I am having aspx page connected to Master page. On aspx page I am having asp:HiddenField.

There is Static Web Method on aspx page and I have called it via jQuery json request.

In this Web Method the hidden field is not accessible.

I want to update the value of Hidden field with session value inside Web Method.

Below is my code:

HTML (on aspx page connected with Master)

<asp:HiddenField ID="hdnLoggedinUser" runat="server" />

Web Method:

[WebMethod(true)]
public static string welcomeuser()
{
    Page page = (Page)HttpContext.Current.Handler;
    HiddenField hdnUser = (HiddenField)page.FindControl("hdnLoggedinUser");

    if (HttpContext.Current.Session["UserName"] != null)
    {
        if (hdnUser != null)
        {
            string m, r;
            m = (String)HttpContext.Current.Session["UserID"];
            r = (String)HttpContext.Current.Session["UserName"];
            hdnUser.Value = r;
        }
    }

    var usr = HttpContext.Current.Session["UserName"].ToString();
    return usr;
}

jQuery:

$.ajax({
    type: "POST", //GET or POST or PUT or DELETE verb
    url: "../DemoApp/admManageAccess.aspx/welcomeuser",
    data: {}, //Data sent to server
    contentType: "application/json; charset=utf-8",
    dataType: "json", //Expected data format from server
    async: false,
    beforeSend: function () {

    },
    success: function (data, Type, xhr) {//On Successfull service call
        if (data.d != '') {
            $('#spnUserName').text('Welcome : ' + data.d);
        }
    },
    error: function (XMLHttpRequest, textStatus, errorThrown) {
        alert(errorThrown);
    },
    complete: function () {

    },
    failure: function () { }
});

In web method if (hdnUser != null) this line is getting null. It is not reading Hidden field on the page