JList - use a vertical scrollbar instead of horizontal with a vertical wrap orientation?

Question

I'm trying to place a JList inside of a JScrollPane and have it alphabetically list the entries in vertical columns like this:

A D G
B E H
C F 

However when the JList runs out of space to display more entries, I'd like the JScrollPane to scroll only in the vertical direction.

This works when I use VERTICAL_WRAP. However, it seems like when I use vertical wrap I get a horizontal scrollbar and when I use HORIZONTAL_WRAP I get the scrollbar I want, but the items get placed in an order that I don't like. Can I have my cake and eat it too? Here's a simple example of what I'm trying to do.

This is the closest I could get, but I'd like to be able to scroll vertically while maintaining the vertical alphabetical ordering.

public class ScrollListExample {
    static List<String> stringList = new ArrayList<String>();
    static {
        for (int i = 0; i < 500; i++) {
            stringList.add("test" + i);
        }
    }

    public static void main(final String[] args) {
        final JFrame frame = new JFrame();
        final Container contentPane = frame.getContentPane();
        final JList list = new JList(stringList.toArray());
        list.setLayoutOrientation(JList.VERTICAL_WRAP);
        list.setVisibleRowCount(0);
        final JScrollPane scrollPane = new JScrollPane(list);
        contentPane.add(scrollPane);
        frame.setPreferredSize(new Dimension(800, 400));
        frame.pack();
        frame.setVisible(true);
    }
}

One solution I've though of is: If the cell size is known I can create a component listener, and listen for a resize event. When that event is triggered I can calculate the desired row count in order to prevent horizontal scrolling. This just seems like a hack, and I'm not sure how it could work with variable sized text components.

Answer 1

I think your solution is just fine, and not a hack at all. Any built-in feature would have to do basically the same thing anyways.

Here's a modification to your example that does what you want.

public class ScrollListExample {
    static List<String> stringList = new ArrayList<String>();
    static {
        for (int i = 0; i < 500; i++) {
            stringList.add("test" + i);
        }
    }

    public static void main(final String[] args) {
        final JFrame frame = new JFrame();
        final Container contentPane = frame.getContentPane();
        final JList list = new JList(stringList.toArray());
        list.setLayoutOrientation(JList.VERTICAL_WRAP);
        final JScrollPane scrollPane = new JScrollPane(list);
        contentPane.add(scrollPane);
        frame.setPreferredSize(new Dimension(800, 400));
        frame.pack();

        list.addComponentListener(new ComponentAdapter() {
            @Override
            public void componentResized(ComponentEvent e) {
                fixRowCountForVisibleColumns(list);
            }
        });

        fixRowCountForVisibleColumns(list);
        frame.setVisible(true);
    }

    private static void fixRowCountForVisibleColumns(JList list) {
        int nCols = computeVisibleColumnCount(list);
        int nItems = list.getModel().getSize();

        // Compute the number of rows that will result in the desired number of
        // columns
        int nRows = nItems / nCols;
        if (nItems % nCols > 0) nRows++;
        list.setVisibleRowCount(nRows);
    }

    private static int computeVisibleColumnCount(JList list) {
        // It's assumed here that all cells have the same width. This method
        // could be modified if this assumption is false. If there was cell
        // padding, it would have to be accounted for here as well.
        int cellWidth = list.getCellBounds(0, 0).width;
        int width = list.getVisibleRect().width;
        return width / cellWidth;
    }
}