Question

PageA Navigated to PageB
There is a thread is running for HttpWebRequest.
Back Key is invalid when the Thread is running.
PageB Code:

protected override void OnNavigatedTo(System.Windows.Navigation.NavigationEventArgs e)
    {
        Debug.WriteLine("OnNavigatedTo");
        //base.OnNavigatedTo(e);
        DoWork();
    }

void DoWork()
    {
        t = new Thread(new ThreadStart(() =>
        {
            request = WebRequest.Create("http://www.google.com") as HttpWebRequest;
            request.BeginGetResponse(new AsyncCallback(AsyncBack), request);
        }));
        t.IsBackground = true;
        t.Start();
    }


void AsyncBack(IAsyncResult ias)
    {
        HttpWebRequest req = (HttpWebRequest)ias.AsyncState;
        using (HttpWebResponse res = req.EndGetResponse(ias) as HttpWebResponse)
        {
            this.Dispatcher.BeginInvoke(() =>
            {
                this.PageTitle.Text = res.ContentLength.ToString();
                long length = res.ContentLength;
                for (long i = 0; i < length; i++)
                {
                    //here imitate a long time for working
                    Debug.WriteLine(i);
                    if (i == length)
                    {
                        break;
                    }
                }
                Debug.WriteLine(res.ContentLength);
            });
        }
    }

the Back Key is invalid until Method AsyncBack() is done.
‘Back Key is invalid’ Is that the app is not back to PageA when you touch the Back Key until Method AsyncBack() Done.
Why? Help me?

Answer 1

Why the bloody hell are you wrapping a async request in a custom thread? That doesn’t even remotely make sense.

Then again, your question doesn’t make much sense either, but most likely the error is related to the request is attempting to invoke a operation, via. the dispatcher, on the wrong page.