C# Delegate, Label text not changing

Question

I have created this delegate so that each time I click the button the text within the label's text should change but for some reason this does not work and the label's text does not change.

This is my aspx page:

<body>
    <form id="form1" runat="server">
    <div>
        <asp:Button ID="btnFeed" OnClick="btnFeed_Click" runat="server" Text="Button" />
        <asp:Label ID="lblRaceResults" runat="server" Text="Label"></asp:Label>
    </div>
    </form>
</body>

This is my aspx.cs page

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;

namespace WebProgramming3.Week_3
{
    public partial class Exercise1 : System.Web.UI.Page
    {
        //only for testing
        static Person test_person;
        static Person person2;
        static Person person3;

        protected void Page_Load(object sender, EventArgs e)
        {
            if (!IsPostBack)
            {
                test_person = new Person("Neil");
                person2 = new Person("2");
                person3 = new Person("3");
                test_person.OnFullyFed += Test_person_OnFullyFed;
                person2.OnFullyFed += Test_person_OnFullyFed;
                person3.OnFullyFed += Test_person_OnFullyFed;
            }
        }

        private void Test_person_OnFullyFed(string message)
        {
            // HttpContext.Current.Response.Write(message + " is full");
            lblRaceResults.Text = message; //<--This is the label where text will not change
        }

        protected void btnFeed_Click(object sender, EventArgs e)
        {
            test_person.Feed(1);
            person2.Feed(2);
            person3.Feed(3);
        }
    }

    public delegate void StringDelegate(string message);

    public class Person
    {
        public string Name { get; set; }
        public int Hunger { get; set; }

        public event StringDelegate OnFullyFed;

        public Person(string name)
        {
            Name = name;
            Hunger = 3;
        }

        public void Feed(int amount)
        {
            if(Hunger > 0)
            {
                Hunger -= amount;
                if(Hunger <= 0)
                {
                    Hunger = 0;

                    //this person is full, raise an event
                    if (OnFullyFed != null)
                        OnFullyFed(Name);
                }
            }
        }

    }
}

I am fairly sure that my delegate is coded correctly as when I uncomment the line

HttpContext.Current.Response.Write(message + " is full");

I get a message back each time I click the button

You can read [here](http://stackoverflow.com/questions/3464898/difference-between-page-load-and-onload]). The Page_load is an event handler, it get executed after the load event fired up. but at this stage, all the controls been loaded and sent already. so you label will not changed. Instead of Page_load, you can put them in OnLoad, and remove !IsPostPack, then it will work. — Jonathon, Jan 05 '16 at 21:53

Moe · Accepted Answer · 2016-01-05T21:42:36.357

This is because the page life-cycle has finished and the page rendered / sent to the browser before the threads have finished updating their controls. During debug you can see the threads completing their work but are altering labels that have already been sent to the browser.

Removing the !IsPostBack from you load event should do the trick and reload the controls. Of Course there are other options you could use to resolve this, like having an update panel and auto refresh.

 protected void Page_Load(object sender, EventArgs e)
        {
                test_person = new Person("Neil");
                person2 = new Person("2");
                person3 = new Person("3");
                test_person.OnFullyFed += Test_person_OnFullyFed;
                person2.OnFullyFed += Test_person_OnFullyFed;
                person3.OnFullyFed += Test_person_OnFullyFed;

        }

C# Delegate, Label text not changing

1 Answers1