RE: Detecting whether or not the user changed anything on a form

[Hannum, Daniel]

Thanks very much

You have " addValueChangeListener(this)". I assume instead I should be
adding the VCL class as a listener, not the phase listener. Similar, you
have the assignableFrom code which doesn't compile. The goal there is
just to check if there are any VCL's of thar particular type type
assigned to this class, right?

I'm pretty sure I understand what you're doing here, and I like it. Just
clarifying.

Thanks.

-----Original Message-----
From: Andrew Robinson [mailto:[EMAIL PROTECTED] 
Sent: Friday, July 13, 2007 12:24 PM
To: MyFaces Discussion
Subject: Re: Detecting whether or not the user changed anything on a
form

> I think this will do unless you can think of a way to avoid having to
add the VCL tag to every component.

This is when you may consider a PhaseListener, or component binding.
You could surf the entire component tree recursively, and add your VCL
to all components implementing EditableValueHolder.

public class VCLPhaseListener implement PhaseListener {
  public void afterPhase(PhaseEvent event) { }

        public void beforePhase(PhaseEvent event) {
    UIViewRoot viewRoot = event.getFacesContext().getViewRoot();
    if (viewRoot != null) {
      addVCL(viewRoot);
    }
  }

        public PhaseId getPhaseId() {
    return PhaseId.PROCESS_VALIDATIONS;
  }

  private void addVCL(UIComponent component) {
    if (component instanceof EditableValueHolder &&
      !hasVCL((EditableValueHolder)component)) {
      ((EditableValueHolder)component).addValueChangeListener(this);
    }
    for (Iterator iter = component.getFacetsAndChildren();
iter.hasNext(); ) {
      addVCL(iter.next());
    }
  }

  private boolean hasVCL(EditableValueHolder holder) {
    for (ValueChangeListener listener :
holder.getValueChangeListeners()) {
      if (VCLPhaseListener.class.assignableFrom(listener.getClass())) {
        return true;
      }
    }
    return false;
  }

  ... VCL Code
}

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