在具有卡片布局的JPanel中的两个JPanel之间交换

Question

I'm trying to get two jpanels to swap via buttons on those SPECIFIC panels, i don't want general buttons on both panels like normal card layout uses that repeat on both. I've tried to have a button called 'add' on main panel lead to the next page and a button on next page called 'back' lead to main panel. However for some reason it isn't working. I don't want two JPanels on the JFrame because I will be adding the JPanel to a tabbed pane later. Heres what I have already:

Controller:

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

public class Controller extends JPanel {

    private static Controller instance = new Controller();

    JPanel cards;
    Main mainPanel;
    NextPage nextPage;

    public Controller() {
        setLayout(new BorderLayout());
        setSize(810, 510);
        cards = new JPanel(new CardLayout());

        mainPanel = new Main();
        nextPage = new NextPage();
        cards.add(mainPanel, "Main");
        cards.add(nextPage, "Next");
        add(cards);
        setVisible(true);
    }

    private static void createAndShowGUI() {
        JFrame frame = new JFrame("MainPanel");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        Controller con = new Controller();
        frame.getContentPane().add(con);
        frame.setSize(800, 600);
        frame.setVisible(true);
    }

    public static void main(String[] args) {
        javax.swing.SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                createAndShowGUI();
            }
        });
    }


    public void changeCard(String card) {
        CardLayout cl = (CardLayout) (cards.getLayout());
        cl.show(cards, card);
    }

    public static Controller getInstance() {
        return instance;
    }
}

Main:

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

public class Main extends JPanel implements ActionListener {

    private JButton search, add, delete;
    private JTextField textField;

    public Main() {

        search = new JButton("Search");
        add = new JButton("Add");
        delete = new JButton("Delete");
        textField = new JTextField(20);
        add.addActionListener(this);
        delete.addActionListener(this);
        setLayout(new BorderLayout());
        JPanel top = new JPanel();
        top.add(search);
        add(top, BorderLayout.NORTH);
        JPanel bottom = new JPanel();
        bottom.add(add);
        bottom.add(delete);
        add(bottom, BorderLayout.SOUTH);
        setVisible(true);
        setSize(400, 500);
    }

    public void actionPerformed(ActionEvent e) {
        if (e.getSource() == add) {
            Controller.getInstance().changeCard("Next");
        } else if (e.getSource() == delete) {
           System.out.println("do something");
        }
    }

}

For next page:

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

public class NextPage extends JPanel implements ActionListener {

    private JButton back;
    private JTextField textField;

    public NextPage() {
        back = new JButton("Back");
        textField = new JTextField(20);
        back.addActionListener(this);
        setLayout(new BorderLayout());
        add(back);
        setVisible(true);
        setSize(400, 500);
    }

    public void actionPerformed(ActionEvent e) {
        if (e.getSource() == back) {
            Controller.getInstance().changeCard("Next");
        }

    }
}

Answer 1

Change your Controller like this:

private static Controller instance;

...

private static void createAndShowGUI() {
    JFrame frame = new JFrame("MainPanel");
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    instance = new Controller();
    frame.getContentPane().add(instance);
    frame.setSize(800, 600);
    frame.setVisible(true);
}

You actually created everything on an instance of Controller and showed it, but used another one to manage your events. The multiple calls to the Controller constructor should have ringed a bell, because you only want one Controller .