Webbrowser InvokeScript function is blocking UI thread in Windows Phone 8

Question

I am invoking a Javascript function using Webbrowser in Windows Phone 8.

browserControl.InvokeScript(funtionName, args);

This javascipt function is internally calling a service to fetch the data, during the javascript call i am showing ProgressIndicator.

But i am not able to see ProgressIndicator because javascript call is stopping UI thread.

This problem may be because of Javascript function and my UI thread is running in same thread. So i tried to move my Javascript function call to Background thread, but it failed saying "Invalid cross thread Access"

I am able to see the UI after my ScriptNotify is invoked. Before that i am not able to see my UI

You can see my code snippets below:

Can any one please suggest me how can i overcome this problem?

My progress indicator code:

public void ActivateProgressIndicator(this PhoneApplicationPage currentPage, string progressIndicatorText)
        {
            ProgressIndicator progressIndicator = new ProgressIndicator();
            progressIndicator.Text = progressIndicatorText;
            progressIndicator.IsVisible = true;
            progressIndicator.IsIndeterminate = true;
            SystemTray.SetProgressIndicator(currentPage, progressIndicator);
        }

My JS fucnction is calling a WCF rest service internally, this function call will take 30 seconds 1 minute. And i am JS code to Background thread like below:

ThreadPool.QueueUserWorkItem(o =>
            {
                WebBrowser browserControl = new WebBrowser();
                browserControl.IsScriptEnabled = true;
                browserControl.Navigate(new Uri("/WebAssets/Main.html", UriKind.RelativeOrAbsolute));

                browserControl.InvokeScript("RetrieveAccounts",
                                                         "http://some.service.net/",
                                                         "Plain",
                                                         "arg1",
                                                         "arg2",
                                                         "arg3");
            });

I am getting Invalid cross thread error while i am creating the webbrowser control.

Answer 1

This error is also generally shown when invoking java script method which does some stuff inside webpage like asynchronous call.

In my case it helped to call method this way:

I have taken the WB_LoadCompleted event to fire the invokescript method. You may modify it according to you needs.

    private void WB_LoadCompleted(object sender, NavigationEventArgs e)
    {
        // Make sure the HTML document has loaded before attempting to
        // invoke script of the document page. You could set loadCompleted
        // to true when the LoadCompleted event on the WebBrowser fires.
        ActivateProgressIndicator(this, "hello");
        Dispatcher.BeginInvoke(() =>
            {
                //Give a call to your Browser.InvokeScript here. e.g.
                WB.InvokeScript("execScript", gestureHold);
            });
    }

Hope this helps you. cheers