Making a refactoring plug-in: How to allow changes?

Hi!

I'm trying my hand at making a refactoring plugin or two for IntelliJ to support our transition to EJB and JPA.  The first one I'm making simply turns static accesses to the current class into accesses to a new instance (except for accesses to constants). From the basic plugin tutorial and various postings here, I have been able to get the plug-in running and find the appropriate references. However, I am stumped at how to actually make any changes -- whenever I try to replace an element, I get

Assertion failed: Write access is allowed inside write-action only (see com.intellij.openapi.application.Application.runWriteAction())

I tried placing it in a write action like this:

            ApplicationManager.getApplication().runWriteAction(new Runnable() {
              public void run() {
                elm.replace(elementFactory.createExpressionFromText("new " + currentClass.getName() + "()", elm));
              }
            });

Then I got

Assertion failed: Undoable actions allowed inside commands only (see com.intellij.openapi.command.CommandProcessor.executeCommand())

Looking at its JavaDocs, I find a gazillion undocumented methods to implement, but in another posting here I notice the WriteCommandAction is supposed to do both for me, so I try that:

            new WriteCommandAction.Simple(project, elm.getContainingFile()) {
              public void run() {
                elm.replace(elementFactory.createExpressionFromText("new " + currentClass.getName() + "()", elm));
              }
            }.run();

But then I get the first exception again.

I also tried adding the "startInWriteAction" method to the action class, no difference.

The changes are made, but they are not undoable. What do I have to do to make an undoable action?  And is there a simple, working example of a refactoring somewhere?

I'm attaching the component code I have (with the WriteCommandAction). I run IntelliJ version 8.0.1 on an Ubuntu 8.10 box.

Thanks in advance,
-Lars Clausen