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How To Determine When a Page Is Done Loading in WebBrowser Control

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This article was written about products for which Microsoft no longer offers support. Therefore, this article is offered "as is" and will no longer be updated.
The Internet Explorer WebBrowser control fires the DocumentComplete eventwhen it is finished downloading a Web page. You can create a event handlerfunction in your application for this event. This article describes thesteps to take in determining if a the WebBrowser control is finisheddownloading a Web page.
More information
The WebBrowser control fires the DocumentComplete event when its ReadyStateproperty is changed to READYSTATE_COMPLETE. This indicates that theWebBrowser control has completed downloading the Web page. Here are someimportant 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 IfEnd Sub					
To handle the DocumentComplete event in Visual C++ and determine if thedownload of the Web page is complete, follow these steps.

Note that the steps you follow depend on the way you use the WebBrowser control.
  • If you are creating the WebBrowser control in a CWnd/CView object, youmust follow steps 1 to 4.
  • If you are creating the WebBrowser control in a CDialog/CFormView object,only need to follow step 4.
  • If you are using the CHtmlView class provided with Visual C++ 6.0,override CHtmlView::DocumentComplete() and follow step 4, using them_pBrowserApp member of the CHtmlView class to access the WebBrowser control.
  1. Define the OnDocumentComplete method in the header file for your CWnd/CView-derived class:
    afx_msg void OnDocumentComplete(LPDISPATCH lpDisp,                                VARIANT FAR* URL);					
  2. Declare the event sink in the same header file:
  3. In the implementation file (.cpp) for your CWnd/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();}					
This approach works when the WebBrowser control navigates to a page thatchanges the top-level frame. Say if the navigation occurs within a frameitself, then the final DocumentComplete that is fired is that of the frameand not the top-level frame. For example, consider the following scenario.

The WebBrowser control is hosting a frameset. Within one frame of theframeset, the user clicks on a link that opens a new page in the frameitself and keeps the rest of the frameset intact. The new page couldcontain multiple frames again. So, there will be multiple DocumentCompletenotifications (one for each new frame). But, since the top-level frame hasnot changed, the final DocumentComplete would be that of the frame that haschanged.

If you are interested in checking for the final document complete in thisscenario, 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.
Here is some sample C++ code:
LPDISPATCH glpDisp = NULL; // global LPDISPATCH, can also                           // be of class scope// NavigateComplete2 eventvoid 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;   }}				

Article ID: 180366 - Last Review: 06/22/2014 18:46:00 - Revision: 4.0

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