Get the in-focus tab after closing a tab

Question

In a JTabbedPane, I associated a custom-made Data object to each added tab. I also have a corresponding Metadata object that shows up in another panel when the tab is selected. The problem I have now is when a tab is closed, the metadata panel shows the metadata of the Data object in the tab that just gets closed. Ideally, I want the panel to show the metadata for the in-focus tab that the user sees. However, the act of closing a tab means the “selected tab” is the tab being closed, so tabpane.getSelectedIndex() would not work. How can I get the tab that is in focus after closing a tab? Thank you in advance!

Answer 1

Devil is in the detail, which you provided none.

I did a quick test and discovered that, ChangeListener is called before ContainerListener, which is a real pain, but, it was always reporting the correct index.

So, what you need to do is marry the two together, so that, both will update the meta data pane when they are called.

import java.awt.EventQueue;
import java.awt.GridBagLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.ContainerEvent;
import java.awt.event.ContainerListener;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JTabbedPane;

public class Test {

    public static void main(String[] args) {
        new Test();
    }

    public Test() {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                JTabbedPane tabbedPane = new JTabbedPane();
                tabbedPane.addTab("One", new TabPane(tabbedPane));
                tabbedPane.addTab("Two", new TabPane(tabbedPane));
                tabbedPane.addTab("Three", new TabPane(tabbedPane));
                tabbedPane.addTab("Four", new TabPane(tabbedPane));

                tabbedPane.addContainerListener(new ContainerListener() {
                    @Override
                    public void componentAdded(ContainerEvent e) {
                    }

                    @Override
                    public void componentRemoved(ContainerEvent e) {
                        System.out.println("Removed " + e.getChild());

                    }
                });

                tabbedPane.addChangeListener(new ChangeListener() {
                    @Override
                    public void stateChanged(ChangeEvent e) {
                        System.out.println(tabbedPane.getSelectedIndex());
                    }
                });

                JFrame frame = new JFrame();
                frame.add(tabbedPane);
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }
        });
    }

    public class TabPane extends JPanel {
        private JTabbedPane parent;

        public TabPane(JTabbedPane parent) {
            this.parent = parent;
            setLayout(new GridBagLayout());
            JButton btn = new JButton("Close");
            add(btn);

            btn.addActionListener(new ActionListener() {
                @Override
                public void actionPerformed(ActionEvent e) {
                    parent.remove(TabPane.this);
                }
            });
        }

    }

}