[CS4Win] InDesign hangs when open alert dialog on doc close

Question

Hi,  When the user is closing a document, I would like to perform some logic and open an alert dialog in case of error . So I attached a doc listener to the IID_IWINDOW protocol on the Document Presentation for the doc.   When the observer receives the kLayoutWidgetBoss on that protocol, InDesign hangs at the point when the plug-in tries to open the alert box.
Here is the gist of it ...
void  MyDocObserver::Update(const ClassID& theChange, ISubject* theSubject, const PMIID& protocol, void* changedBy)
   switch (protocol.Get())
     case IID_IPRESENTATIONLIST:     
       if(theChange == kOpenLayoutCmdBoss)  {
         IDocumentPresentation* frontDocPresentation = Utils()->GetActiveDocumentPresentation();
         InterfacePtr wsubject(frontDocPresentation, IID_ISUBJECT);
         wsubject->AttachObserver(ISubject::kRegularAttachment, this, IID_IWINDOW, IID_ILAYERSETDOCOBSERVER);
      break;
    case IID_IWINDOW:
      if(theChange == kLayoutWidgetBoss)  // also tried kCloseWinCmdBoss
         // processing
         if(failed)
           CAlert::WarningAlert(kSomeTextKey);  // INDESIGN HANGS HERE.
         // detach observer on IID_IWINDOW
      break;
   default:
      break;
I have also tried to listen to the kPresentationClosedMessage on the IID_IPRESENTIONLIST protocol, without going through the trouble of attaching /detaching listeners on the IID_IWNDOW protocol, but it produces the same result.
I couldn't use the DocResponder for the BeforeClose message, because the processing requires the document still open in the front window. This same piece of code works in CS3, and also in CS4 on Mac, but it failed in CS4 on Windows.
Am I missing something obvious?
Thanks,
Mingjian Song

Answer 1

Hi Markus, having spare time? 
Mingjian, there is a completely different mechanism - search the forum for DocFileHandler.
When you use that approach, please apply full chaining so that other plugins also have their chance.
Dirk