problem with nsIWebProgress::addProgressListener

[Nanjun Hu]

I am making an XPCOM component, which implements nsIObserver and nsIWebProgressListener. The component registers for the xpcom-startup category. In the nsIObserver::Observe method, I called my AddProgressListener method, in which I got a reference to nsIWebProgress through GetServiceByContractID. But the call to progress->AddProgressListener fails. Basiclly, I am trying the code in the http://lxr.mozilla.org/mozilla/source/uriloader/prefetch/nsPrefetchService.cpp#305 (thanks Darin). I can't see the difference between my code to add the progressListener and the code of PrefetchService does the same thing. But the progress->AddProgressListener method just fails. Could anyone tell me where I am wrong? How to add the webProgressListener sucessfully? Thank you very much for your guys' help.

 

NS_IMETHODIMP
mybho::Observe(nsISupports *aSubject, const char *aTopic, const PRUnichar *aData)                
{
 if (!strcmp(aTopic, NS_XPCOM_STARTUP_OBSERVER_ID)){
    AddProgressListener();
 }

 return NS_OK;
}

 

void mybho::AddProgressListener()
{
    nsresult rv;
   // Register as an observer for the document loader
   nsCOMPtr<nsIServiceManager> servman;
   NS_GetServiceManager(getter_AddRefs(servman));

   nsCOMPtr<nsIWebProgress> progress;
   if (servman)
     servman->GetServiceByContractID("@mozilla.org/docloaderservice;1",
                                                        NS_GET_IID(nsIWebProgress),
                                                        getter_AddRefs(progress));

  if (progress){

    // reach here
     rv = progress->AddProgressListener(this,  nsIWebProgress::NOTIFY_STATE_DOCUMENT);

 }
 
 //test
 if (NS_OK == rv){

   //this doesn't work
  fopen("c:\\temp\\ok.txt", "w");
 }

 if (NS_FAILED(rv)){

  //reach here
   fopen("c:\\temp\\bad.txt", "w");
 }
 //test
}

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