System.UnauthorizedAccessException with text-to-speech in Windows Phone 8

Question

I have the following piece of code for using text to speech feature in Windows Phone 8. I am using ssml, with bookmarks. But when changing any UI element in the Bookmark event called function, raises Unauthorized Exception.

private void Initialise_synthesizer()
        {
            this.synthesizer = new SpeechSynthesizer();

            synthesizer.BookmarkReached += new TypedEventHandler<SpeechSynthesizer, SpeechBookmarkReachedEventArgs>
                (BookmarkReached);
        }

void BookmarkReached(object sender, SpeechBookmarkReachedEventArgs e)
        {
            Debugger.Log(1, "Info", e.Bookmark + " mark reached\n");

            switch (e.Bookmark)
            {
                case "START":
                    cur = start;
                    break;
                case "LINE_BREAK":
                    cur++;
                    break;
                }
**error here**  t1.Text = cur.ToString();
            }

But on running it gives the following error

A first chance exception of type 'System.UnauthorizedAccessException' occurred in System.Windows.ni.dll
An exception of type 'System.UnauthorizedAccessException' occurred in System.Windows.ni.dll and wasn't handled before a managed/native boundary
Invalid cross-thread access.

Any idea how to fix this error, or any work around.

Answer 1

Just got the answer.

Since the synthesizer.SpeakSsmlAsync() is an async function, to perform UI operations Dispatcher has to be used, something like this -

Dispatcher.BeginInvoke(() =>
                t1.Text = cur.ToString());

Answer 2

It's pretty much unrelated to the speech recognition. It seems that it's related to accessing elements which are on the UI thread from a different thread.

Try this:

Dispatcher.BeginInvoke(() => 
    {
        t1.Text = cur.ToString();
    }
);

Answer 3

From AppManifest.xml turn on capability ID_CAP_SPEECH_RECOGNITION.