Send user to login page if logged out

I am using Parse in my app to handle my users.
If the user chooses to log out how do I send them to my LoginView.

LoginView -> pushModel -> TabPage -> DashboardView (Press logout) -> Go back to LoginView

In my App.cs I am checking if the user is already logged in or not and either push them to the login or right to there dashboards.
I am going to check if the user is logged in, in every ViewModel with OnViewAppearing (XLabs) is there a better way to do this? Like making a central place control this by listening to an event?