(Vb.Net)How Can I Get Frame.Length In Ie_Documentcomplete(Sorry For My Poor English)

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VB

IE

My Question is how can i get frame.length in IE_DocumentComplete.

my code: (vb.net 2013)

Public Class Form1<br />
    Private WithEvents IE As SHDocVw.InternetExplorer<br />
    Private Doc As mshtml.HTMLDocument<br />
<br />
    Private Sub IE_DocumentComplete(pDisp As Object, ByRef URL As Object) Handles IE.DocumentComplete<br />
        Doc = IE.Document<br />
        MsgBox(Doc.frames.length)  ' **System.InvalidCastException error here**<br />
    End Sub<br />
<br />
    Private Sub main_Load(sender As Object, e As EventArgs) Handles MyBase.Load<br />
        IE = New SHDocVw.InternetExplorer()<br />
        IE.Visible = True<br />
<br />
        IE.Navigate("https://www.google.co.jp")<br />
        waitIE(IE)<br />
<br />
   End Sub<br />
<br />
    Private Sub waitIE(ByVal objIE As SHDocVw.InternetExplorer)<br />
        Do Until objIE.ReadyState = SHDocVw.tagREADYSTATE.READYSTATE_COMPLETE Or objIE.Busy = False<br />
            Application.DoEvents()<br />
            'System.Threading.Thread.Sleep(100)<br />
        Loop<br />
<br />
        Do While objIE.Document.ReadyState <> "complete"<br />
            Application.DoEvents()<br />
        Loop<br />
    End Sub<br />
End Class

Thanks for your Help
Greets
Mame