Using JTabbedPane with JPanels that need to share data

Question

In my application, I have several custom JPanels added to a JTabbedPane. A single JPanel offers a piece of functionality, I've added them to JTabbedPane so that the user can switch between modules easily.

All of those custom JPanels operate on the same set of data, meaning if one of the modules has to change something in the data (for instance, a List), all other panels should be aware of that change and react accordingly.

However, with JTabbedPane, you first need to instantiate those JPanels to add them to JTabbedPane - and you do it once.

I have one problem - suppose user adds something to the collection in panel A (which is shared by all those panels) and switches to panel B. What should happen in this case? How is B supposed to know that something has been added to that collection?

My idea was to simply detect a tab switch event, and call the method of B to take the new data into account. But I feel this is not how it should be done.

What could you suggest?

Answer 1

In the example below, each panel in the tabbed pane has its own JComboBox that listens to a common ComboBoxModel. When the common model is updated, by clicking Update, each listening JComboBox sees the change.

I never need any two combo boxes to share a model. My panels contain completely different JComponent instances, but the look and data those components display depend on several collections common to all of those panels.

You may be able to leverage the observer pattern, examined here. The exact details depend on your use case, but the PropertyChangeListener examples are worth studying.

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.FlowLayout;
import java.awt.event.ActionEvent;
import java.util.Date;
import javax.swing.AbstractAction;
import javax.swing.DefaultComboBoxModel;
import javax.swing.JButton;
import javax.swing.JComboBox;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JTabbedPane;

/**
 * @see https://stackoverflow.com/a/37514928/230513
 * @see https://stackoverflow.com/questions/8752037
 * @see https://stackoverflow.com/a/37222598/230513
 */
public class TabTest {

    private static final int N = 5;
    private final JTabbedPane pane = new JTabbedPane();
    private final DefaultComboBoxModel model = new DefaultComboBoxModel(
        new String[]{"Alpher", "Bethe", "Gamow", "Dirac", "Einstein"});

    public TabTest() {
        for (int i = 0; i < N; i++) {
            Color color = Color.getHSBColor((float) i / N, 1, 1);
            pane.add("Tab " + String.valueOf(i), new TabContent(i, color));
        }
    }

    private class TabContent extends JPanel {

        private TabContent(int i, Color color) {
            setOpaque(true);
            setBackground(color);
            add(new JComboBox(model));
        }

        @Override
        public Dimension getPreferredSize() {
            return new Dimension(320, 240);
        }
    }

    private void display() {
        JFrame f = new JFrame("TabColors");
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.add(pane);
        JPanel p = new JPanel(new FlowLayout(FlowLayout.RIGHT));
        p.add(new JButton(new AbstractAction("Update") {
            @Override
            public void actionPerformed(ActionEvent e) {
                model.addElement(new Date());
            }
        }));
        f.add(p, BorderLayout.SOUTH);
        f.pack();
        f.setLocationRelativeTo(null);
        f.setVisible(true);
    }

    public static void main(String[] args) {
        EventQueue.invokeLater(new Runnable() {

            @Override
            public void run() {
                new TabTest().display();
            }
        });
    }
}