Question

所以，我现在正致力于制作一个按键盘命令移动的球。我的问题是，当我调用repaint();时，它会给我一个错误，说明它＆＃34;无法从类型Component中对非静态方法repaint（）进行静态引用。＆＃34;我做错了什么？

import java.awt.*;
import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;
import javax.swing.JFrame;
import javax.swing.SwingUtilities;
import javax.swing.JPanel;
import javax.swing.BorderFactory;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;

public class App extends JFrame{

    JFrame f = new JFrame();
    public static int keyVal = 0, x = 10, y = 10;
    public static void main(String[] args) {
        new App();   
        Ball();
        while(true){
        System.out.println(keyVal);
        try{
            Thread.sleep(50);
        }
        catch(Exception e){}

        }
    }

    public static void Ball(){
        while(true){
            if(keyVal == 65){
            x = x -1;
            }
            else if(keyVal == 68){
            x = x + 1;
            }
        repaint();
        //repaint(x, y, 10, 20);
        }
    }

    public App(){
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.setTitle("Pong");
        f.setSize(30,40);

        f.setLocationRelativeTo(null);

        f.addKeyListener(new KeyListener(){
            public void keyPressed(KeyEvent e){
                keyVal = e.getKeyCode();
            }

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

            public void keyTyped(KeyEvent e){}
        });
        f.add(new MyPanel());
        f.pack();
        f.setVisible(true);
    }

    class MyPanel extends JPanel {
        public MyPanel() {
            setBorder(BorderFactory.createLineBorder(Color.black));
        }

        public Dimension getPreferredSize() {
            return new Dimension(500,200);
        }

        public void paintComponent(Graphics g) {
            super.paintComponent(g);       
            System.out.println("test");
            g.setColor(Color.orange);
            g.fillRect(x, y, 10, 20);
        }  
    }    
}

Answer 1

您的类已经是JFrame子类。无需创建另一个JFrame。取出JFrame f = new JFrame()和所有f.method(..)只需使用method(..)
请勿使用while(true)或Thread.sleep()。你会遇到问题。而是查看How to use a Swing Timer。这是一个简单的example。您还可以找到许多其他示例，只是在如何使用Swing Timer
无需setSize()到框架，您已经pack()了。
您应该查看How to use Key Bindings。如果不是现在，您会发现使用KeyListener时会出现焦点问题。

从Event Dispatch Thead运行您的程序，就像这样

public static void main(String[] args) {
    SwingUtilities.invokeLater(new Runnable(){
        @Override
        public void run() {
            new App();
        }
    });
}

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javax.swing.Timer的简单实现就是这样的

public App() {
    ...
    Timer timer = new Timer(50, new ActionListener(){
        @Override
        public void actionPerformed(ActionEvent e) {
            // do something
        }
    });
}

以下是Timer

Timer( int dalay, ActionListener listener )

延迟每次触发事件时延迟的毫秒数。所以在上面的代码中，每50毫秒会发生一些事情。这将实现您尝试使用Thread.sleep所做的事情。您可以在repaint()

actionPerformed

这是您的代码的简单重构，您可以测试

import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.BorderFactory;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.SwingUtilities;
import javax.swing.Timer;

public class App extends JFrame {

    private MyPanel panel = new MyPanel();
    public static int keyVal = 0, x = 10, y = 10;

    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {
            @Override
            public void run() {
                new App();
            }
        });
    }

    public App() {
        Timer timer = new Timer(50, new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {

                    x = x + 5;

                panel.repaint();
            }
        });
        timer.start();

        add(panel);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setTitle("Pong");
        pack();
        setLocationRelativeTo(null);
        setVisible(true);
    }

    class MyPanel extends JPanel {

        public MyPanel() {
            setBorder(BorderFactory.createLineBorder(Color.black));
        }

        public Dimension getPreferredSize() {
            return new Dimension(500, 200);
        }

        public void paintComponent(Graphics g) {
            super.paintComponent(g);
            System.out.println("test");
            g.setColor(Color.orange);
            g.fillRect(x, y, 10, 20);
        }
    }
}

JFrame repaint（）;错误

1 个答案: