public MainViewModel(IUserService userService, IUserMessageService userMessageService, FriendsViewModel friendsViewModel) { Title = "Relay Commands Demo"; userService.UserChanged += (s, e) => { CurrentUser = e.NewUser; }; friendsViewModel.Commands.Add(new FriendCommand { Header = "Login with this user", Command = new RelayCommand <UserData>(user => { userService.SetUser(user); }) }); GCCommand = new RelayCommand(() => { GC.Collect(); userMessageService.DisplayMessage("Operation Complete", "Ran GC successfully"); }); }