java - 为什么我的图标不会重新绘制？

Question

这是我的主要类(class):

package fast;

import java.awt.BorderLayout;
import java.awt.Color;
import java.io.IOException;
import javax.swing.JFrame;
import javax.swing.JPanel;

public class Fast {

    public JFrame frame = new JFrame("Fast");
    public JPanel panel = new JPanel();
    public Screen screen = new Screen();

    public Fast() throws IOException {
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setSize(1000, 500);
        frame.setVisible(true);
        frame.setLocationRelativeTo(null);
        frame.setLayout(new BorderLayout());
        frame.setBackground(Color.YELLOW);
        frame.add(screen);
        screen.setBackground(Color.WHITE);
    }
    public static void main(String[] args) throws IOException {
        Fast f = new Fast();
        Thread thread = new Thread(new Screen());
        thread.start();
    }
}

这是我的屏幕类:

package fast;

import java.awt.Color;
import java.awt.Graphics;
import java.awt.image.BufferedImage;
import java.io.File;
import java.io.IOException;
import javax.imageio.ImageIO;
import javax.swing.ImageIcon;
import javax.swing.JPanel;

public class Screen extends JPanel implements Runnable {
    BufferedImage img = ImageIO.read(new File("bg.png"));
    ImageIcon car = new ImageIcon("sCar.png");
    public int x = 50;

    public Screen() throws IOException {

    }
    @Override
    protected void paintComponent(Graphics g) {
        super.paintComponent(g);
        g.setColor(Color.GREEN);
        car.paintIcon(this, g, x, 50); // I want this to move
        drawBackground(g);
    }
    private void drawBackground(Graphics g) { // testing
        g.setColor(Color.YELLOW);
        g.fillRect(x, 100, 50, 50);
    }
    @Override
    public void run() {
        System.out.println("Hello");
        x = 300;
        repaint();
    }
}

当我的程序到达“Hello”时，我希望它在 x = 300 处重新绘制汽车，但它没有。我应该怎么做才能使这项工作成功？我将它放在 run 方法中，因为我计划稍后将其作为线程运行，但现在，我只想让它移动。

Answer 1

screen 上显示的 Screen 实例与您尝试更新的 Screen 实例不同

public class Fast {

    // screen #1    
    public Screen screen = new Screen();

    public Fast() throws IOException {
        //...
        // Screen #1 on the screen
        frame.add(screen);
        //...
    }
    public static void main(String[] args) throws IOException {
        //...
        // Screen #2, which is not on the screen
        Thread thread = new Thread(new Screen());
        thread.start();
    }
}

我也会小心使用 Thread 来更新 UI 的状态，因为这可能会导致问题并产生意外的结果，相反，我鼓励您使用 Swing 计时器类似这样的事情。

看看Concurrency in Swing和 How to use Swing Timers了解更多详情