{ return selectedRoom; } private set { this.SetProperty(ref this.selectedRoom, value); } } public string UserName { get { return username; } private set { this.SetProperty(ref this.username, value); } } ReadOnlyReactiveProperty<string> Title = service.ObserveProperty(x => x.SelectedRoom).Select(x => x?.Name) .CombineLatest( service.ObserveProperty(x => x.UserName), (roomname, username) => $"{username} - {roomname}" ) .ToReadOnlyReactiveProperty();