java - JTable horizontal scrollbar based on width of one column

Question

I am running into a problem that has been discussed on here before: getting a JScrollPane containing a JTable to display the horizontal scrollbar as I desire. HERE is a post I tried following, but for some reason it does not seem to work with my situation (I think it is because I've set one of my columns to have a fixed width.

Here is a SSCCE:

import javax.swing.JFrame;
import javax.swing.JScrollPane;
import javax.swing.JTable;
import javax.swing.table.DefaultTableModel;

@SuppressWarnings("serial")
public class TableScrollTest extends JFrame
{
    public TableScrollTest() {

        DefaultTableModel model = new DefaultTableModel(new Object[]{"key", "value"},0);
        model.addRow(new Object[]{"short", "blah"});
        model.addRow(new Object[]{"long", "blah blah blah blah blah blah blah"});

        JTable table = new JTable(model) {
            public boolean getScrollableTracksViewportWidth() {
                return getPreferredSize().width < getParent().getWidth();
            }
        };        
        table.getColumn("key").setPreferredWidth(60);
        table.getColumn("key").setMinWidth(60);
        table.getColumn("key").setMaxWidth(60);
        table.setAutoResizeMode( JTable.AUTO_RESIZE_OFF );

        JScrollPane scrollPane = new JScrollPane( table );
        getContentPane().add( scrollPane );
    }

    public static void main(String[] args) {
        TableScrollTest frame = new TableScrollTest();
        frame.setDefaultCloseOperation( EXIT_ON_CLOSE );
        frame.pack();
        frame.setSize(200, 200);
        frame.setResizable(false);
        frame.setVisible(true);
    }
}

In short, I have a two column table for displaying key/value pairs. The container holding the table is of fixed width, and the first column of the table is also of fixed width (since I know how long all the key names will be). The second column will contain values of varying string length. A horizontal scrollbar should only appear when there are values present which are too long to fit in the width allotted for the column.

Because the second value above has such a long length, the scrollbar should be visible. However, it's not, and everything I have tried has only succeeded in getting it visible always, which is not what I want... I only want it visible if "long" values are present. It seems like the getScrollableTracksViewportWidth() method being overridden in the table constructor checks what the preferred width of the table is... so somehow I need to direct the table to prefer a larger width based on the contents of that second column only... but I'm stumped.

Any ideas?

Answer 1

This is a hackey solution

Basically, what it does is calculates the "preferred" width of all the columns based on the values from all the rows.

It takes into consideration changes to the model as well as changes to the parent container.

Once it's done, it checks to see if the "preferred" width is greater or less than the available space and sets the trackViewportWidth variable accordingly.

You can add in checks for fixed columns (I've not bothered) which would make the process "slightly" faster, but this is going to suffer as you add more columns and rows to the table, as each update is going to require a walk of the entire model.

You could put some kind of cache in, but right about then, I'd be considering fixed width columns ;)

import java.awt.Container;
import java.awt.EventQueue;
import java.awt.event.ComponentAdapter;
import java.awt.event.ComponentEvent;
import javax.swing.JFrame;
import static javax.swing.JFrame.EXIT_ON_CLOSE;
import javax.swing.JScrollPane;
import javax.swing.JTable;
import javax.swing.JViewport;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;
import javax.swing.event.ChangeEvent;
import javax.swing.event.ListSelectionEvent;
import javax.swing.event.TableColumnModelEvent;
import javax.swing.event.TableColumnModelListener;
import javax.swing.event.TableModelEvent;
import javax.swing.table.DefaultTableModel;
import javax.swing.table.TableColumn;
import javax.swing.table.TableColumnModel;

public class TableScrollTest extends JFrame {

    public TableScrollTest() {

        DefaultTableModel model = new DefaultTableModel(new Object[]{"key", "value"}, 0);
        model.addRow(new Object[]{"short", "blah"});
        model.addRow(new Object[]{"long", "blah blah blah blah blah blah blah"});

        JTable table = new JTable(model) {
            private boolean trackViewportWidth = false;
            private boolean inited = false;
            private boolean ignoreUpdates = false;

            @Override
            protected void initializeLocalVars() {
                super.initializeLocalVars();
                inited = true;
                updateColumnWidth();
            }

            @Override
            public void addNotify() {
                super.addNotify();
                updateColumnWidth();
                getParent().addComponentListener(new ComponentAdapter() {
                    @Override
                    public void componentResized(ComponentEvent e) {
                        invalidate();
                    }
                });
            }

            @Override
            public void doLayout() {
                super.doLayout();
                if (!ignoreUpdates) {
                    updateColumnWidth();
                }
                ignoreUpdates = false;
            }

            protected void updateColumnWidth() {
                if (getParent() != null) {
                    int width = 0;
                    for (int col = 0; col < getColumnCount(); col++) {
                        int colWidth = 0;
                        for (int row = 0; row < getRowCount(); row++) {
                            int prefWidth = getCellRenderer(row, col).
                                    getTableCellRendererComponent(this, getValueAt(row, col), false, false, row, col).
                                    getPreferredSize().width;
                            colWidth = Math.max(colWidth, prefWidth + getIntercellSpacing().width);
                        }

                        TableColumn tc = getColumnModel().getColumn(convertColumnIndexToModel(col));
                        tc.setPreferredWidth(colWidth);
                        width += colWidth;
                    }

                    Container parent = getParent();
                    if (parent instanceof JViewport) {
                        parent = parent.getParent();
                    }

                    trackViewportWidth = width < parent.getWidth();
                }
            }

            @Override
            public void tableChanged(TableModelEvent e) {
                super.tableChanged(e);
                if (inited) {
                    updateColumnWidth();
                }
            }

            public boolean getScrollableTracksViewportWidth() {
                return trackViewportWidth;
            }

            @Override
            protected TableColumnModel createDefaultColumnModel() {
                TableColumnModel model = super.createDefaultColumnModel();
                model.addColumnModelListener(new TableColumnModelListener() {
                    @Override
                    public void columnAdded(TableColumnModelEvent e) {
                    }

                    @Override
                    public void columnRemoved(TableColumnModelEvent e) {
                    }

                    @Override
                    public void columnMoved(TableColumnModelEvent e) {
                        if (!ignoreUpdates) {
                            ignoreUpdates = true;
                            updateColumnWidth();
                        }
                    }

                    @Override
                    public void columnMarginChanged(ChangeEvent e) {
                        if (!ignoreUpdates) {
                            ignoreUpdates = true;
                            updateColumnWidth();
                        }
                    }

                    @Override
                    public void columnSelectionChanged(ListSelectionEvent e) {
                    }
                });
                return model;
            }
        };
        table.getColumn("key").setPreferredWidth(60);
//        table.getColumn("key").setMinWidth(60);
//        table.getColumn("key").setMaxWidth(60);
//        table.setAutoResizeMode(JTable.AUTO_RESIZE_NEXT_COLUMN);

        JScrollPane scrollPane = new JScrollPane(table);
        getContentPane().add(scrollPane);
    }

    public static void main(String[] args) {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                    UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
                }

                TableScrollTest frame = new TableScrollTest();
                frame.setDefaultCloseOperation(EXIT_ON_CLOSE);
                frame.pack();
                frame.setSize(200, 200);
                frame.setResizable(true);
                frame.setVisible(true);
            }
        });
    }
}