留给计时器的 ActionListener。相反，绘画方法，这里 paintComponent(...) 只是绘制 GUI 状态的表示，仅此而已。

作为我的意思的一个有效示例，请运行以下代码：

import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.RenderingHints;
import java.awt.geom.Ellipse2D;
import java.awt.geom.Point2D;
import java.util.ArrayList;
import java.util.List;

import javax.swing.*;

public class SnakePanel2 extends JPanel 
    private static final long serialVersionUID = 1L;
    private static final int PANEL_WIDTH = 800;
    private static final int PANEL_HEIGHT = 650;
    private static final int TIMER_DELAY = 40;
    private static final Color BG = Color.WHITE;
    private static final int FRUIT_COUNT = 10;
    private Snake2 snake = new Snake2(PANEL_WIDTH, PANEL_HEIGHT);
    private Fruit2[] fruits = new Fruit2[FRUIT_COUNT];

    public SnakePanel2() 
        setBackground(BG);
        new Timer(TIMER_DELAY, e -> timerStep()).start();
        
        for (int i = 0; i < fruits.length; i++) 
            int x = (int) ((PANEL_WIDTH - Fruit2.FRUIT_SIDE) * Math.random());
            int y = (int) ((PANEL_HEIGHT - Fruit2.FRUIT_SIDE) * Math.random());
            fruits[i] = new Fruit2(x, y);
        
        
    

    private void timerStep() 
        snake.move();
        repaint();
    

    @Override
    protected void paintComponent(Graphics g) 
        super.paintComponent(g);
        for (Fruit2 fruit : fruits) 
            fruit.draw(g);
        
        snake.draw(g);
    
    
    @Override
    public Dimension getPreferredSize() 
        return new Dimension(PANEL_WIDTH, PANEL_HEIGHT);
    

    public static void main(String[] args) 
        SwingUtilities.invokeLater(() -> 
            SnakePanel2 panel = new SnakePanel2();
            JFrame frame = new JFrame("Snake Game");
            frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
            frame.add(panel);
            frame.pack();
            frame.setResizable(false);
            frame.setLocationRelativeTo(null);
            frame.setVisible(true);
        );
    


class Fruit2 
    private static final Color FRUIT_COLOR = Color.BLUE.brighter();
    public static final int FRUIT_SIDE = 20;
    private int x, y;

    public Fruit2(int x, int y) 
        this.x = x;
        this.y = y;
    

    public void draw(Graphics g) 
        g.setColor(FRUIT_COLOR);
        g.fillRect(x, y, FRUIT_SIDE, FRUIT_SIDE);
       


class Snake2 
    private static final int MAX_POINTS = 60;
    private static final int RADIUS = 8;
    private static final int DELTA = 8;
    private static final int DIRECTION_STEPS = 16;
    private static final int DIR_MAX_DELTA = 2;
    private static final Point2D[] DIRECTION_ARRAY = new Point2D[DIRECTION_STEPS];
    private static final Color SNAKE_COLOR = Color.RED;
    private List<Point2D> units = new ArrayList<>();
    private int currentDirection = (DIRECTION_STEPS * 3) / 8;
    private int maxWidth;
    private int maxHeight;
    
    static 
        for (int i = 0; i < DIRECTION_ARRAY.length; i++) 
            double x = DELTA * Math.cos((2 * Math.PI * i) / DIRECTION_ARRAY.length);
            double y = DELTA * Math.sin((2 * Math.PI * i) / DIRECTION_ARRAY.length);
            DIRECTION_ARRAY[i] = new Point2D.Double(x, y);
        
    

    public Snake2(int maxWidth, int maxHeight) 
        this.maxWidth = maxWidth;
        this.maxHeight = maxHeight;
        units.add(new Point2D.Double(0, 0));
    

    public void move() 
        if (units.size() != 1) 
            currentDirection += (2 * DIR_MAX_DELTA + 1) * (Math.random()) - DIR_MAX_DELTA;
            currentDirection += DIRECTION_STEPS;
            currentDirection %= DIRECTION_STEPS; 
        
        
        double x = units.get(0).getX() + DIRECTION_ARRAY[currentDirection].getX();
        double y = units.get(0).getY() + DIRECTION_ARRAY[currentDirection].getY();
        
        if (x < 0) 
            x += maxWidth;
         else if (x > maxWidth) 
            x -= maxWidth;
        
        
        if (y < 0) 
            y += maxHeight;
         else if (y > maxHeight) 
            y -= maxHeight;
        
        
        units.add(0, new Point2D.Double(x, y));
        if (units.size() >= MAX_POINTS) 
            units.remove(units.size() - 1);
        
    

    public void draw(Graphics g) 
        Graphics2D g2 = (Graphics2D) g.create();
        g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
        g2.setColor(SNAKE_COLOR);
        for (Point2D unit : units) 
            double x = unit.getX() - RADIUS;
            double y = unit.getY() - RADIUS;
            double w = 2 * RADIUS;
            double h = w;
            Ellipse2D e2d = new Ellipse2D.Double(x, y, w, h);
            g2.fill(e2d);
        

        g2.dispose();
    

【讨论】：

感谢您的帮助！不幸的是，它仍然没有被绘制一次。每次调用paintComponent() 方法时，都会重新绘制水果