如何滚动到JTable中的最后一行

Question

I am trying to use JTable in the way where new data record are added to the end. The strange thing is the scroll bar does not go to the end of the table; instead, it always shows the second from the last. Any way to tell the scroll bar to always go to the end of the table?

Here is part of my code:

table.scrollRectToVisible(table.getCellRect(table.getRowCount()-1, 0, true));

Answer 1

I just ran into this problem - there is actually nothing wrong with that line of code; the problem lies in when you execute it.

If you're, like me, trying to execute it immediately after manipulating the TableModel (even via invokeLater ) or by using a TableModelListener , you'll get the problem you're describing. The problem is that while the model has been updated with the new data ( table.getRowCount() is simply a pass-through to the getRowCount() method on your TableModel ), the JTable component visually has not.

When you execute that line of code in the previously described places, you're actually trying to tell the JScrollPane ( JTable.scrollRectToVisible defers any action to a parent that can provide scrolling behaviour, eg JScrollPane ) to scroll beyond the end of the enclosed JTable component. It refuses to do that, and instead scrolls to the current end of the JTable component instead.

At some point later, the JTable component updates itself visually, and adds the newly added row underneath the row scrolled to earlier. You can verify that that line of code works by adding a button that executes it independently of the code that adds new rows, eg

private JTable _table = new JTable();
...
JButton b = new JButton("Force scroll to bottom");
b.addActionListener(new ActionListener() {
    public void actionPerformed(ActionEvent e) { 
        _table.scrollRectToVisible(_table.getCellRect(_table.getRowCount()-1, 0, true));
    }
});
this.add(b);

The solution to this problem is a little indirect, but does work reliably in my testing. Because the issue lies in the visual side of things, I decided to hook into the ComponentListener instead, which provides, among other things, a componentResized method. Whenever a row is added or removed, the JTable resizes, even if it cannot be seen visually due to the JScrollPane's viewport. Therefore just run that line of code in that listener method, and things will work as expected.

private JTable _table = new JTable();
...
_table.addComponentListener(new ComponentAdapter() {
    public void componentResized(ComponentEvent e) {
        _table.scrollRectToVisible(_table.getCellRect(_table.getRowCount()-1, 0, true));
    }
});

Answer 2

Thanks to Sam's answer and another page I found elsewhere, I was able to solve this problem.

I figured I'd share my solution so the next guy doesn't have to piece it all together.

Enjoy!

import java.awt.Rectangle;
import java.awt.event.ComponentAdapter;
import java.awt.event.ComponentEvent;
import java.security.NoSuchAlgorithmException;
import java.security.SecureRandom;
import java.text.SimpleDateFormat;
import java.util.Date;

import javax.swing.JFrame;
import javax.swing.JScrollPane;
import javax.swing.JTable;
import javax.swing.JViewport;
import javax.swing.ScrollPaneConstants;
import javax.swing.SwingUtilities;
import javax.swing.table.DefaultTableModel;

/**
 * Demonstrate displaying a specific cell in a JTable when a row is added.
 * <p>
 * The Table Row Index is displayed in one of the table's columns.
 * <p>
 * The cell containing the Value will be selected for displaying.
 * <p>
 * The specified cell will be made visible and, if possible, positioned in the center of the Viewport.
 * <p>
 * The code works regardless of:
 * <ul>
 * <li>Whether or not the table data is sorted</li>
 * <li>The position/visibility of the "Value" column</li>
 * </ul>
 */
public class JTableScrollToRow
{
    static SecureRandom         random;
    private DefaultTableModel   dtm;

    static
    {
        try
        {
            random = SecureRandom.getInstance("SHA1PRNG");
            int seed = Integer.parseInt((new SimpleDateFormat("SSS")).format(new Date()));
            random.setSeed(random.generateSeed(seed));
        }
        catch (NoSuchAlgorithmException e)
        {
            e.printStackTrace();
        }
    }

    public void buildGUI()
    {
        Object[][] data = {};
        Object colNames[] = {
                "Value",
                "TableRowIx",
                "Column A",
                "Column B",
                "Column C",
                "Column D",
                "Column E",
                "Column F" };

        dtm = new DefaultTableModel(data, colNames);
        final JTable sampleTable = new JTable(dtm);
        sampleTable.setDragEnabled(false);
        sampleTable.setAutoCreateRowSorter(true);

        // Turn off auto-resizing to allow for columns moved out of the Viewport
        sampleTable.setAutoResizeMode(JTable.AUTO_RESIZE_OFF);

        // Populate the table with some data
        for (int x = 0; x < 200; x++)
        {
            addRow(x);
        }

        // Create a ScrollPane
        JScrollPane sp = new JScrollPane(sampleTable);

        // Provide a horizontal scroll bar so that columns can be scrolled out of the Viewport
        sp.setHorizontalScrollBarPolicy(ScrollPaneConstants.HORIZONTAL_SCROLLBAR_ALWAYS);

        final JFrame f = new JFrame();
        f.getContentPane().add(sp);
        f.setTitle("JTable cell display example");
        f.pack();
        f.setLocationRelativeTo(null);
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.setVisible(true);

        // Create a thread that periodically adds a row to the table
        Thread rowAdder = new Thread(new Runnable()
        {
            @Override
            public void run()
            {
                do
                {
                    try
                    {
                        int secs = 5;
                        Thread.sleep(secs * 1000);
                    }
                    catch (InterruptedException e)
                    {
                        e.printStackTrace();
                    }

                    // Add a row
                    addRow(dtm.getRowCount());
                } while (true);
            }
        });
        rowAdder.start();

        // Add the custom ComponentListener
        sampleTable.addComponentListener(new JTableCellDisplayer(sampleTable));
    }

    /**
     * Display a table row when it is added to a JTable.<br>
     * Details available at <a
     * href="http://stackoverflow.com/questions/4890282/howto-to-scroll-to-last-row-on-jtable">StackOverflow</a>.
     * <p>
     * <b>Key information:</b> Whenever a row is added or removed the JTable resizes. This occurs even if the row is
     * outside of the JScrollPane's Viewport (i.e., the row is not visible).
     */
    class JTableCellDisplayer extends ComponentAdapter
    {
        boolean selRow      = false;
        boolean selCol      = false;
        boolean firstTime   = true;
        boolean selectData  = false;
        JTable  table;

        public JTableCellDisplayer(JTable jTable)
        {
            table = jTable;
        }

        @Override
        public void componentResized(ComponentEvent e)
        {
            if (firstTime)
            {
                firstTime = false;
                return;
            }

            int viewIx = table.convertRowIndexToView(table.getRowCount() - 1);

            if (!selRow
                    && !selCol)
            {
                System.out.println(" - Select nothing - selectData="
                        + selectData);
            }
            else if (selRow
                    && !selCol)
            {
                System.out.println(" - Select row only - selectData="
                        + selectData);
            }
            else if (!selRow
                    && selCol)
            {
                System.out.println(" - Select column only - selectData="
                        + selectData);
            }
            else
            {
                System.out.println(" - Select cell - selectData="
                        + selectData);
            }

            // If data should be selected, set the selection policies on the table.
            if (selectData)
            {
                table.setRowSelectionAllowed(selRow);
                table.setColumnSelectionAllowed(selCol);
            }

            // Scroll to the VALUE cell (columnIndex=0) that was added
            displayTableCell(table, viewIx, table.convertColumnIndexToView(0), selectData);

            // Cycle through all possibilities
            if (!selRow
                    && !selCol)
            {
                selRow = true;
            }
            else if (selRow
                    && !selCol)
            {
                selRow = false;
                selCol = true;
            }
            else if (!selRow
                    && selCol)
            {
                selRow = true;
                selCol = true;
            }
            else
            {
                selRow = false;
                selCol = false;
                selectData = !selectData;
            }

