关于PPT（Microsoft PowerPoint）中vba的问题

我想在显示ppt时显示进度条。 我编写的代码如下：

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

使用上面的代码，当我显示PPT时会出现一个进度条。

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但当我转到下一张幻灯片时，进度条会快速出现和消失。我想知道为什么会出现这种情况。以及如何防止进度条消失。谢谢，这有点难看，但您可以在幻灯片之间关闭屏幕更新：