Question

I have a JTable which is created with the use of an EventTableModel and is in a JScrollPane. The EventTableModel takes live updates from an eventList and displays the result in the table. As new results come into the table and the new piece of information is displayed at the top of the table.

However, what I want to be able to do is freeze the table to show what is currently displayed when I press a button called ‘Lock Table’. This button should have the same effect as the eclipse console ‘Scroll Lock’, therefore as new items appear the current items should remain on the screen and not be pushed off as new items appear. But new items should still be added just not automatically scrolled to.

Does anyone know how I can try achieve this functionality. So that as update come in, the data that is on the table is not forced off screen, therefore focuses remain on the current data when the check box is pressed.

Thanks for any help.
Michael

Answer 1

Basic procedure (for inserting above the current display area)

• install a TableModelListener on the table’s model
• on enable lock: note the number of rows below the current visible rectangle
• on receiving inserts while locked, scroll so that the number of rows below are kept constant

some working code (using JXTable, as it has convenience method for scrolling, for a core table simply do the calculations yourself 🙂

public static class ScrollLock {
    private JXTable table;
    private boolean blocked;
    private int rowsBelow;

    public ScrollLock(JXTable table) {
        this.table = table;
        table.getModel().addTableModelListener(getTableModelListener());
    }

    private TableModelListener getTableModelListener() {
        TableModelListener l = new TableModelListener() {

            @Override
            public void tableChanged(TableModelEvent e) {
                if (!blocked) return;
                if (e.getType() == TableModelEvent.INSERT) {
                    updateInsert(e.getFirstRow(), e.getLastRow());
                }
            }

        };
        return l;
    }

    protected void updateInsert(int firstRow, int lastRow) {
        // PENDING: assumption is that insert always above
        // need additional logic for other cases
        SwingUtilities.invokeLater(new Runnable() {
            @Override
            public void run() {
                Rectangle r = table.getVisibleRect();
                int row =table.rowAtPoint(new Point(0, r.y + r.height));
                int lastVisible = table.getRowCount() - rowsBelow;
                table.scrollRowToVisible(lastVisible);
            }
        });
    }

    public void block() {
        Rectangle viewRect = table.getVisibleRect();
        int lastVisibleRow = table.rowAtPoint(new Point(0, viewRect.y + viewRect.height));
        rowsBelow = table.getRowCount() - lastVisibleRow;
        blocked = true;
    }

    public void unblock() {
        blocked = false;
        rowsBelow = -1;
    }

}