Question

我一直在努力想出一个针对物理项目的程序，但我遇到了问题。这是代码：

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

public class Cannon extends JFrame {
  Cannon() {
  setTitle("Cannonball Experiment");
  setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

  Container c = getContentPane();
  c.setLayout(new FlowLayout());

  c.add(new ImagePanel());
  c.add(new ModifierPanel());

  setSize(400,600);
  setVisible(true);
       }

   class ImagePanel extends JPanel {
  public void paintComponent(Graphics g) {
     super.paintComponent(g);
     g.drawRect(0,100,200,300);
  }
   }

   class ModifierPanel extends Panel {
  JLabel Text = new JLabel("Speed"); 
  JTextField Tf = new JTextField(10);

  ModifierPanel() {
     add(Text);
     add(Tf);
  }
   }
   public static void main(String[] args) {
  Cannon frame = new Cannon();
   }
}

ModifierPanel显示正常，但我在修改器之前添加的JPanel未显示。

Answer 1

JPanel ImageJPanel没有显示任何内容，因此其尺寸为（0,0）。尝试为您的JPanel提供尺寸覆盖方法getPreferredSize，如下所示：

class ImagePanel extends JPanel {
   @Override
   public void paintComponent(Graphics g) {
        super.paintComponent(g);
        g.drawRect(0,100,200,300);
   }

   @Override
   public Dimension getPreferredSize() {
        return new Dimension(500,300); //for example
   }
}

您正在使用尊重FlowLayout的{{1}}，因此您不会遇到任何问题。试着让我知道......

Answer 2

在图像面板中尝试缓冲图像..

 public class ImagePanel extends JPanel{

private BufferedImage image;

public ImagePanel() {
   try {                
      image = ImageIO.read(new File("specify image name and path"));
   } catch (IOException ex) {
        //  exception...
   }
}

@Override
protected void paintComponent(Graphics g) {
    super.paintComponent(g);
    g.drawImage(image, 0, 0, null);           
}

自定义绘制的JPanel不会出现在JFrame中

2 个答案: