Why is page.Master null/nothing inside of a Shared WebMethod?

Question

The masterpagefile and mastertype is set on the page markup. Why is page.Master equal to null, i.e. nothing inside of a Shared WebMethod?

Here is my code below.

 <WebMethod>_
Public Shared Function CreateNewTab(tabText As String) As String
    Dim page = TryCast(HttpContext.Current.Handler, _Default)
    If page IsNot Nothing Then
        Dim master As SiteMaster = page.Master
        If master IsNot Nothing Then
            Dim cph As ContentPlaceHolder = master.FindControl("MainContent")
            Dim tabContainer As AjaxControlToolkit.TabContainer = cph.FindControl("TabContainer1")
        End If
    End If
    Return tabText
End Function

Answer 1

Because the page, both master and content page, does not actually exist in the ASP.NET AJAX Page Method. There is no instance of the content page, therefore no reference to the master page. That is what Shared (static in C#) means, it is void of an instance of the class, in your case the class is the content page class.

For more information read Why do ASP.NET AJAX page methods have to be static?.

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UPDATE:

There is no way to get access to the server controls, because they are part of the instance of the page, you can however get access to the Session object, by decorating your ASP.NET AJAX Page Method, like this:

Put a value into Session:

<WebMethod(EnableSession := True)> _
Public Shared Sub StoreSessionValue(sessionValue As String)
    HttpContext.Current.Session("TheSessionValue") = sessionValue
End Sub

Retrieve a value from Session:

<WebMethod(EnableSession := True)> _
Public Shared Function GetSessionValue() As String
    Return HttpContext.Current.Session("TheSessionValue").ToString()
End Sub