swing Java JPanel对象已更新，但更新在屏幕上不可见

Question

我对GUI编程非常陌生，不知道如何更新对象并在屏幕上显示更改。我有一门数独课，它扩展了JPanel。我有一个JFrame，数独是其中的一部分。我有一个按钮，它调用函数openFile。以下是它的名称：

private void openFileActionPerformed(java.awt.event.ActionEvent evt) {                                         
    sudoku = FileManagement.openFile(this, sudoku);
}

数独对象有一个9x9网格，当我调试它时，新值就在网格中。但我不知道如何在屏幕上显示新值。我读了一些评论并尝试了数独。验证（），数独。重新绘制（）或只是再次打包JFrame，但它不起作用。所以如果有人告诉我如何修复，我将不胜感激。如果我的解释不充分或不清楚，请告诉我在描述中还需要补充什么。谢谢

编辑-添加代码：

import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.ObjectInputStream;
import javax.swing.JFileChooser;
import javax.swing.JFrame;

public class Sample extends javax.swing.JFrame {
    public Sample() {
        initComponents();
    }

    private void initComponents() {
        sudoku = new sudoku.Sudoku();
        openFile = new javax.swing.JButton();

        openFile.setText("Open");
        openFile.addActionListener(new java.awt.event.ActionListener() {
            public void actionPerformed(java.awt.event.ActionEvent evt) {
                openFileActionPerformed(evt);
            }
        });
        /*sorry for that part - automaticlly generated, don't know how to make it less*/
        javax.swing.GroupLayout layout = new javax.swing.GroupLayout(getContentPane());
        getContentPane().setLayout(layout);
        layout.setHorizontalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(layout.createSequentialGroup()
                .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
                        .addComponent(sudoku)
                    .addGroup(layout.createSequentialGroup()
                        .addComponent(openFile)))));
        layout.setVerticalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(layout.createSequentialGroup()
                .addComponent(sudoku)
                .addComponent(openFile)));
        pack();
    }                     

    private void openFileActionPerformed(java.awt.event.ActionEvent evt) {                                         
        sudoku = openFile(this, sudoku);
    }                                        

    public static void main(String args[]) {
        java.awt.EventQueue.invokeLater(new Runnable() {
            public void run() {
                new Sample().setVisible(true);
            }
        });
    }

    private javax.swing.JButton openFile;
    private sudoku.Sudoku sudoku;                  

    public static Sudoku openFile(JFrame frame, Sudoku sudoku) {
        JFileChooser fileChooser = new JFileChooser();
        fileChooser.setFileSelectionMode(JFileChooser.FILES_ONLY);
        int result = fileChooser.showOpenDialog(frame);
        if (result == JFileChooser.CANCEL_OPTION) {
            return sudoku;
        }

        File fileName = fileChooser.getSelectedFile();

        try (ObjectInputStream input = new ObjectInputStream(new FileInputStream(fileName))) {
            sudoku = (Sudoku) input.readObject();
        } catch (IOException | ClassNotFoundException ioException) {
            System.out.println(ioException);
        }
        return sudoku;
    }
}

Answer 1

解决这个问题的一个快速方法是从JFrame中删除JPanel，更改其值，然后将JPanel重新添加到JFrame。这可以在下面的例子中看到

import java.awt.EventQueue;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;

@SuppressWarnings("serial")
public class PanelFix extends JFrame {
    JFrame frame = this;
    private JPanel view = a();

    PanelFix() {
        super("Panel Fix");
        setSize(400, 400);
        setLocationRelativeTo(null);
        getContentPane().add(view);
        setVisible(true);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    }

    private JPanel a() {
        JPanel panel = new JPanel();
        JButton but = new JButton("Press Me");
        but.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent arg0) {
                getContentPane().remove(view);
                view = b();
                getContentPane().add(view);
                repaint();
                validate();
            }
        });
        panel.add(but);
        return panel;
    }

    private JPanel b() {
        JPanel panel = new JPanel();
        panel.add(new JLabel("Second Panel"));
        return panel;
    }

    public static void main(String[] args) {
        EventQueue.invokeLater(() -> new PanelFix());
    }
}

如果这不能解决问题，比如Andrew Thompson所说的，那么添加一个MCVE。这将使我们能够帮助解决您的确切问题