Asp.net code behind not able to access controls in ascx - asp.net

Question

I am fairly new to the .NET scene and have run into a small problem with a simple asp.net app and accessing controls defined on in a .ascx file in the code behind.
Here is my Default.ascx file:
<%# Page Title="Home Page" Language="C#" MasterPageFile="~/Site.master" AutoEventWireup="true"
CodeFile="Default.aspx.cs" Inherits="_Default" %>
<asp:Content ID="HeaderContent" runat="server" ContentPlaceHolderID="HeadContent">
</asp:Content>
<asp:Content ID="BodyContent" runat="server" ContentPlaceHolderID="MainContent">
<p>
<asp:Label AssociatedControlID = "userText" AccessKey = "L" runat="server" ID="userLabel">Username</asp:Label>
<asp:TextBox ID = "userText" runat="server" MaxLength="20" ></asp:TextBox>
</p>
</asp:Content>
Here is the Default.aspx.cs file:
using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
public partial class _Default : System.Web.UI.Page
{
protected void Page_Load(object sender, EventArgs e)
{
}
protected void Page_PreInit(object sender, EventArgs e)
{
userLabel.Text = "Hello!";
}
}
As you can see, pretty straight forward, all I am trying to do is change the text property of a label programmatically. However when I run this I am getting a NullReferenceException, userLabel is not set to an instance of an object. Shouldn't userLabel be a property of my _Default class? I tried explicitly setting userLabel as a property but I get an compile time error saying that userLabel already has a definition.
I imagine I am missing something very simple here but I'm not sure what it is. Could anyone tell me what I am doing wrong? Thanks much!

Answer 1

Page_PreInit is called before controls are rendered. Try adding your code to the Page_Load method.
See Life-Cycle Events section in http://msdn.microsoft.com/en-us/library/ms178472.aspx

Answer 2

Controls are not available until they are initialized; the control has not yet been created at the PreInit event which is why you cannot access it.
Setting values like you are doing should generally be performed at the Load event, or at least after the page Init event has fired.

Answer 3

As you can read here, in the page_perinit you cannot access control because they does not yes exist.
Is a good practice apply theme and personalization during this event, not access the state of the controls

Answer 4

Initialization of controls should be done on Page_Init.
protected void Page_Init(object sender, EventArgs e)
{
userLabel.Text = "Hello!";
}

Answer 5

First of all, you can't simply access label in user control with userLabel.Text. You need to get with Label lbl = (Label)UserControlID.FindControl("userLabel"); in your parent page. (But what you need is to set vale of Label in UserControl from Parent page.)
So I would do as:
Put property in UserControl:
public string UserName {get; set;}
protected void Page_Load(object sender, EventArgs e)
{
userLabel.Text = this.UserName;
}
In page load event of Parent Page, set property value:
protected void Page_Load(object sender, EventArgs e)
{
UserControlID.UserName = "Hello!";
}
Page_Load of parent page will call before usercontrol's page load and it should be ok.

Answer 6

I don't see any label named userLabel. The name of your label seem to bel userText.