Thursday, September 25, 2008

Calling javascript from ActiveX component.

Recently I was trying to call javascript functions in a web page from an embeded activex component i'm working on (The same way a flex developer do using ExternalInterface).

Problems facing this kind of action:

The problem in MFC is that life is not easy like Flex in this specific point. You have to deal with alot of COM interfaces to get what you want. So my problem was as follows.

  1. I should get a reference to the window that the ActiveX control is embeded in (in my case, it will be an IE tab).

  2. Try to get an interface from this window to an html container to be able to access html and javascript.

  3. find the javascript function you want to call.

  4. formulate the parameters in the way that suits the Interface.

    1. Starting a normal ActiveX control application using the app wizzard, leaving all the default settings.

    2. in the ActiveXCtrl class added a CComPtr which i will be using to access the javascript functions inside the web page.

    3. Added a new method I called it FindMainWindow() and called it in the OnDraw()method.

    4. the code of FindMainWindow()Is as follows.
      void FindMainWindow()
      LPOLECLIENTSITE lpClientSite = NULL;
      lpClientSite = GetClientSite();
      CComPtr<IServiceProvider> serviceProvider(0);
      CComPtr<IWebBrowserApp> webBrowserApp(0);
      CComPtr<IWebBrowser2> webBrowser(0);
      CComPtr<IDispatch> dispatch(0);
      if(SUCCEEDED(lpClientSite->QueryInterface(IID_IServiceProvider,(void**)&serviceProvider))) {
      { }
      LOG(_T("Found Html Document:"));

      As you can see here, I needed to get first an IServiceProvider interface from theIOLEClientSite i got by calling GetClientSite().
      The following link in the msdn documentation says in the remarks section that The IWebBrowser2 interface derives from IDispatch indirectly. IWebBrowser2 derives from IWebBrowserApp, which in turn derives from IWebBrowser, which finally derives from IDispatch. So i had to get an IWebBrowserApp interface then IWebBrowser2. Finally getting an IDispatch interface to get the IHTMLDocumtne2 from it.

    5. Here we start to call a javascript methods within the IHTMLDocument2 interface we have got earlier. we call get_script(IDispatch*) to get the script object. The following code demonstrate how to get the id of a given javascript function name, formulating the parameters and invoking the function.
      CComPtr spScript;
      return false;
      CComBSTR bstrMember(function);
      DISPID dispid = NULL;
      HRESULT hr = spScript->GetIDsOfNames(IID_NULL,&bstrMember,1,LOCALE_SYSTEM_DEFAULT,&dispid);

      return false;

      CStringArray paramArray;
      const int arraySize = paramArray.GetSize();
      DISPPARAMS dispparams;
      memset(&dispparams, 0, sizeof dispparams);
      dispparams.cArgs = arraySize;
      dispparams.rgvarg = new VARIANT[dispparams.cArgs];

      for( int i = 0; i < arraySize; i++)
      CComBSTR bstr = paramArray.GetAt(arraySize - 1 - i); // back reading
      dispparams.rgvarg[i].vt = VT_BSTR;
      dispparams.cNamedArgs = 0;
      EXCEPINFO excepInfo;
      memset(&excepInfo, 0, sizeof excepInfo);
      CComVariant vaResult;
      UINT nArgErr = (UINT)-1; // initialize to invalid arg

      hr = spScript->Invoke(dispid,IID_NULL,0,DISPATCH_METHOD,&dispparams,&vaResult,&excepInfo,&nArgErr);
      return false;
      *pVarResult = vaResult;
      return true;

  5. Finally call the javascript and cross fingers!


    Here is what i succeeded in after 5 hours of searching and reading and debugging code.

    I have simplified this example as it was a testing to show that javascript is called successfully.
    The detailed example on calling javascript from IHTMLDocument2 can be found in this link