Question

我尝试编写一个代码来从左上角到右下角绘制一个椭圆形运行。但是当我运行程序时，它会在应用程序上显示空白屏幕。为什么会这样？

这是我的代码：

import javax.swing.*;
import java.awt.*;

public class SimpleAnimation {
    int x = 70;
    int y = 70;

    public static void main(String[] arg){
        SimpleAnimation gui = new SimpleAnimation();
        gui.go();
    }

    public void go(){
        JFrame frame = new JFrame();
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        MyDrawPanel drawPanel = new MyDrawPanel();

        frame.getContentPane().add(drawPanel);
        frame.setSize(300, 300);
        frame.setVisible(true);

        for (int i = 0; i < 130; i++){
            x++;
            y++;

            drawPanel.repaint();

            try{
                Thread.sleep(50);
            } catch(Exception ex){}
        }
    } // close go() method

    class MyDrawPanel extends JPanel{
        @Override
        public void paintComponents(Graphics g) {
            g.setColor(Color.green);
            g.fillOval(x, y, 40, 40);
        }
    } // close inner class
} // close outer class

Answer 1

您应该覆盖paintComponent()而不是paintComponents()。

所以将public void paintComponents() {...}更改为public void paintComponent() {...}

但仅仅是提示：

尝试使用Timers而不是Threads。总是尽量不要乱摇摆线。在您的情况下，您可以使用javax.swing.Timer以50 ms的间隔调用重绘：

counter = 0;
t = new Timer(50, new ActionListener() {
    @Override
    public void actionPerformed(ActionEvent e) {
        if(counter>=130)
            t.stop();

        counter++;
        x++;
        y++;
        drawPanel.repaint();
    }
});
t.start();

javax.swing.Timer t和int counter是您班级的成员变量。

祝你好运。

Answer 2

您没有致电super.paintComponent(g);，也需要拨打paintComponents而不是repaint方法。请尝试使用以下代码。我希望它有所帮助：）

import java.awt.Color;
import java.awt.Graphics;

import javax.swing.JFrame;
import javax.swing.JPanel;

public class SimpleAnimation {
  int x = 70;
  int y = 70;

  public static void main(String[] arg) {
    SimpleAnimation gui = new SimpleAnimation();
    gui.go();
  }

  public void go() {
    JFrame frame = new JFrame();
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

    MyDrawPanel drawPanel = new MyDrawPanel();

    frame.getContentPane().add(drawPanel);
    frame.setSize(300, 300);
    frame.setVisible(true);



    for (int i = 0; i < 130; i++) {
      x++;
      y++;

      drawPanel.paintComponents(drawPanel.getGraphics());

      try {
        Thread.sleep(50);
      } catch (Exception ex) {
      }
    }
  } // close go() method

  class MyDrawPanel extends JPanel {
    @Override
    public void paintComponents(Graphics g) {
      // TODO Auto-generated method stub
      super.paintComponent(g); 
      g.drawOval(50, 50, 50, 50);
      g.setColor(Color.green);
      g.fillOval(x, y, 40, 40);
    }
  } // close inner class
} // close outer class

图形应用程序只显示空白屏幕

2 个答案: