So the solution that I found, thanks to Servy in this post : Using async/await with void method
I managed to use async/await to load the data.
I replaced my LoadData() method by :
public static Task<ObservableCollection<theater>> WhenGetTheaters(ServiceClient client)
{
var tcs = new TaskCompletionSource<ObservableCollection<theater>>();
EventHandler<ServiceReference1.GetTheatersCompletedEventArgs> handler = null;
handler = (obj, args) =>
{
tcs.SetResult(args.Result);
client.GetTheatersCompleted -= handler;
};
client.GetTheatersCompleted += handler;
client.GetTheatersAsync();
return tcs.Task;
}
public async Task LoadData()
{
var theatersTask = WhenGetTheaters(client);
Theaters = await theatersTask;
IsDataLoaded = true;
}
And in my page :
protected override async void OnNavigatedTo(NavigationEventArgs e)
{
if (!App.ViewModel.IsDataLoaded)
{
await App.ViewModel.LoadData();
}