        }
    }

    /**
     * Assuming the table is contained in a JScrollPane, scroll to the cell (vRowIndex, vColIndex). <br>
     * The specified cell is guaranteed to be made visible.<br>
     * Every attempt will be made to position the cell in the center of the Viewport. <b>Note:</b> This may not be
     * possible if the row is too close to the top or bottom of the Viewport.
     * <p>
     * It is possible to select the specified cell. The amount of data selected (none, entire row, entire column or a
     * single cell) is dependent on the settings specified by {@link JTable#setColumnSelectionAllowed(boolean)} and
     * {@link JTable#setRowSelectionAllowed(boolean)}.
     * <p>
     * Original code found <a href="http://www.exampledepot.com/egs/javax.swing.table/VisCenter.html">here</a>.
     * <p>
     * 
     * @param table
     *            - The table
     * @param vRowIndex
     *            - The view row index
     * @param vColIndex
     *            - The view column index
     * @param selectCell
     *            - If <code>true</code>, the cell will be selected in accordance with the table's selection policy;
     *            otherwise the selected data will not be changed.
     * @see JTable#convertRowIndexToView(int)
     * @see JTable#convertColumnIndexToView(int)
     */
    public static void displayTableCell(JTable table, int vRowIndex, int vColIndex, boolean selectCell)
    {
        if (!(table.getParent() instanceof JViewport))
        {
            return;
        }

        JViewport viewport = (JViewport) table.getParent();

        /* This rectangle is relative to the table where the
         * northwest corner of cell (0,0) is always (0,0).
         */
        Rectangle rect = table.getCellRect(vRowIndex, vColIndex, true);

        // The location of the view relative to the table
        Rectangle viewRect = viewport.getViewRect();

        /*
         *  Translate the cell location so that it is relative
         *  to the view, assuming the northwest corner of the
         *  view is (0,0).
         */
        rect.setLocation(rect.x
                - viewRect.x, rect.y
                - viewRect.y);

        // Calculate location of rectangle if it were at the center of view
        int centerX = (viewRect.width - rect.width) / 2;
        int centerY = (viewRect.height - rect.height) / 2;

        /*
         *  Fake the location of the cell so that scrollRectToVisible
         *  will move the cell to the center
         */
        if (rect.x < centerX)
        {
            centerX = -centerX;
        }
        if (rect.y < centerY)
        {
            centerY = -centerY;
        }
        rect.translate(centerX, centerY);

        // If desired and allowed, select the appropriate cell
        if (selectCell
                && (table.getRowSelectionAllowed() || table.getColumnSelectionAllowed()))
        {
            // Clear any previous selection
            table.clearSelection();

            table.setRowSelectionInterval(vRowIndex, vRowIndex);
            table.setColumnSelectionInterval(vColIndex, vColIndex);
        }

        // Scroll the area into view.
        viewport.scrollRectToVisible(rect);
    }

    private String addRow(int tableRowIndex)
    {
        String retVal;

        int value = random.nextInt(99999999);
        dtm.addRow(new Object[] {
                value,
                tableRowIndex,
                random.nextInt(99999999),
                random.nextInt(99999999),
                random.nextInt(99999999),
                random.nextInt(99999999),
                random.nextInt(99999999),
                random.nextInt(99999999), });

        retVal = "Row added - value="
                + value + " & tableRowIx=" + tableRowIndex;

        System.out.println(retVal);
        return retVal;
    }

    public static void main(String[] args)
    {
        SwingUtilities.invokeLater(new Runnable()
        {
            @Override
            public void run()
            {
                new JTableScrollToRow().buildGUI();
            }
        });
    }

}

Answer 3

call this method whenever you want to scroll down to the bot of the table. And above problem is solved by using this method.

public void scrolltable()
{
    table.addComponentListener(new ComponentAdapter() {
        public void componentResized(ComponentEvent e) {
            int lastIndex =table.getCellRect(table.getRowCount()-1;
            table.changeSelection(lastIndex, 0,false,false);
        }
    });
}

Answer 4

Why not call fireTableRowsInserted upon updating in your TableModel implementation?

I usally have something like below in my TableModel implementation:

public void addRow (MyDataType valToAdd){
rows.add(valToAdd);
fireTableRowsInserted(rows.size()-1,rows.size()-1);
}