How to wait for an async call to complete on WP7? - windows-phone-7

Question

I'm loading pivot items based on a call a webservice call. Given that all I have is asynchronous calls available, how do I go about catching when it's finished?
My main reason is that I'd like to keep a loading dialog up while it's waiting for the callback. However, I'm loading in a viewmodel class, and obviously the loading bar is in the page class.
Honestly, if I could just know when one pivot item was loaded, that would be fine, however setting an event handler on loadedpivotitem never seems to trigger.

Answer 1

I assume you are databinding your View to your ViewModel. In that case all you need to do is create a bool property and set it to true while loading/awaiting the async call. You could do something like this:
private bool isSyncing;
public bool IsSynchronizing
{
get { return this.isSyncing; }
set
{
this.isSyncing = value;
this.RaisePropertyChanged(() => this.IsSynchronizing); //Use appropriate RaisePropertyChanged method for your MVVM implementation
}
}
Before starting the async call you would set IsSynchronizing = true. At the end of the eventhandler set IsSynchronizing = false;
From your view you can bind to this bool. For the loadingbar it could be like this:
<ProgressBar Visibility="{Binding IsSynchronizing, Converter={StaticResource booleanToVisibilityConverter}}" IsIndeterminate="{Binding IsSynchronizing}" Style="{StaticResource PerformanceProgressBar}" />
In your scenario you can use an inverted BooleanToVisibilityConverter to hide the pivot while it is still loading.
Hope this helps, let me know if you need more info on using the BooleanToVisibilityConverters

Answer 2

You would need to hook up an event handler similar to as shown in this block of code:
public void LoadData()
{
SampleDataServiceClient client = new SampleDataServiceClient();
client.GetDataCompleted += new EventHandler<GetDataCompletedEventArgs>(client_GetDataCompleted);
client.GetDataAsync();
}
void client_GetDataCompleted(object sender, GetDataCompletedEventArgs e)
{
this.DataContext = e.Result;
}