Get absolute url in a shared function how please?

Hello everyone, I have this shared function and I need to get the absolute url. Here is my code:
<System.Web.Services.WebMethod(True)> _ Public Shared Function RedirectToPage(cevent As CalendarEvent) As String Dim idList As List(Of Integer) = DirectCast(System.Web.HttpContext.Current.Session("idList"), List(Of Integer)) If idList IsNot Nothing AndAlso idList.Contains(cevent.id) Then Dim url As String 'Relative url is "~/testing/default.aspx" 'I want the url to become http://localhost:12234/MySite/testing/default.aspx. when it is hosted, it will be http://www.example.com/testing/default.aspx Return url End If Return "error" End Function Thanks