Customizing Undo for Text Editor

Question

Hi,
After some effort, I finally made the undo action on the menu to work. But all it does it add or remove the last action that was performed. For instance, if I enter "abc" in the text area and I undo it, it would be "ab". What I want from the editor is to bring back whatever I've entered before pressing "Backspace" or "del" button. Just like Windows Notepad.
For the implimentaion, I have this method:
output.getDocument().addUndoableEditListener(new UndoableEditListener() {
public void undoableEditHappened(UndoableEditEvent e) {
     undoManager.addEdit(e.getEdit()) ;
     updateButtons();
I know I have to alter the above code somehow, but I'm not sure what am I supposed to do with it.
Any help is appreciated.

Answer 1

Here is a class I called CompoundUndoManager, which may be what you are looking for:
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 );
     **  Whenever an UndoableEdit happens the edit will either be absorbed
     **  by the current compound edit or a new compound edit will be started
     public void undoableEditHappened(UndoableEditEvent e)
          //  Start a new compound edit
          if (compoundEdit == null)
               compoundEdit = startCompoundEdit( e.getEdit() );
               return;
          //  Check for an incremental edit, backspace or attribute change
          AbstractDocument.DefaultDocumentEvent event =
               (AbstractDocument.DefaultDocumentEvent)e.getEdit();
          System.out.println(event.getLength());
          int diff = editor.getCaretPosition() - lastOffset;
          if (Math.abs(diff) == 1
          ||  event.getType().equals(DocumentEvent.EventType.CHANGE) )
               compoundEdit.addEdit( e.getEdit() );
               lastOffset += diff;
               return;
          //  Not incremental edit, end previous edit and start a new one
          compoundEdit.end();
          compoundEdit = startCompoundEdit( e.getEdit() );
     **  Each CompoundEdit will store a group of related incremental edits
     **  (ie. each character typed or backspaced is an incremental edit)
     private CompoundEdit startCompoundEdit(UndoableEdit anEdit)
          //  Track the starting offset of this compound edit
          lastOffset = editor.getCaretPosition();
          //  The compound edit is used to store incremental edits
          compoundEdit = new MyCompoundEdit();
          compoundEdit.addEdit( anEdit );
          //  The compound edit is added to the UndoManager. All incremental
          //  edits stored in the compound edit will be undone/redone at once
          addEdit( compoundEdit );
          return compoundEdit;
     class MyCompoundEdit extends CompoundEdit
          public boolean isInProgress()
               //  in order for the canUndo() and canRedo() methods to work
               //  assume that the compound edit is never in progress
               return false;
          public void undo() throws CannotUndoException
               //  End the edit so future edits don't get absorbed by this edit
               if (compoundEdit != null)
                    compoundEdit.end();
               super.undo();
               //  Always start a new compound edit after an undo
               compoundEdit = null;
     public static void main(String[] args)
          final JTextPane textPane = new JTextPane();
          textPane.setPreferredSize( new Dimension(200, 200) );
          //  Comment out this code when not using SyntaxDocument class
          //  http://www.discoverteenergy.com/files/SyntaxDocument.java
          EditorKit editorKit = new StyledEditorKit()
               public Document createDefaultDocument()
                    return new SyntaxDocument();
          textPane.setEditorKit(editorKit);
          final CompoundUndoManager undoManager = new CompoundUndoManager( textPane );
          JPanel panel = new JPanel();
          panel.setLayout( new BorderLayout() );
          panel.add( new JScrollPane(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
                         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);
}