Override a frames next/prev buttons using cardLayout

Question

Updated: The thing is that I want my prev button to only work if I have been to that one before. For instance, if I logged in and click next, I should be able to go back one step. But not two.

public class MainFrame {

    private static void createAndShowGUI() {
        JFrame frame = new JFrame("Dimensions helper");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setLocationRelativeTo(null);

        final JPanel contentPane = new JPanel();
        contentPane.setLayout(new CardLayout(200, 200));

        Window1 win1 = new Window1();
        contentPane.add(win1);
        Window2 win2 = new Window2();
        contentPane.add(win2);
        Window3 win3 = new Window3();
        contentPane.add(win3);

        JPanel buttonPanel = new JPanel(); 
        final JButton previousButton = new JButton("< PREVIOUS");
        final JButton nextButton = new JButton("NEXT >");
        final JButton cancelButton = new JButton("CANCEL");
        buttonPanel.add(cancelButton);
        buttonPanel.add(previousButton);
        buttonPanel.add(nextButton);

        previousButton.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent ae) {
                Verifiable verifiable = null;
                Component[] contents = contentPane.getComponents();
                for(Component component : contents) {
                    if(component.isVisible() && component instanceof Verifiable) {
                        verifiable = (Verifiable)component;
                    }
                }
                if(verifiable != null && verifiable.isDataValid()) {
                    CardLayout cardLayout = (CardLayout) contentPane.getLayout();
                    cardLayout.previous(contentPane);
                }
            }
        });

        nextButton.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent ae) {
                Verifiable verifiable = null;
                Component[] contents = contentPane.getComponents();
                for(Component component : contents) {
                    if(component.isVisible() && component instanceof Verifiable) {
                        verifiable = (Verifiable)component;
                    }
                }
                if(verifiable != null && verifiable.isDataValid()) {
                    CardLayout cardLayout = (CardLayout) contentPane.getLayout();
                    cardLayout.next(contentPane); 
                }
            }
        });

        cancelButton.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent ae) {
                System.exit(0);
            }

        });

        frame.add(contentPane);
        frame.add(buttonPanel, BorderLayout.PAGE_END);
        frame.pack();
        frame.setVisible(true);
    }

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

Window1.java

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

public class Window1 extends JPanel implements Verifiable {

    JTextField txtUsername = new JTextField();
    JPasswordField txtPassword = new JPasswordField();

    public Window1() {
        init();
    }

    private void init() {
        setLayout(new GridLayout(2, 2));
        JLabel lblUsername = new JLabel("Username:", JLabel.CENTER);
        txtUsername = new JTextField();

        JLabel lblPassword = new JLabel("Password:", JLabel.CENTER);
        txtPassword = new JPasswordField();

        add(lblUsername);
        add(txtUsername);
        add(lblPassword);
        add(txtPassword);
        String title = "Log in";
        setBorder(BorderFactory.createTitledBorder(title));
    }

    @Override
    public boolean isDataValid() {
        if(txtUsername.getText().equals("foo") &&
                java.util.Arrays.equals(txtPassword.getPassword(), "bar".toCharArray())) {
            return true;
        } else {
            JOptionPane.showMessageDialog(this, "Fel användarnamn och/eller lösenord", 
                    "Error", JOptionPane.ERROR_MESSAGE);
            return false;
        }
    }
}

Answer 1

For example, create an interface, Verifiable, with a boolean method, isDataValid():

interface Verifiable {
   boolean isDataValid();
}

and have your panel classes implement the interface so that each panel can validate its own data.

class Window1 extends JPanel implements Verifiable {

   JTextField txtUsername = new JTextField();
   JPasswordField txtPassword = new JPasswordField();

   public Window1() {
      init();
   }

   private void init() {

      setLayout(new GridLayout(2, 2));
      JLabel lblUsername = new JLabel("Username:", JLabel.CENTER);

      JLabel lblPassword = new JLabel("Password:", JLabel.CENTER);

      add(lblUsername);
      add(txtUsername);
      add(lblPassword);
      add(txtPassword);
      String title = "Use \"foo\" and \"bar\"";
      setBorder(BorderFactory.createTitledBorder(title ));
   }

   @Override
   public boolean isDataValid() {
      return txtUsername.getText().equals("foo") && 
            java.util.Arrays.equals(txtPassword.getPassword(), "bar".toCharArray());
   }
}

Then check that the current displayed panel's data is valid in next and previous JButton's ActionListener.

  nextButton.addActionListener(new ActionListener() {
     public void actionPerformed(ActionEvent ae) {
        Verifiable verifiable = null;
        Component[] contents = contentPane.getComponents();
        for (Component component : contents) {
           if (component.isVisible() && component instanceof Verifiable) {
              verifiable = (Verifiable) component;
           }
        }
        if (verifiable != null && verifiable.isDataValid()) {
           CardLayout cardLayout = (CardLayout) contentPane.getLayout();
           cardLayout.next(contentPane);
        }

     }
  });