Accessing JPanel components from a seperate class

January 4, 2022

So I want to have a CardLayout class that switches between a menu page and a main app page, but I want to design those two panels in their own classes, then add an ActionListener and a CardLayout in a different class, and have the ActionListener use a button created in one of the panel classes.

Here is a (Not so short) SSCCE that kind of covers what I’m trying to say:

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

public class MenuPanel extends Frame{
    JPanel menuPanel;
    JButton login;
    JButton signup;

    public MenuPanel(){
        menuPanel = new JPanel(new GridBagLayout());
        login = new JButton("Login");
        signup = new JButton("Signup");
        
        menuPanel.add(login);
        menuPanel.add(signup);
        
    }
}

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

public class MainPanel extends JFrame{
    JPanel menuPanel;
    JButton login;
    JButton signup;

    public MainPanel(){
        mainPanel = new JPanel(new GridBagLayout());=
        
        menuPanel.setBackground(Color.grey);
        
    }
}

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

public class CardLayout extends Frame implements ActionL {
//Now how do I add the frames from the other classes so that I can add them to my CardLayout?
CardLayout cl = new CardLayout();
JPanel panelCont;
    public CardLayout() {
        frame.add(panelCont);

        panelCont = new JPanel(cl);
        //Here is where I'm having trouble
        panelCont.add(menuPanel, "1");
        panelCont.add(mainPanel, "2");

        cl.show(panelCont, "1");

        login.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent arg0) {
                cl.show(panelCont, "2");
            }
        });
    }
}

public class Main {
    public static void main(String[] args) {
        new CardLayout();
    }
}

>Solution :

You cannot add Frames to another component. Frame is a top level component with a native peer. You should subclass from something else (JPanel?) instead

Also, btw what you are doing is not good design. Generally, in MVC Swing design, all view and control aspects should be in one class. Don’t split the view into multiple classes unless each of those classes stands up as its own reusable widget