public UsersViewModel() { Title = "View Users"; Users = new ObservableCollection <User> (); LoadUsersCommand = new Command(async() => ExecuteLoadUsersCommand()); MessagingCenter.Subscribe <AddUserPage, User>(this, "AddUser", (Action <AddUserPage, User>)(async(obj, user) => { var newUser = user as User; Users.Add((User)newUser); await UserDataStore.AddUserAsync((User)newUser); })); }