Question about vba in PPT(Microsoft PowerPoint )

I want display a progress bar when showing ppt. I write code like this:

Public WithEvents App As Application
Private Sub App_SlideShowNextSlide(ByVal Wn As SlideShowWindow)
    Dim Showpos As Integer
    Showpos = Wn.View.CurrentShowPosition
    Dim PageCount As Integer
    PageCount = Application.ActivePresentation.Slides.Count
    SlideShowWindows(Index:=1).View.PointerType = ppSlideShowPointerPen
    Dim i As Integer
    For i = 1 To 15
        Wn.View.DrawLine 0, i, 700 * Showpos / PageCount, i
    Next

End Sub

using abov开发者_运维问答e code, a progress bar appear when I show the PPT. But when I turn to next slide，The progress bar appear and disappear quickly.I wonder why it happens.And how to prevent the progress bar disappearing.Thanks

It's kind of ugly, but you could turn off the screen updating in between slides: http://skp.mvps.org/ppt00033.htm