JScrollPane, JTextPane, Weird scrolling happening

Question

The code below shows the problem I am having: In short, I have a textPane in a scrollPane but when I try to getViewPort.setViewPosition(0,0); then the scroll pane briefly flashes to position 0,0 then re positions itself to display the bottom of the text pane. It is driving me wild! If I removed the InsertString function call used on the Document of the textPane, then it works as I thought it should (apart from an initial glitch where the slider bar is placed near the top...- see example)
in the example I have a 'tall' JTextPane (ie, lot's of linefeeds) with a red panel all in a JPanel which inturn lies in a JScrollPane. Click on the 'Force Update' button to force the Text pane to be updated (in my real java class, there is other stuff to change the values of the textpane) and to set the display position to 0,0. Notice how the slider button flashes to the top of the vertical bar then returns to the bottom. If you cick on the 'toggle InsetString Active' button, then the code to Insert the String to the textArea is by-passed. Now clicking on the 'Force Update' button (after the initial glitch) does send the view to the top of the Jpanel(which now contains an empty textarea and a red panel).
Can anyone give any clues as to what is causing the Scroll pane to redraw to the bottom of the panel? (and what is causing the glitch after the toggle InsertString button is pressed?)
I have tried it on JDK 1.3.1 and 1.4 and scoured the groups for similar problems but found none. Lots have people had prblems getting the JScrollpane to the bottom of the textpane but I can't seem to stop it going down!
I'd appreciate any help as I'm quickly going bald....
Marc
code begins....
-------------------------cut here--------------------------
import javax.swing.*;
import java.awt.*; //for layout managers
import java.awt.event.*; //for action and window events
import javax.swing.text.*;
public class WierdScroll extends JFrame
ScrollPane scrollPane = null;
JButton button = null;
JButton b2 = null;
JPanel screen = null;
// below is the style to be associated with the textpane
static private SimpleAttributeSet normalStyle = new SimpleAttributeSet(StyleContext.getDefaultStyleContext().getStyle(StyleContext.DEFAULT_STYLE));
static
StyleConstants.setFontFamily(normalStyle, "Courier");
StyleConstants.setFontSize(normalStyle, 12);
public WierdScroll()
super("Wierd Scrolling \'feature\'");
// create and setup the components
screen = new JPanel();
scrollPane = new ScrollPane();
scrollPane.setVerticalScrollBarPolicy(
JScrollPane.VERTICAL_SCROLLBAR_ALWAYS);
scrollPane.setPreferredSize(new Dimension(250, 155));
scrollPane.setMinimumSize(new Dimension(10, 10));
scrollPane.updateConstraintView();
button = new JButton("Force update");
button.addActionListener(new java.awt.event.ActionListener()
public void actionPerformed(ActionEvent e)
scrollPane.updateConstraintView();
b2 = new JButton("toggle InsertString Active");
b2.addActionListener(new java.awt.event.ActionListener()
public void actionPerformed(ActionEvent e)
JButton b = (JButton) e.getSource();
scrollPane.allowInsertString = !scrollPane.allowInsertString;
scrollPane.updateConstraintView();
// add the component to the frame
screen.add(scrollPane);
screen.add(button);
screen.add(b2);
getContentPane().add(screen);
public static void main(String[] args) {
JFrame frame = new WierdScroll();
frame.addWindowListener(new WindowAdapter() {
public void windowClosing(WindowEvent e) {
System.exit(0);
frame.pack();
frame.setVisible(true);
// this extended class is the scrollpane. The problem occurrs when the doc.insertString function is called;
// When insertString is called, the scroll pane flicks to the bottom of the scroll view but when insertString
// is not called then the setViewPostion works OK....
public class ScrollPane extends JScrollPane
public JPanel panel;
public JTextPane margin;
public boolean allowInsertString = true;
/** Creates a new instance of ConstraintView */
public ScrollPane()
// create the pane
margin = new JTextPane();
// create the label
JPanel jp = new JPanel();
jp.setBackground(Color.red);
jp.setPreferredSize(new Dimension(500,500));
panel = new JPanel();
panel.setBackground(Color.white);
// add the label and pane to the panel
panel.add(margin);
panel.add(jp);
// set the scroll voew to be the panel
setViewportView(panel);
public void updateConstraintView()
// if doc has stuff in it, then clear contents
Document doc = margin.getDocument();
if (doc.getLength() > 0)
try
doc.remove(0, doc.getLength());
catch (BadLocationException ble) {}
// the allowInsertString is toggled via button on screen to stop insertString call
if (allowInsertString)
try {
doc.insertString(0, "1\n2\n3\n4\n5\n6\n7\n8\n9\n0\n1\n2\n3\n4\n5\n6\n7\n8\n9\n0\n1\n2\n3\n4\n5\n6\n7\n8\n9\n0\n1\n2\n3\n4\n5\n6\n7\n8\n9\n0\n1\n2\n3\n4\n5\n6\n7\n8\n9\n0\n1\n2\n3\n4\n5\n6\n7\n8\n9\n0\n1\n2\n3\n4\n5\n6\n7\n8\n9\n0\n1\n2\n3\n4\n5\n6\n7\n8\n9\n0\n", normalStyle);
catch (BadLocationException ble) {}
// set viewport so that it scrolls to top
getViewport().setViewPosition(new Point(0,0));

Answer 1

Cheers!
using the setCaretPosition() of the JTextPane instead of the getViewport().setViewPosition(new Point(0,0)) method of the JScrollPane works a treat.
But I would have thought that the scroll pane should have 'complete' control (unless specified by programmer) of what it displays. It seems strange to have a component of a scrollpane dictate to the scrollpane what it should show...
Thanks for your assistance.
On a different note, has anyone noticed that the word 'c l a s s' has become cl***?? Is this a victim of sun's new swear filter to go with the new site look?