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POListbox not always adding item using Windows Azure MobileServiceCollection with WP8
 

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  1. POListbox not always adding item using Windows Azure MobileServiceCollection with WP8
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    <p>I'm using Windows Azure Mobile Services to store and retrieve data in my Windows Phone 8 app. This is a bit of a complicated issue so I will do my best to explain it.</p> <p>Firstly I'm using raw push notifications to receive a message and when it receives the message it updates a listbox in my app. When I open my app, navigate to the page with the <code>ListBox</code> and receive a push notification the <code>ListBox</code> updates fine. If I press back, then navigate to the same page with the <code>ListBox</code>, the push notification is received, the code to update the <code>ListBox</code> executes with no errors yet the <code>ListBox</code> doesn't update. I have checked that the same code runs using the <code>OnNavigatedTo</code> handler in both scenarios, but it seems like the <code>ListBox</code> does not bind correctly in the second instance when I press back and then re-navigate to the same page. Here are some code snippets:</p> <p>MobileServiceCollection declarations:</p> <pre class="lang-cs prettyprint-override"><code>public class TodoItem { public int Id { get; set; } [JsonProperty(PropertyName = "text")] public string Text { get; set; } } private MobileServiceCollection&lt;ToDoItem, ToDoItem&gt; TodoItems; private IMobileServiceTable&lt;TodoItem&gt; todoTable = App.MobileService.GetTable&lt;TodoItem&gt;(); </code></pre> <p>Push Notification Received Handler:</p> <pre class="lang-cs prettyprint-override"><code>void PushChannel_HttpNotificationReceived(object sender, HttpNotificationEventArgs e) { string message; using (System.IO.StreamReader reader = new System.IO.StreamReader(e.Notification.Body)) { message = reader.ReadToEnd(); } Dispatcher.BeginInvoke(() =&gt; { var todoItem = new TodoItem { Text = message, }; ToDoItems.Add(todoItem); } ); } </code></pre> <p>I have tried using:</p> <pre class="lang-cs prettyprint-override"><code>ListItems.UpdateLayout(); </code></pre> <p>and</p> <pre class="lang-cs prettyprint-override"><code>ListItems.ItemsSource = null; ListItems.ItemsSource = ToDoItems; </code></pre> <p>before and after the code in the above procedure that adds the <code>ToDoItem</code> but it didn't help.</p> <p>The following procedure is called in my <code>OnNavigatedTo</code> event handler, and refreshes the <code>Listbox</code> and assigns <code>ToDoItems</code> as the items source:</p> <pre class="lang-cs prettyprint-override"><code>private async void RefreshTodoItems() { try { ToDoItems = await todoTable .ToCollectionAsync(); } catch (MobileServiceInvalidOperationException e) { MessageBox.Show(e.Message, "Error loading items", MessageBoxButton.OK); } ListItems.ItemsSource = ToDoItems; } </code></pre> <p>The above procedure is <code>async</code> but I have made sure it completes before receiving any notifications. Even so, as mentioned above when I open the app, navigate to the page that shows the <code>ListBox</code> it updates fine. When I press back, navigate to the same page again, it doesn't work. When I back out of the app, re-open it, navigate to the page with the <code>ListBox</code>, it works again, and then fails if I press back and re-open the page. So it seems the <code>ListBox</code> is not binding to <code>ToDoItems</code> correctly when I press back and navigate to the same page.</p> <p>Any help appreciated. Thanks.</p>
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    1. COI think I have found the issue. I have to close the push channel on navigatedfrom and so it opens a new one when I come back to it and it works fine. Closing the push channel isn't in any WP or Azure doco examples I've been looking at so I missed it.
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