Question

I have a JTable which can have rows dynamically added by the user. It sits in a JScrollPane, so as the number of rows gets large enough, the scroller becomes active. My desire is that when the user adds a new row, the scroller moves all the way to the bottom, so that the new row is visible in the scrollpane. I’m currently (SSCCE below) trying to use a table model listener to detect when the row is inserted, and force the scrollbar all the way down when the detection is made. However, it seems this detection is “too early,” as the model has updated but the new row has not actually been painted yet, so what happens is the scroller moves all the way to the bottom just before the new row is inserted, and then the new row is inserted just below the end of the pane (out of visibility).

Obviously this approach is wrong somehow. What is the correct approach?

import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;

import javax.swing.BoxLayout;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JScrollBar;
import javax.swing.JScrollPane;
import javax.swing.JSplitPane;
import javax.swing.JTable;
import javax.swing.event.TableModelEvent;
import javax.swing.event.TableModelListener;
import javax.swing.table.DefaultTableModel;

public class TableListenerTest {

    private JFrame frame;
    private JScrollPane scrollPane;
    private JTable table;
    private DefaultTableModel tableModel;

    public static void main(String[] args) {
        EventQueue.invokeLater(new Runnable() {
            public void run() {
                try {
                    TableListenerTest window = new TableListenerTest();
                    window.frame.setVisible(true);
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        });
    }

    public TableListenerTest() {
        initialize();
    }

    private void initialize() {
        frame = new JFrame();
        frame.setBounds(100, 100, 450, 200);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.getContentPane().setLayout(new BoxLayout(frame.getContentPane(), BoxLayout.Y_AXIS));

        JSplitPane splitPane = new JSplitPane();
        frame.getContentPane().add(splitPane);

        scrollPane = new JScrollPane();
        scrollPane.setPreferredSize(new Dimension(100, 2));
        splitPane.setLeftComponent(scrollPane);

        tableModel = new DefaultTableModel(new Object[]{"Stuff"},0);
        table = new JTable(tableModel);
        scrollPane.setViewportView(table);
        table.getModel().addTableModelListener(new TableModelListener() {
            public void tableChanged(TableModelEvent e) {
                if (e.getType() == TableModelEvent.INSERT) {
                    JScrollBar scrollBar = scrollPane.getVerticalScrollBar();
                    scrollBar.setValue(scrollBar.getMaximum());
                }
            }
        });

        JButton btnAddRow = new JButton("Add Row");
        btnAddRow.addMouseListener(new MouseAdapter() {
            @Override
            public void mouseClicked(MouseEvent e) {
                tableModel.addRow(new Object[]{"new row"});
            }
        });
        splitPane.setRightComponent(btnAddRow);
    }
}

EDIT: Updated SSCCE below based on trashgod’s request. This version still does not work, however, if I move the scrolling logic from the table model listener to the button listener as he did, then it does work!

import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Rectangle;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;

import javax.swing.BoxLayout;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JScrollPane;
import javax.swing.JSplitPane;
import javax.swing.JTable;
import javax.swing.event.TableModelEvent;
import javax.swing.event.TableModelListener;
import javax.swing.table.DefaultTableModel;

    public class TableListenerTest {

        private JFrame frame;
        private JScrollPane scrollPane;
        private JTable table;
        private DefaultTableModel tableModel;

        public static void main(String[] args) {
            EventQueue.invokeLater(new Runnable() {
                public void run() {
                    try {
                        TableListenerTest window = new TableListenerTest();
                        window.frame.setVisible(true);
                    } catch (Exception e) {
                        e.printStackTrace();
                    }
                }
            });
        }

        public TableListenerTest() {
            initialize();
        }

        private void initialize() {
            frame = new JFrame();
            frame.setBounds(100, 100, 450, 200);
            frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
            frame.getContentPane().setLayout(new BoxLayout(frame.getContentPane(), BoxLayout.Y_AXIS));

            JSplitPane splitPane = new JSplitPane();
            frame.getContentPane().add(splitPane);

            scrollPane = new JScrollPane();
            scrollPane.setPreferredSize(new Dimension(100, 2));
            splitPane.setLeftComponent(scrollPane);

            tableModel = new DefaultTableModel(new Object[]{"Stuff"},0);
            table = new JTable(tableModel);
            scrollPane.setViewportView(table);
            table.getModel().addTableModelListener(new TableModelListener() {
                public void tableChanged(TableModelEvent e) {
                    if (e.getType() == TableModelEvent.INSERT) {
                        int last = table.getModel().getRowCount() - 1;
                        Rectangle r = table.getCellRect(last, 0, true);
                        table.scrollRectToVisible(r);
                    }
                }
            });

            JButton btnAddRow = new JButton("Add Row");
            btnAddRow.addMouseListener(new MouseAdapter() {
                @Override
                public void mouseClicked(MouseEvent e) {
                    tableModel.addRow(new Object[]{"new row"});
                }
            });
            splitPane.setRightComponent(btnAddRow);
        }
    }

Answer 1

This example uses scrollRectToVisible() to (conditionally) scroll to the last cell rectangle. As a feature you can click on the thumb to suspend scrolling and release to resume.

private void scrollToLast() {
    if (isAutoScroll) {
        int last = table.getModel().getRowCount() - 1;
        Rectangle r = table.getCellRect(last, 0, true);
        table.scrollRectToVisible(r);
    }
}

Addendum: I tried scrollRectToVisible in my SSCCE, and it still exhibits the same problem.

This Action provides both mouse and keyboard control:

JButton btnAddRow = new JButton(new AbstractAction("Add Row") {

    @Override
    public void actionPerformed(ActionEvent e) {
        tableModel.addRow(new Object[]{"new row"});
        int last = table.getModel().getRowCount() - 1;
        Rectangle r = table.getCellRect(last, 0, true);
        table.scrollRectToVisible(r);
    }
});

Addendum: Here’s a variation on your example that illustrates a revised layout strategy.

/** @see https://stackoverflow.com/a/14429388/230513 */
public class TableListenerTest {

    private static final int N = 8;
    private JFrame frame;
    private JScrollPane scrollPane;
    private JTable table;
    private DefaultTableModel tableModel;

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

            @Override
            public void run() {
                TableListenerTest window = new TableListenerTest();
                window.frame.setVisible(true);
            }
        });
    }

    public TableListenerTest() {
        initialize();
    }

    private void initialize() {
        frame = new JFrame();
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setLayout(new BoxLayout(frame.getContentPane(), BoxLayout.X_AXIS));
        tableModel = new DefaultTableModel(new Object[]{"Stuff"}, 0);
        for (int i = 0; i < N; i++) {
            tableModel.addRow(new Object[]{"new row"});
        }
        table = new JTable(tableModel) {

            @Override
            public Dimension getPreferredScrollableViewportSize() {
                return new Dimension(200, table.getRowHeight() * N);
            }
        };
        scrollPane = new JScrollPane();
        scrollPane.setViewportView(table);
        JButton btnAddRow = new JButton(new AbstractAction("Add Row") {

            @Override
            public void actionPerformed(ActionEvent e) {
                tableModel.addRow(new Object[]{"new row"});
                int last = table.getModel().getRowCount() - 1;
                Rectangle r = table.getCellRect(last, 0, true);
                table.scrollRectToVisible(r);
            }
        });
        frame.add(scrollPane);
        frame.add(btnAddRow);
        frame.pack();
    }
}