IsPostBack Property In ASP.NET Web Forms | ASP.NET Web Forms Tutorials | ASP.NET

 using System;

using System.Collections.Generic;

using System.Linq;

using System.Web;

using System.Web.UI;

using System.Web.UI.WebControls;

namespace is_post_back

{

    public partial class WebForm1 : System.Web.UI.Page

    {

        protected void Page_Load(object sender, EventArgs e)

        {

            //When page load first time at that time only "IsPostBack" value will be false

            //When page will load second time or after that any time at that time only "IsPostBack" value will be true

            //if (IsPostBack)

            //{

            //    Response.Write("THIS IS POST BACK REQUEST !!");

            //}

            //if (!IsPostBack)

            //{

            //    Response.Write("THIS IS NOT POST BACK REQUEST !!");

            //}

            if (!IsPostBack)

            {

                AddListBoxItems();

            }

        }

        void AddListBoxItems()

        {

            ListBox1.Items.Add("Item 1");

            ListBox1.Items.Add("Item 2");

            ListBox1.Items.Add("Item 3");

        }

    }

}

Above File is is_post_back\WebForm1.aspx.cs