Textbox not capturing username

Question

Hi,
I want textbox in my page to capture user name after user login.
I tried using the code below,but nothing happens,the textbox is still empty.
Anyone knows what is wrong with this code?
Did i missed something here?

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using System;
using System.Collections;
using System.Configuration;
using System.Data;
using System.Linq;
using System.Web.Caching;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.HtmlControls;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Xml.Linq;
namespace Project
{
    public partial class Master : System.Web.UI.MasterPage
    {
        protected void Page_Load(object sender, EventArgs e)
        {
            if (User.Identity.IsAuthenticated)
            {
                TextBox1.Text = "Welcome " + User.Identity.Name;
            }
            else
            {
                TextBox1.Text = "Welcome user";
            }
        }

    }
}