BackKey not working when a Thread is running. Why? - windows-phone-7

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.

Answer 2

In your code you block UI thread for a long time, so you can't navigate page back, because it happens also on UI thread, put into Dispatcher only code that can't be executed not on UI.
void DoWork()
{
HttpWebRequest request = WebRequest.Create("http://www.googl.com") as HttpWebRequest;
request.BeginGetResponse(new AsyncCallback(AsyncBack), request);
}
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++)
{
long i_ = i;
//here imitate a long time for working
Thread.Sleep(10);
this.Dispatcher.BeginInvoke(() =>
{
this.PageTitle.Text = i_.ToString();
});
if (i == length)
{
break;
}
}
Debug.WriteLine(res.ContentLength);
}
}