Android Question Back button select case statement

Sub Activity_KeyPress (KeyCode As Int) As Boolean
   If KeyCode = KeyCodes.KEYCODE_BACK Then
      Select layout
         Case  "NewGame" ,"Options", "LoadGame"
            allinvisible
            MainMenu                     
            Return True                                
         Case "HowtoPlay"
            allinvisible
            Options                     
            Return True                 
         Case  "GamePlay"      
            Dim result As Int
            result =    Msgbox2("Exit Game?", "Exit", "Exit", "Main Menu", "Continue playing",Null)
            If result = DialogResponse.POSITIVE Then
               Msgbox(gmid,"gameid")             
               ExitApplication                       
            Else IF result = DialogResponse.CANCEL Then
               allinvisible
               MainMenu                     
               Return True                             
            Else If result = DialogResponse.NEGATIVE Then
               'continue playing             
               Return True
            End If         
         Case "MainMenu"
            ExitApplication                 
      End Select
   End If
End Sub