How Clear Back Stack on Xamarin IOS?

Question

When a user authenticates correctly, it will be directed to the HomeViewModel. I want to remove the possibility that it can return to the login screen so I have created a Custom Presenter to remove all the screens that are below the new screen.

The implementation is as follows:

 public class CustomPresenter: MvxFormsIosPagePresenter
    {
        public CustomPresenter(UIWindow window, MvxFormsApplication mvxFormsApp)
         : base(window, mvxFormsApp)
        {
        }

        public override void Show(MvxViewModelRequest request)
        {

            if (request.PresentationValues?["NavigationCommand"] == "StackClear")
            {
                var navigation = FormsApplication.MainPage.Navigation;
                Debug.WriteLine("Navigation Back Stack Count -> " + navigation.NavigationStack.Count());
                navigation.PopToRootAsync();
                Debug.WriteLine("Navigation Back Stack Count After PopToRootAsync -> " + navigation.NavigationStack.Count());
                return;
            }

            base.Show(request);
        }
    }

When the authentication process finishes correctly, I navigate to the home screen by passing a bundle with this special command:

LoginWithFacebookCommand.Subscribe(token => {
                Debug.WriteLine("JWT Token -> " + token);
                _userDialogs.ShowSuccess(AppResources.Login_Success);
                var mvxBundle = new MvxBundle(new Dictionary<string, string> { { "NavigationCommand", "StackClear" } });
                ShowViewModel<HomeViewModel>(presentationBundle: mvxBundle);
            });

The problem is that it does not change the screen, it stays in the current one. What would be the way to do it correctly ?.

I am using MvvmCross 5.1.1 and MvvmCross.Forms 5.1.1

Thank you very much in advance.

Answer 1

As I understand it, PopToRootAsync() pops everything off the stack to the root. Which means you should then push your view that you wish to navigate to, onto your stack after that method is called i.e. use PushViewController(yourViewController) afterwards. Also, you should be using the new IMvxNavigationService by MvvmCross. You can give this a try:

var navigationService = Mvx.Resolve<IMvxNavigationService>();

LoginWithFacebookCommand.Subscribe(async (token) => {
                Debug.WriteLine("JWT Token -> " + token);

                _userDialogs.ShowSuccess(AppResources.Login_Success);

                await navigationService.Navigate<HomeViewModel>();
            });

To clear the backstack you basically need to override the Show method in the presenter and check whether your viewmodel is being called. If it is then set a new array of viewControllers. (Credit to @pnavk!!)

public class CustomPresenter : MvxIosViewPresenter
    {
        public override void Show(IMvxIosView view, MvxViewModelRequest request)
        {
            if (MasterNavigationController != null && view.ViewModel.GetType() == typeof(HomeViewModel))
            {
                var viewController = view as UIViewController;
                MasterNavigationController.SetViewControllers(new UIViewController[] { viewController }, true);
            }
            else
                base.Show(view, request);
        }
    }

Answer 2

Try this:

navigation.SetViewControllers(new UIViewController[] { vc }, true);

vc is the ViewController you want to set as the root of the navigation stack. You will need to get a reference to it which you can using the ViewControllers property on the NavigationController.

true - means you want to animate.