Back button select case statement

I want to create a select case statement for the back button. I guess my main problem is how to dectect which layout is loaded. So something like this.

Select case Backbutton
case Layout("Main") loaded
Activity.removelayout("Main")
Acitivty.Loadlayout("test")
case layout("Two")loaded
Activity.removelayout("Two")
Acitivty.Loadlayout("THree")

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