WP7 WebClient DownloadStringAsync and Map - windows-phone-7

Question

I'm using WebClient object in to poll some data from server.
It's working good and it's updating text block fine. Till I don't use map on same Page. When I add a map, only one request get completed and data is retrieved only once.
This is the code for getting messages:
public MessagesPage()
{
InitializeComponent();
new System.Threading.Timer(messagePolling, null, 0, 5000); // every 5 seconds
}
void messagePolling(object state)
{
getMessages(Const.GET_MESSAGES_URL + uuid);
}
private void getMessages(string uri)
{
WebClient webClient = new WebClient();
webClient.DownloadStringAsync(new Uri(uri));
webClient.DownloadStringCompleted += new DownloadStringCompletedEventHandler(messagesResponseCompleted);
}
void messagesResponseCompleted(object sender, DownloadStringCompletedEventArgs e)
{
lock (this)
{
try
{
string s = e.Result;
if (s.Length > 0)
{
List<Message> messagesResult = JSONHelper.Deserialize<List<Message>>(s);
foreach (Message m in messagesResult)
{
tbMessages.Text += m.message + "\n";
}
}
else
{
tbMessages.Text += "No new messages #: " + System.DateTime.Now + "\n";
}
}
catch (System.Net.WebException we)
{
MessageBox.Show(we.Message);
}
}
}
Anyone?

Answer 1

The WebClient response is processed on the UI thread - so you don't need the lock that you have in your event handler.
For your particular problem - is this just occurring in the emulator? I've seen quite a few timer issues with the emulator - but never anything similar on the real phone.
As an aside, I believe in general it's better to use HttpWebRequest rather than WebClient - see the explanation here of webclient using the UI thread Silverlight Background Thread using WebClient - for your particular code I don't think this will be a problem.

Answer 2

If using
System.Windows.Threading.DispatcherTimer myDispatcherTimer = new System.Windows.Threading.DispatcherTimer();
myDispatcherTimer.Interval = new TimeSpan(0, 0, 0, 0, 5000);
myDispatcherTimer.Tick += new EventHandler(messagePolling);
myDispatcherTimer.Start();
instead of
new System.Threading.Timer(messagePolling, null, 0, 5000); // every 5 seconds
is working fine =)