iOS Question Redisplay the back button after adding a TopLeftButton

Sub Process_Globals
   'These global variables will be declared once when the application starts.
   'Public variables can be accessed from all modules.
   Public App As Application
   Public NavControl As NavigationController
   Private Page1 As Page
   Private page2 As Page
End Sub

Private Sub Application_Start (Nav As NavigationController)
   NavControl = Nav
   Page1.Initialize("Page1")
   Page1.Title = "Page 1"
   Page1.RootPanel.Color = Colors.White
   NavControl.ShowPage(Page1)
   page2.Initialize("page2")
   page2.RootPanel.Color = Colors.Red
   Dim b1 As BarButton
   b1.InitializeText("abc", "abc")
   page2.TopLeftButtons = Array(b1)
End Sub


Sub Page1_Click
   NavControl.ShowPage(page2)
End Sub

Sub page2_BarButtonClick (Tag As String)
   If Tag = "abc" Then
     page2.TopLeftButtons = Array() '<----------------------
   End If
End Sub