public LoginViewModel() { _userCredentials = new UserCredentials(); this.LoginCommand = new Command(async() => { AppData.Credentials = _userCredentials; var authenticated = await SitecoreHelper.Authenticate(); if (authenticated) { App.Current.MainPage = new NavigationPage( ViewFactory.CreatePageFromViewModel(new WorkboxViewModel())); } ; }, () => !string.IsNullOrEmpty(_userCredentials.InstanceUrl) && !string.IsNullOrEmpty(_userCredentials.Username) && !string.IsNullOrEmpty(_userCredentials.Password)); }