TextPANE's Y_AXIS preferredSpan not set, but textAREA's is ?

Question

I can do
area = new JTextArea();
area.setText( "Some text" );
view = area.getUI().getRootView( area );
height = view.getPreferredSpan( View.Y_AXIS ) ;and height is set to 16.0. But if I do
pane = new JTextPane();
pane.setText( "Some text" );
view = pane.getUI().getRootView( pane );
height = view.getPreferredSpan( View.Y_AXIS );height is always 0.0. Why is this?
Interestingly,
width = view.getPreferredSpan( View.X_AXIS );does give me a value back , the same in both cases ( 54.0 in my case ).
: jay

Answer 1

Why is this?Check out this demo code:
import javax.swing.*;
import javax.swing.event.*;
import javax.swing.text.*;
public class UTextComponent
     **  Return the current column number at the Caret Position.
     public static int getColumnAtCaret(JTextComponent component)
          int caretPosition = component.getCaretPosition();
          Element root = component.getDocument().getDefaultRootElement();
          int line = root.getElementIndex( caretPosition );
          int lineStart = root.getElement( line ).getStartOffset();
          return caretPosition - lineStart + 1;
          int rowStart = 0;
          try
               rowStart = Utilities.getRowStart(component, component.getCaretPosition());
          catch(BadLocationException ble) {}
          return component.getCaretPosition() - rowStart;
     **  Return the current line number at the Caret position.
     public static int getLineAtCaret(JTextComponent component)
          int caretPosition = component.getCaretPosition();
          Element root = component.getDocument().getDefaultRootElement();
          return root.getElementIndex( caretPosition ) + 1;
     **  Return the number of lines of text.
     public static int getLines(JTextComponent component)
          Element root = component.getDocument().getDefaultRootElement();
          return root.getElementCount();
     **  Position the caret at the start of a line.
     public static void gotoLine(JTextComponent component, int line)
          Element root = component.getDocument().getDefaultRootElement();
          line = Math.max(line, 1);
          line = Math.min(line, root.getElementCount());
          component.setCaretPosition( root.getElement( line - 1 ).getStartOffset() );
          //  The following will position the caret at the start of the first word
          try
               component.setCaretPosition(
                    Utilities.getNextWord(component, component.getCaretPosition()));
          catch(Exception e) {System.out.println(e);}
     **  Return the number of lines of text, including wrapped lines.
     public static int getWrappedLines(JTextPane component)
          int lines = 0;
          View view = component.getUI().getRootView(component).getView(0);
          System.out.println("view: " + (int)view.getPreferredSpan(View.Y_AXIS) );
          int paragraphs = view.getViewCount();
          System.err.println("p: " + paragraphs);
          for (int i = 0; i < paragraphs; i++)
               lines += view.getView(i).getViewCount();
          return lines;
     **  Return the number of lines of text, including wrapped lines.
     public static int getWrappedLines(JTextArea component)
          View view = component.getUI().getRootView(component).getView(0);
          int preferredHeight = (int)view.getPreferredSpan(View.Y_AXIS);
          int lineHeight = component.getFontMetrics( component.getFont() ).getHeight();
          return preferredHeight / lineHeight;
     public static void main(String[] args)
          final JTextPane textComponent = new JTextPane();
//          final JTextArea textComponent = new JTextArea(5, 15);
//          textComponent.setLineWrap( true );
//          textComponent.setWrapStyleWord( true );
//          textComponent.setText("1\n2\n3\n4\n5\n6\n7");
//          textComponent.setEditable(false);
          textComponent.addCaretListener( new CaretListener()
               public void caretUpdate(CaretEvent e)
                    System.out.print
                         "Column/Line : " +
                         UTextComponent.getColumnAtCaret( textComponent ) +
                         "/" +
                         UTextComponent.getLineAtCaret( textComponent ) +
                         ", Lines : " +
                         UTextComponent.getLines( textComponent ) +
                         ", Wrapped Lines : "
                    //  It looks like the View has not yet been updated.
                    //  Add request to end of queue
//                    SwingUtilities.invokeLater( new Runnable()
//                         public void run()
                              System.out.println(
                                   UTextComponent.getWrappedLines( textComponent ) );
          JScrollPane scrollPane = new JScrollPane( textComponent );
          JPanel panel = new JPanel();
          panel.add( new JLabel( "Goto Line:" ) );
          final JTextField gotoField = new JTextField(4);
          panel.add( gotoField );
          gotoField.addActionListener( new java.awt.event.ActionListener()
               public void actionPerformed(java.awt.event.ActionEvent e)
                    UTextComponent.gotoLine(textComponent,
                         Integer.parseInt( gotoField.getText()) );
                    gotoField.setText("");
                    textComponent.requestFocus();
          JFrame frame = new JFrame( "Text Component Utilities" );
          frame.setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE );
          frame.getContentPane().add( scrollPane );
          frame.getContentPane().add(panel, java.awt.BorderLayout.SOUTH);
//          frame.pack();
          frame.setSize(300, 300);
          frame.setVisible(true);
}a) Run the code as is
b) enter a single character, view = 16
c) use enter key to add a new line, view = 16
d) use enter key to add a new line, view = 32
This is inconsistent behaviour. The view should change with each new line
e) use backspace key until you are left with a single character, view = 0 ?
f) use left arrow key, view = 16
Again this is inconsistent
Now remove the comments for the code that uses the SwingUtilities.invokeLater and repeat above tests. This view seems to update normally as far as I can see.
So, I guess the answer to your question is that the view processing for JTextPane is more complicated than it is for JTextArea and some of this processing is added to the end of the event thread when the setText() method is used, so you are getting an old value.
Also, notice how my two methods for getWrappedLines are different for the JTextArea and JTextpane. You would hope/expect that the view methods would return the same values but they didn't. In this case I would consider the JTextPane to be the correct code and the JTextArea inconsistent.