HOWTO: Determine When a Page Is Done Loading in WebBrowser Ctrl

• Internet Client SDK, versions 4.0, 4.01
• Microsoft Internet Explorer (Programming), versions 4.0, 4.01

SUMMARY

The Internet Explorer WebBrowser control fires the DocumentComplete event when it is finished downloading a Web page. You can create a event handler function in your application for this event. This article describes the steps to take in determining if a the WebBrowser control is finished downloading a Web page.

MORE INFORMATION

The WebBrowser control fires the DocumentComplete event when its ReadyState property is changed to READYSTATE_COMPLETE. This indicates that the WebBrowser control has completed downloading the Web page. Here are some important points regarding this event:

• In the case of a page with no frames, DocumentComplete is fired once after everything is done.
• In case of multiple frames, DocumentComplete gets fired multiple times. Not every frame fires this event, but each frame that fires a DownloadBegin event fires a corresponding DocumentComplete event.
• The DocumentComplete event has a IDispatch* parameter, which is the IDispatch of the frame (shdocvw) for which DocumentComplete is fired.
• The top-level frame fires the DocumentComplete in the end. So, to check if a page is done downloading, you need to check if the IDispatch* parameter is same as the IDispatch of the WebBrowser control.

  For Visual Basic, here is code that performs this check:

        Private Sub WebBrowser1_DocumentComplete(ByVal pDisp As Object,
                                                 URL As Variant)
           If (pDisp Is WebBrowser1.Object) Then
              Debug.Print "Web document is finished downloading"
           End If
        End Sub
  
  

NOTE: These steps are done for you automatically if you add a handler for the DocumentComplete event using the Class Wizard that comes with Visual C++. The only code that you will have to add is what is given in the OnDocumentComplete function:

1. Define the OnDocumentComplete method in the header file for you CView- derived class:

         afx_msg void OnDocumentComplete(LPDISPATCH lpDisp,
                                         VARIANT FAR* URL);
   
   

2. Declare the event sink in the same header file:

         DECLARE_EVENTSINK_MAP()
   

3. In the implementation file (.cpp) for your CView-derived class, implement the event sink map:

         BEGIN_EVENTSINK_MAP(CYourView, CView)
            ON_EVENT(CWBTstView, ID_WEB_BROWSE, 259 /* DocumentComplete */,
                     OnDocumentComplete, VTS_DISPATCH VTS_PVARIANT)
         END_EVENTSINK_MAP()
   
   

4. Implement the OnDocumentComplete method:

         void CWBTstView::OnDocumentComplete(LPDISPATCH lpDisp,
                                             VARIANT FAR* URL)
         {
            IUnknown*  pUnk;
            LPDISPATCH lpWBDisp;
            HRESULT    hr;
   
            pUnk = m_webBrowser.GetControlUnknown();
            ASSERT(pUnk);
   
            hr = pUnk->QueryInterface(IID_IDispatch, (void**)&lpWBDisp);
            ASSERT(SUCCEEDED(hr));
   
            if (lpDisp == lpWBDisp )
            {
               // Top-level Window object, so document has been loaded
               TRACE("Web document is finished downloading\n");
            }
   
           lpWBDisp->Release();
           pUnk->Release();
         }
   
   

The WebBrowser control is hosting a frameset. Within one frame of the frameset, the user clicks on a link that opens a new page in the frame itself and keeps the rest of the frameset intact. The new page could contain multiple frames again. So, there will be multiple DocumentComplete notifications (one for each new frame). But, since the top-level frame has not changed, the final DocumentComplete would be that of the frame that has changed.

If you are interested in checking for the final document complete in this scenario, you could do the following:

• Check if the IDispatch parameter of the DocumentComplete is the same as the IDispatch parameter of first NavigateComplete2 event. Since the first NavigateComplete2 is of the top-level frame and the last DocumentComplete is also of the top-level frame, doing a comparison in such a fashion will tell whether the page is done downloading.

   LPDISPATCH glpDisp = NULL; // global LPDISPATCH, can also
                              // be of class scope

   // NavigateComplete2 event
   void CWebbrDlg::OnNavigateComplete2Explorer1(LPDISPATCH pDisp,
                                                VARIANT FAR* URL)
   {
      // Check if glpDisp is NULL. If NULL, that means it is
      // the top level NavigateComplete2. Save the LPDISPATCH
      if (!glpDisp)
         glpDisp = pDisp;
   }

   void CWebbrDlg::OnDocumentCompleteExplorer1(LPDISPATCH pDisp,
                                               VARIANT FAR* URL)
   {
      if (glpDisp && glpDisp == pDisp)
      {
         // if the LPDISPATCH are same, that means
         // it is the final DocumentComplete. Reset glpDisp
         TRACE("Document is done downloading");
         glpDisp = NULL;
      }
   }

REFERENCES

Internet Client SDK Help (http://www.microsoft.com/msdn/sdk/inetsdk/help/); Search on: "Reusing the WebBrowser Control" in the "Internet Tools and Technologies" section.