public MainPage()
        {
            this.InitializeComponent();

            DataContext = viewModel = new ContactsViewModel();
            this.Loaded += MainPage_Loaded;
            AuthenticationHelper.PlatformParameters = new PlatformParameters(PromptBehavior.Auto, false);
        }
 public ContactsSource(ContactsViewModel viewModel, ContactsViewController controller)
 {
   this.viewModel = viewModel;
   this.controller = controller;
 }