使用visual basic登录时，StartIndex不能小于零

Question

你好我正在尝试使用visual basic登录Instagram，没有错误，但是当我尝试运行它时，我在这一行得到了一个ArgumentOutOfRangeException：

Dim token As String = html.Substring(html.IndexOf("csrfmiddlewaretoken")).Split(""""c)(2)

这是整个来源：

Imports System.IO
Imports System.Net
Imports System.Text

Public Class Form1
    Dim CC As New CookieContainer
    Dim RQ As HttpWebRequest
    Dim RP As HttpWebResponse
    Public Function GetResponse(ByVal url As String, ByVal referer As String) As String
        RQ = CType(HttpWebRequest.Create(url), HttpWebRequest)
        RQ.CookieContainer = CC

        If referer <> "" Then
            RQ.Referer = referer
        End If

        RP = CType(RQ.GetResponse(), HttpWebResponse)

        Return New StreamReader(RP.GetResponseStream()).ReadToEnd()
    End Function

    Public Function GetResponse(ByVal url As String, ByVal post As String, ByVal referer As String) As String
        RQ = CType(HttpWebRequest.Create(url), HttpWebRequest)
        RQ.Method = "POST"
        RQ.CookieContainer = CC
        RQ.UserAgent = "AppleWebKit/537.36 (KHTML, like Gecko) Mozilla/5.0 (Windows NT 6.1) Chrome/28.0.1468.0 Safari/537.36"

        If referer <> "" Then
            RQ.Referer = referer
        End If

        Dim byteArr() As Byte = Encoding.Default.GetBytes(post)
        RQ.ContentLength = byteArr.Length

        Dim dataStream As Stream = RQ.GetRequestStream()
        dataStream.Write(byteArr, 0, byteArr.Length)

        RP = CType(RQ.GetResponse(), HttpWebResponse)

        Return New StreamReader(RP.GetResponseStream()).ReadToEnd()
    End Function
    Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
        Dim html As String = GetResponse("https://instagram.com/accounts/login/", "")
        Dim token As String = html.Substring(html.IndexOf("csrfmiddlewaretoken")).Split(""""c)(2)
        Dim username As String = TextBox1.Text
        Dim password As String = TextBox2.Text

        Dim S_B As New StringBuilder
        S_B.Append("csrfmiddlewaretoken=" & token)
        S_B.Append("&username=" & username)
        S_B.Append("&password=" & password)

        html = GetResponse("https://instagram.com/accounts/login/", S_B.ToString, "https://instagram.com/accounts/login/")

        If html.Contains("""username"":""" & username) Then
            MsgBox("Successfully Logged In", MessageBoxIcon.Information)
        ElseIf html.Contains("Please enter a correct username and password.") Then
            MsgBox("Invalid Username or Password", MessageBoxIcon.Error)
        Else
            MsgBox("Unable Login Error", MessageBoxIcon.Error)
        End If
    End Sub
End Class

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