java - JScrollPane and JList auto scroll

Question

I've got the next code:

    listModel = new DefaultListModel();
    listModel.addElement(dateFormat.format(new Date()) + ": Msg1");
    messageList = new JList(listModel);
    messageList.setLayoutOrientation(JList.VERTICAL);

    messageScrollList = new JScrollPane(messageList);
    messageScrollList.setPreferredSize(new Dimension(500, 200));

    messageScrollList.getVerticalScrollBar().addAdjustmentListener(new AdjustmentListener() {  
        public void adjustmentValueChanged(AdjustmentEvent e) {  
            e.getAdjustable().setValue(e.getAdjustable().getMaximum());  
        }
    }); 

It auto scrolls down. But, if I try to scroll back up to re-read a message, it forces a scroll down. How can I fix this?

Answer 1

When adding a new message, invoke scrollRectToVisible() on the JList using a Rectangle having the same dimensions as your message pane's preferred size. Given a vertical orientation, it may be convenient to make the preferred size of the JScrollPane's JViewport an integral multiple of the message pane's height. See also: How to Use Scroll Panes.

Addendum: This compelling discussion of Text Area Scrolling may be helpful, too.