paintComponent不可见java

Question

我想将其添加到另一个JPanel中，但它在那里不可见。我的其他Jpanel被称为bottomPanel。 paintComponent应该显示在底部面板

bottomPanel.setLayout(null); 
TestPane tp = new TestPane(); 
bottomPanel.add(tp); 

我已经扩展了Jpanel。

public class TestPane extends JPanel { 
    @Override 
    public Dimension getPreferredSize() { 
     return new Dimension(200, 200); 
    } 


    @Override 
    public void paintComponent(Graphics g) { 
     super.paintComponent(g); 
     Graphics2D g2d = (Graphics2D) g.create(); 
     int width = getWidth() - 100; 
     int height = getHeight() - 100; 
     int x = (getWidth() - width)/2; 
     int y = (getHeight() - height)/2; 
     g2d.setColor(Color.RED); 
     g2d.drawRect(x, y, width, height); 
     g2d.dispose(); 
    } 

} 

Answer 1

的问题开始：

bottomPanel.setLayout(null); 

Java GUI必须使用不同语言环境中使用不同PLAF的不同OS，屏幕大小，屏幕分辨率等。因此，它们不利于像素的完美布局。请使用布局管理器，或combinations of them以及white space的布局填充和边框。

而在未来，张贴MCVE而不是300行代码与无关的补充，如文件I/O，表，行分拣机等

Answer 2

对我的作品......

import java.awt.BorderLayout; 
import java.awt.Color; 
import java.awt.Dimension; 
import java.awt.Graphics; 
import java.awt.Graphics2D; 
import javax.swing.JFrame; 
import javax.swing.JPanel; 
import javax.swing.SwingUtilities; 

public class Test { 

    public static void main(String[] args) { 
     new Test(); 
    } 

    public Test() { 
     SwingUtilities.invokeLater(new Runnable() { 
      @Override 
      public void run() { 
       JFrame frame = new JFrame(); 
       JPanel outer = new JPanel(new BorderLayout()); 
       outer.add(new TestPane()); 
       frame.add(outer); 
       frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); 
       frame.pack(); 
       frame.setLocationRelativeTo(null); 
       frame.setVisible(true); 
      } 
     }); 
    } 

    public class TestPane extends JPanel { 

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

     @Override 
     public void paintComponent(Graphics g) { 
      super.paintComponent(g); 
      Graphics2D g2d = (Graphics2D) g.create(); 
      int width = getWidth() - 100; 
      int height = getHeight() - 100; 
      int x = (getWidth() - width)/2; 
      int y = (getHeight() - height)/2; 
      g2d.setColor(Color.RED); 
      g2d.drawRect(x, y, width, height); 
      g2d.dispose(); 
     } 

    } 

} 

考虑提供runnable example这表明你的问题