我制作了自己的JPanel子类，称为SubPatternPanel 。 我想在框架中使用它来绘制网格，但是当我从框架中为SubPatternPanel调用repaint() ，它不起作用。

运行时，框架带有“新建”按钮显示。 当按下“新建”按钮时，面板上应绘制一个网格，但不是，并且我也找不到原因。

以下是SubPatternPanel的代码：

package View;

import java.awt.Color;

import java.awt.Dimension;

import java.awt.Graphics;

import javax.swing.JPanel;

public class SubPatternPanel extends JPanel

{

public SubPatternPanel()

{

setLayout(null);

setBackground(Color.white);

setPreferredSize(new Dimension(240, 240));

}

@Override

public void paintComponent(Graphics g)

{

super.paintComponent(g);

g.setColor(Color.black);

for (int i = 0; i < 3; i++)

{

for (int j = 0; j < 3; j++)

{

g.drawLine(i * 80, j * 80, 240, j * 80);

g.drawLine(i * 80, j * 80, i * 80, 240);

}

}

}

}

大多数的框架代码都是自动生成的，因此我不确定为获得更清晰的图片而遗漏的内容。

package View;

import java.awt.BorderLayout;

public class PatternsMainFrame extends javax.swing.JFrame

{

private SubPatternPanel subPatternPanel;

public PatternsMainFrame()

{

initComponents();

subPatternPanel = new SubPatternPanel();

patternStartPanel.add(subPatternPanel, BorderLayout.CENTER);

}

@SuppressWarnings("unchecked")

//

private void initComponents()

{

patternStartPanel = new javax.swing.JPanel();

newButton = new javax.swing.JButton();

setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);

javax.swing.GroupLayout patternStartPanelLayout = new javax.swing.GroupLayout(patternStartPanel);

patternStartPanel.setLayout(patternStartPanelLayout);

patternStartPanelLayout.setHorizontalGroup(

patternStartPanelLayout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)

.addGap(0, 277, Short.MAX_VALUE)

);

patternStartPanelLayout.setVerticalGroup(

patternStartPanelLayout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)

.addGap(0, 278, Short.MAX_VALUE)

);

newButton.setText("New");

newButton.addActionListener(new java.awt.event.ActionListener()

{

public void actionPerformed(java.awt.event.ActionEvent evt)

{

newButtonActionPerformed(evt);

}

});

javax.swing.GroupLayout layout = new javax.swing.GroupLayout(getContentPane());

getContentPane().setLayout(layout);

layout.setHorizontalGroup(

layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)

.addGroup(layout.createSequentialGroup()

.addContainerGap()

.addComponent(patternStartPanel, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)

.addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED, 248, Short.MAX_VALUE)

.addComponent(newButton)

.addGap(112, 112, 112))

);

layout.setVerticalGroup(

layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)

.addGroup(layout.createSequentialGroup()

.addContainerGap()

.addComponent(patternStartPanel, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)

.addContainerGap())

.addGroup(layout.createSequentialGroup()

.addGap(24, 24, 24)

.addComponent(newButton)

.addContainerGap(javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE))

);

pack();

}

private void newButtonActionPerformed(java.awt.event.ActionEvent evt)

{

subPatternPanel.repaint();

}

public static void main(String args[])

{

try

{

for (javax.swing.UIManager.LookAndFeelInfo info : javax.swing.UIManager.getInstalledLookAndFeels())

{

if ("Nimbus".equals(info.getName()))

{

javax.swing.UIManager.setLookAndFeel(info.getClassName());

break;

}

}

} catch (ClassNotFoundException ex)

{

java.util.logging.Logger.getLogger(PatternsMainFrame.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);

} catch (InstantiationException ex)

{

java.util.logging.Logger.getLogger(PatternsMainFrame.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);

} catch (IllegalAccessException ex)

{

java.util.logging.Logger.getLogger(PatternsMainFrame.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);

} catch (javax.swing.UnsupportedLookAndFeelException ex)

{

java.util.logging.Logger.getLogger(PatternsMainFrame.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);

}

java.awt.EventQueue.invokeLater(new Runnable()

{

public void run()

{

new PatternsMainFrame().setVisible(true);

}

});

}

private javax.swing.JButton newButton;

private javax.swing.JPanel patternStartPanel;

}