Form Parts: Creating form method callbacks

http://www.exploreax.com/blog/blog/2014/12/01/form-parts-creating-form-method-callbacks/

1. Create your form and form parts.
2. Add your form part to your main form
3. On your main form create a reference to your form part in the class declaration e.g. Object _part;
4. Create a method on your main form e.g. “registerForChange(Object _part); with the following code:
   public void registerForChange(Object