How To Provide More Informative Undo Presentation Names for Document Edits

Question

Hello,
Hopefully, I can state this clearly enough where people will know what I'm talking about.
I'm working on an app that makes use of JTextArea to provide display and editing capabilities for text files. I've registered an UndoableEditListener with the Document underlying the JTextArea, so that I can provide undo/redo capability for all the various edits.
Here's my problem, the edits sent to my listener are of the type AbstractDocument.DefaultDocumentEvent, and so they provide very little information about exactly what sort of event has taken place. IIRC, everything (cut, paste, typing, etc.) shows up as an insert or a removal. I'd like to be able to provide a better presentation name (e.g, "Undo Cut", "Undo Paste", etc.) for my undoable events than is provided by the AbstractDocument.DefaultDocumentEvent , but I'm not sure how exactly to go about this. Do I create my own edits that operate directly on the Document, and avoid the AbstractDocument.DefaultDocumentEvent altogether, or is there some easier way? Anyone have any experience trying to do this? Thanks.
- sixtyten

Answer 1

That's exactly the problem: the information we need isn't available, and there's no way to reconstruct it, so let's have the client tell us what we need to know. What I'm proposing is an UndoManager that requires its client to notify it when an action is about to be performed, and again when the action is finished. Upon receiving the first notification, it creates a CompoundEdit with the presentation name that was provided in the notification. After that, any edits that come in via the undoableEditHappened() method get added to the CompoundEdit instead of directly to the undo stack. When it receives the second notification, the UndoManager ends the CompoundEdit and adds it to the undo stack. Here's a very simplistic example: public class SuperUndoManager extends UndoManager
  // basically just a CompoundEdit with a 'name' attribute.
  private NamedCompoundEdit currentEdit;
  public void beginCompoundEdit(String name)
    currentEdit = new NamedCompoundEdit(name);
  public void endCompoundEdit()
    currentEdit.end();
    addEdit(currentEdit);
  public void undoableEditHappened(UndoableEditEvent evt)
    currentEdit.addEdit(evt.getEdit());
} The biggest problem is getting the clients (i.e., JTextComponents and the Actions defined in their EditorKits) to call these methods without having to do something drastic like replacing them all. I think it can be done (he said with a barely noticeable quaver in his voice).