public MainViewModel(AppBootstrapper appBootstrapper, IViewStackService viewStackService = null, IFirebaseAuthService firebaseAuthService = null)
{
viewStackService = viewStackService ?? Locator.Current.GetService <IViewStackService>();
firebaseAuthService = firebaseAuthService ?? Locator.Current.GetService <IFirebaseAuthService>();
MenuItems = GetMenuItems();
NavigateToMenuItem = ReactiveCommand.CreateFromObservable <IPageViewModel, Unit>(
pageVm => viewStackService.PushPage(pageVm, resetStack: true));
this.WhenAnyValue(x => x.Selected)
.Where(x => x != null)
.StartWith(MenuItems.First())
.Select(x => Locator.Current.GetService <IPageViewModel>(x.TargetType.FullName))
.InvokeCommand(NavigateToMenuItem);
SignOut = ReactiveCommand.Create(() => firebaseAuthService.SignOut());
SignOut.Subscribe(_ => appBootstrapper.MainView = new SignInViewModel(appBootstrapper));
}