public UpdateContactPageViewModel(MyContact contactToUpdate, INavigation navigator)
{
this.contactToUpdate = contactToUpdate;
this.navigator = navigator;
dataService = DependencyService.Get <IDataService>();
UpdateCommand = Name.Select(a => !string.IsNullOrEmpty(a)).
CombineLatest(Mobile.Select(b => !string.IsNullOrEmpty(b)),
(a, b) => a && b).ToReactiveCommand();
UpdateCommand.Subscribe(async() => await ExecuteUpdateCommand());
DeleteCommand.Subscribe(async() => await ExecuteDeleteCommand());
MarkFavoriteCommand.Subscribe(async() => ExecuteMarkFavoriteCommand());
UpdatePhotoCommand.Subscribe(async() => await ExecuteUpdatePhotoCommand());
}
