Custom CompaundEdit for improved Undo Support

Question

Hi,
how can i create a custom CompoundEdit for my JTextPane? By default every change on my Document is one Edit, so that everytime i press a Key, an Edit is created and put into my UndoManager, but i want to undo more than one character once i pressed my Undo Button, like MSWord does.
I really dont know where to start?
It would be great if someone can help me.
kbj

Answer 1

I think the original request is for the ability to undo multple groups of edits. For example:
1) enter 'abc'
2) go back to start of document and enter '123'
3) undo should remove '123'
4) undo again should remove 'abc'
(the default undo would remove 3, 2, 1, c, b, a)
Stas, the solution you provided removes '123abc' when the first undo is invoked.
Assuming, my understanding of the question is what the user wants, the following code works. My approach is to build a compound edit with individual edits that differ from the previous offset by only 1. When the offset is greater than 1, the compound edit is 'ended' and added to the UndoManager.
The problem with this approach is that the compound edit is always considered 'inProgress' and the canUndo() method always returns false. Using suggestions found in this thread I then attempted to create MyCompoundEdit and override the addEdit() method so I could end() the compound edit as soon as it is created. Now, the canUndo() method works however, all edits are merged into 1 when an undo is done.
Maybe, my approach will give some ideas to others who might be able to solve the problem.
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.text.*;
import javax.swing.event.*;
import javax.swing.undo.*;
public class CompoundUndoManager extends UndoManager implements     UndoableEditListener
     public CompoundEdit compoundEdit;
     private JTextComponent editor;
     private int lastOffset;
     public CompoundUndoManager(JTextComponent editor)
          this.editor = editor;
          editor.getDocument().addUndoableEditListener( this );
     public void undoableEditHappened(UndoableEditEvent e)
          // Start a new compound edit
          if (compoundEdit == null)
               compoundEdit = startCompoundEdit( e.getEdit() );
               return;
          //  Check for an incremental edit
          if (editor.getCaretPosition() == lastOffset + 1)
               compoundEdit.addEdit( e.getEdit() );
               lastOffset++;
               return;
          //  Not incremental edit, start a new one
          compoundEdit.end();
          compoundEdit = startCompoundEdit( e.getEdit() );
     private CompoundEdit startCompoundEdit(UndoableEdit anEdit)
          lastOffset = editor.getCaretPosition();
          compoundEdit = new CompoundEdit();
          // Uncomment the following two lines to use MyCompoundEdit
          // unfortunately all edits are merged back into one
//          compoundEdit = new MyCompoundEdit();
//          compoundEdit.end();
          compoundEdit.addEdit( anEdit );
          addEdit( compoundEdit );
          return compoundEdit;
     class MyCompoundEdit extends CompoundEdit
          public boolean addEdit(UndoableEdit anEdit)
               edits.addElement(anEdit);
               return true;
     public static void main(String[] args)
          final JTextPane textPane = new JTextPane();
          textPane.setPreferredSize( new Dimension(200, 200) );
          final CompoundUndoManager undoManager = new CompoundUndoManager( textPane );
          JPanel panel = new JPanel();
          panel.setLayout( new BorderLayout() );
          panel.add( textPane, BorderLayout.CENTER );
          JPanel buttons = new JPanel();
          panel.add(buttons, BorderLayout.SOUTH);
          JButton undo = new JButton( "Undo" );
          undo.addActionListener( new ActionListener()
               public void actionPerformed(ActionEvent e)
                    try
                         System.out.println( undoManager.canUndo() );
                         undoManager.compoundEdit.end();
                         System.out.println( undoManager.canUndo() );
                         undoManager.undo();
                         textPane.requestFocus();
                    catch (CannotUndoException ex)
                         System.out.println("Unable to undo: " + ex);
          buttons.add( undo );
          JButton redo = new JButton( "Redo" );
          redo.addActionListener( new ActionListener()
               public void actionPerformed(ActionEvent e)
                    try
                         undoManager.redo();
                         textPane.requestFocus();
                    catch (CannotRedoException ex)
                         System.out.println("Unable to redo: " + ex);
          buttons.add( redo );
          JFrame frame = new JFrame("Compound Edit");
          frame.setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE );
          frame.getContentPane().add( panel );
          frame.pack();
          frame.setVisible(true);
}