Java 初始化后如何向JFrame添加组件？

我有一个JFrame。当它第一次启动时，它不会（故意）加载按钮，因为它依赖于一个布尔值sessionExists，默认情况下该值为false。当用户单击add启动JDialog并在该JDialog中单击Ok时，它会将JFrame的sessionExists值设置为true

我希望代码执行的操作：

单击Ok之后，我希望JFrame更新自身，并用文本“new button”显示该按钮，因为sessionExists现在为true

当前行为：

当前，用户单击“确定”，JDialog将退出，但父JFrame将保持不变，并且按钮不会出现

我尝试过的解决方案：

我尝试在JFrame中使用.validate和.repaint（）刷新它，以便显示按钮，但它似乎不起作用

我应该如何实现预期的行为？我应该使用CardLayout吗

我用下面的代码重现了这个问题。我的实际程序依赖于文件是否存在，而不是布尔变量

JFrame

import java.awt.BorderLayout;
import java.awt.EventQueue;

import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.border.EmptyBorder;

import javax.swing.JButton;
import javax.swing.JDialog;

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

public class MainMenu extends JFrame {

    private JPanel contentPane;
    
    MainMenu thisFrame = this;
    
    boolean sessionExists = false;

    public static void main(String[] args) {
        EventQueue.invokeLater(new Runnable() {
            public void run() {
                try {
                    MainMenu frame = new MainMenu();
                    frame.setVisible(true);
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        });
    }

    public MainMenu() {
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setBounds(100, 100, 450, 300);
        contentPane = new JPanel();
        contentPane.setBorder(new EmptyBorder(5, 5, 5, 5));
        contentPane.setLayout(new BorderLayout(0, 0));
        setContentPane(contentPane);
        
        if (sessionExists == true) {
            JButton btnNewButton = new JButton("New button");
            contentPane.add(btnNewButton, BorderLayout.CENTER);
        }
        
        JButton btnNewButton_1 = new JButton("Add Button");
        btnNewButton_1.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent arg0) {
                Add newTask = new Add(thisFrame);
                newTask.setDefaultCloseOperation(JDialog.DISPOSE_ON_CLOSE);
                newTask.setTitle("Add Task");
                newTask.setVisible(true);
            }
        });
        contentPane.add(btnNewButton_1, BorderLayout.SOUTH);
    }
    
    public void refresh() {
        this.validate();
        this.repaint();
    }

}

“添加”JDialog

当您尝试添加时，如果（session==true），则不调用它。与此相反，创建像adding（）这样的新函数，并从Add JDialog类调用它，它就会工作。（您会注意到，您不必使用session==true，因为您可以通过这种方式直接调用该函数。但是为了您的理解，我没有更改它。） 示例代码：

主菜单：

public class MainMenu extends JFrame {

    private JPanel contentPane;
    
    MainMenu thisFrame = this;
    
    boolean sessionExists = false;

    public static void main(String[] args) {
        EventQueue.invokeLater(new Runnable() {
            public void run() {
                try {
                    MainMenu frame = new MainMenu();
                    frame.setVisible(true);
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        });
    }

    public MainMenu() {
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setBounds(100, 100, 450, 300);
        contentPane = new JPanel();
        contentPane.setBorder(new EmptyBorder(5, 5, 5, 5));
        contentPane.setLayout(new BorderLayout(0, 0));
        setContentPane(contentPane);
        
        
        
        JButton btnNewButton_1 = new JButton("Add Button");
        btnNewButton_1.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent arg0) {
                Add newTask = new Add(thisFrame);
                newTask.setDefaultCloseOperation(JDialog.DISPOSE_ON_CLOSE);
                newTask.setTitle("Add Task");
                newTask.setVisible(true);
                
            }
        });
        contentPane.add(btnNewButton_1, BorderLayout.SOUTH);
    }
    
    public void adding() {
        if (sessionExists == true) {
            JButton btnNewButton = new JButton("New button");
            contentPane.add(btnNewButton, BorderLayout.CENTER);
        }
    }
    
    public void refresh() {
        this.validate();
        this.repaint();
    }

}

加：

public class MainMenu extends JFrame {

    private JPanel contentPane;
    
    MainMenu thisFrame = this;
    
    boolean sessionExists = false;

    public static void main(String[] args) {
        EventQueue.invokeLater(new Runnable() {
            public void run() {
                try {
                    MainMenu frame = new MainMenu();
                    frame.setVisible(true);
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        });
    }

    public MainMenu() {
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setBounds(100, 100, 450, 300);
        contentPane = new JPanel();
        contentPane.setBorder(new EmptyBorder(5, 5, 5, 5));
        contentPane.setLayout(new BorderLayout(0, 0));
        setContentPane(contentPane);
        
        
        
        JButton btnNewButton_1 = new JButton("Add Button");
        btnNewButton_1.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent arg0) {
                Add newTask = new Add(thisFrame);
                newTask.setDefaultCloseOperation(JDialog.DISPOSE_ON_CLOSE);
                newTask.setTitle("Add Task");
                newTask.setVisible(true);
                
            }
        });
        contentPane.add(btnNewButton_1, BorderLayout.SOUTH);
    }
    
    public void adding() {
        if (sessionExists == true) {
            JButton btnNewButton = new JButton("New button");
            contentPane.add(btnNewButton, BorderLayout.CENTER);
        }
    }
    
    public void refresh() {
        this.validate();
        this.repaint();
    }

}

public class Add extends JDialog {

    private final JPanel contentPanel = new JPanel();

    public Add(MainMenu parentJFrame) {
        setBounds(100, 100, 450, 300);
        getContentPane().setLayout(new BorderLayout());
        contentPanel.setLayout(new FlowLayout());
        contentPanel.setBorder(new EmptyBorder(5, 5, 5, 5));
        getContentPane().add(contentPanel, BorderLayout.CENTER);
        {
            JPanel buttonPane = new JPanel();
            buttonPane.setLayout(new FlowLayout(FlowLayout.RIGHT));
            getContentPane().add(buttonPane, BorderLayout.SOUTH);
            {
                JButton okButton = new JButton("OK");
                okButton.addActionListener(new ActionListener() {
                    public void actionPerformed(ActionEvent e) {
                        parentJFrame.sessionExists = true;
                        parentJFrame.adding();
                        parentJFrame.refresh();
                        dispose();
                    }
                });
                okButton.setActionCommand("OK");
                buttonPane.add(okButton);
                getRootPane().setDefaultButton(okButton);
            }
            {
                JButton cancelButton = new JButton("Cancel");
                cancelButton.setActionCommand("Cancel");
                buttonPane.add(cancelButton);
            }
        }
    }

}