Get Paypal Express cart Price right before checkout

I am using paypal express checkout and I'm trying to get the total value that is in the shopping cart when the user decides to checkout. My shipping rate is going to be based on the total price and although I have the shipping calculations filled out in my paypal account settings, the shipping cost is not showing up in the checkout screen. How would I grab the total shopping cart price right upon checkout so that I can add the shipping cost? What I have so far is only the values after the user has checked out and they are returned back to my website but at this point it is too late to add shipping.

Dim authToken As String = "sdf5414FdsfDFS5eEF52s336DFLLJUhhbuzek64"
    Dim txToken As String = Request.QueryString("tx")
    txToken = "4GGSES84eEWSS" 
    Dim strRequest As String = "cmd=_notify-synch&tx=" & txToken & "&at=" & authToken

    'Dim Payerinfo As New PayerInfo
    'Dim trans As New Transaction
    'Dim tra As New PayPal.PayPalAPIInterfaceService.Model.GetTransactionDetailsReq




    'post back to either sandbox or live
    Dim strSandbox As String = "https://www.sandbox.paypal.com/cgi-bin/webscr"
    Dim strLive As String = "https://www.paypal.com/cgi-bin/webscr"
    Dim req As HttpWebRequest = CType(WebRequest.Create(strSandbox), HttpWebRequest)
    'req.Headers = valHeader
    'Set values for the request back
    req.Method = "POST"
    req.ContentType = "application/x-www-form-urlencoded"
    req.ContentLength = strRequest.Length

    'Send the request to PayPal and get the response
    Dim streamOut As StreamWriter = New StreamWriter(req.GetRequestStream(), Encoding.ASCII)
    streamOut.Write(strRequest)
    streamOut.Close()
    Dim streamIn As StreamReader = New StreamReader(req.GetResponse().GetResponseStream())
    Dim strResponse As String = streamIn.ReadToEnd()
    streamIn.Close()

    If Not String.IsNullOrEmpty(strResponse) Then

        Dim results As New Dictionary(Of String, String)
        Dim reader As New StringReader(strResponse)
        Dim line As String = reader.ReadLine()
        If line = "SUCCESS" Then
            'FormView1.Visible = False
            While True
                Dim aLine As String
                aLine = reader.ReadLine
                If aLine IsNot Nothing Then
                    Dim strArr() As String
                    strArr = aLine.Split("=")
                    results.Add(strArr(0), strArr(1))
                Else
                    Exit While
                End If
            End While

            ' Displays all the keys for results, helps to see what the keys are named for writing to text file

            For Each kvp As KeyValuePair(Of String, String) In results
                Dim v1 As String = kvp.Key
                Dim v2 As String = kvp.Value
                Response.Write(v1.ToString _
                        + ":  " + v2 + "<br /> ")
            Next

        End If

I have also been trying to declare a session variable and add to it every time the add to cart button is clicked but I see a problem in this because I don't know how long the items will stay in the paypal cart and if the session variable session runs out of time and is cleared, they will then receive free shipping since the shipping amount clears out. Is their any way to make this work?

Protected Sub AddToCartBtn_Click(sender As Object, e As EventArgs)
Session("CartAmount")     

 Dim itemNumber As String = str2
    Dim itemAmount As String = price
    Dim currencyCode As String = "USD"
    Dim addItem As Integer = 1

    Dim ppHref As StringBuilder = New StringBuilder()
    ppHref.Append("https://www.sandbox.paypal.com/cgi-bin/webscr?cmd=_cart")
    ppHref.Append("&business=" + business)
    ppHref.Append("&item_name=" + itemName)
    ppHref.Append("&item_number=" + itemNumber)
    ppHref.Append("&amount=" + itemAmount)
    ppHref.Append("&currency_code=" + currencyCode)   
Session("CartAmount") = (cartTotal + Session("CartAmount"))
End Sub

---

您可以通过以下url参考提供的变量传递购物车值，https://developer.paypal.com/docs/classic/paypal-payments-standard/integration-guide/Appx_websitestandard_htmlvariables/#id08A6HF080O3

链接地址: http://www.djcxy.com/p/35912.html

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