Overriding the OnBackPressed activity

With our iOS implementation we integrated an override to the navigation back button, so when a user leaves the ClientListViewController, we ask the user if they would like to signout from the ChatHub. We are going to do the same here but on the Android platform. We will be building the alert from the AlertDialog.Builder framework:

public override void OnBackPressed()
         {
             //Put up the Yes/No message box
             AlertDialog.Builder builder = new AlertDialog.Builder(this);
             builder
                 .SetTitle("Chat")
                 .SetMessage("Would you like to signout?")
                 .SetNegativeButton("No", (sender, e) => { })
                 .SetPositiveButton("Yes", (sender, e) =>
                      {
                          _presenter.Signout();
                     })
                 .Show();
         }

We start with instantiating...