JTextCompoent.modelToView(int pos) where pos is offset in Document Model
returns null instead of a rectangle. thus cannot use JViewPort.scrollRectToVisible(rectangle) to scroll to view port to position
pos.


model to view retruns null in such a case shown
by the sample code. The sample code extends JTextArea
and sets the Doc Model to Plain Document. a file is open
and read into the JTextArea via the OpenFile method
call. The call is made to mdoelToView(int pos)
where pos is the begining offset of line 90. The
call returns null every time, thogh the pos is a
valid offset within the document. Consequently the call to
JViewPort.ScrollRectToVisible(rectangle) fails.

1. Compile with JDK115 on solaris 2.5 Sparc
with Swing 1.0.2 and watch the following trace info.

doc length: 3554
modelToView returns null
are we focusing yet? true
caret is at: 3014

2. Since modelToView call returns Null i than
attempt to set the Cursor to the begining of line
90. This works on solaris sparc but completely fails on
solaris x86. Since the cursor is now set to a
position outside the view port on as soon as I start
entering keys the view port jumps to the show
the cursor position, but the view port should have moved
before i started typing. As mentioned in
...swing.text.DefaultCaret.java which implements the
setCaretPosition call and claims that it makes sure
the caret is within the visible region of the view.

Here is the code.

import java.awt.*;
import java.beans.*;
import java.net.*;
import java.awt.event.*;
import java.io.*;
import java.util.*;
import com.sun.java.swing.*;
import com.sun.java.swing.text.*;
import com.sun.java.swing.plaf.*;
import com.sun.java.swing.event.*;

public class ScrollRectTest extends JTextArea {

ScrollRectTest () {
setDocument(new PlainDocument());

     }

public void openFile(String fileName) {

        File f = new File(fileName);

try {
Reader in = new FileReader(f);
        read(in, f);
        } catch (IOException e) {
                System.err.println(e.toString());
          }
  }

   public static void main(String[] args) {

int offset = 0;
Rectangle rect = new Rectangle();

       ScrollRectTest editor = new ScrollRectTest();
       JScrollPane scroller = new JScrollPane();

       JViewport vp = scroller.getViewport();
       vp.add(editor);
vp.setBackingStoreEnabled(true);

        JPanel panel = new JPanel();
        panel.setLayout(new BorderLayout());
        panel.add("Center", scroller);


       JFrame f = new JFrame("JavaEditorKit: ");
       f.getContentPane().setLayout(new BorderLayout());
       f.getContentPane().add("Center", panel);
       f.addWindowListener(new WindowAdapter() {
public void windowClosing(WindowEvent e) {System.exit(0);}
});

       f.pack();
       f.setSize(600, 600);
       f.setVisible(true);

       editor.setBackground(Color.white);
       editor.setFont(new Font("Courier", 0, 12));
       editor.openFile("NOTES.txt");
       editor.setEditable(true);

Document doc=editor.getDocument();
System.out.println("doc length: "+doc.getLength());


/* get the start offset at line 90 */
try {
offset = editor.getLineStartOffset(90);
} catch (BadLocationException ex) {
                ex.printStackTrace();
}

try {
rect = editor.modelToView(offset);
} catch (BadLocationException ex) {
ex.printStackTrace();
}

System.out.println("modelToView returns " + rect);

if ( rect != null)
{
vp.scrollRectToVisible(rect);
System.out.println("rect is: "+rect.x +" and " + rect.y);
}
else
{
//Ok. set the caret postion to see if we scroll
editor.setRequestFocusEnabled(true);
editor.requestFocus();
System.out.println("are we focusing yet? "+editor.isRequestFocusEnabled());
editor.setCaretPosition(offset);
System.out.println("caret is at: "+editor.getCaretPosition());
}
   }
}