asp.net user control element is null

Question

I have a simple asp.net user control:

<%@ Control Language="C#" AutoEventWireup="true" 
    CodeBehind="QueryDefinitionItem.ascx.cs"
    Inherits="xxx.UserControls.QueryDefinitionItem" %>
    <link href="../Styles/Site.css" rel="stylesheet" type="text/css" />
    <div class="title">
      <h1 id="TextField" runat="server"></h1>
    </div>

Code behind:

 public partial class QueryDefinitionItem : System.Web.UI.UserControl
{
    private string m_text;
    protected void Page_Load(object sender, EventArgs e)
    {
        TextField.InnerText = m_text;
    }

    public void SetText(string text)
    {
        m_text = text;
    }
}

I use LoadControl to load one instance programatically:

protected void Page_Load(object sender, EventArgs e)
    {
        var control = (QueryDefinitionItem)LoadControl(typeof (QueryDefinitionItem),null);
        control.SetText("test2");
        itemsPanel.Controls.Add(control);}

I then use the SetText function to set the text and once the Page Load is fired I get a NullReferenceException that says TextField is null...

I cant figure out why.

At what point are you adding the control dynamically ?

Richard Friend
– Richard Friend

2012-01-03 09:34:28 +00:00
Commented Jan 3, 2012 at 9:34 — Richard Friend
– Richard Friend, Commented Jan 3, 2012 at 9:34
@RichardFriend Its the page load event of the page

Amit Raz
– Amit Raz

2012-01-03 09:41:08 +00:00
Commented Jan 3, 2012 at 9:41 — Amit Raz
– Amit Raz, Commented Jan 3, 2012 at 9:41

KV Prajapati · Accepted Answer · 2012-01-03 10:20:17Z

3

You should have to use LoadControl(string) method instead of LoadControl(Type,Param) and store value directly to the HtmlControl. (There is bug take a look at connect).

protected void Page_Load(object sender, EventArgs e)
{
}
public void SetText(string text)
{
  TextField.InnerText = text;
}

Or create a property,

   public string Text
    {
      get { return TextField.InnerText; }
      set { TextField.InnerText=value;  }
    }

Use Page_Init or Page_Load event to create controls dynamically.

protected void Page_Load(object sender, EventArgs e)
  {
  var control = (QueryDefinitionItem)LoadControl("~/QueryDefinitionItem.ascx");
  control.SetText("test2");
  itemsPanel.Controls.Add(control);
  }

edited Jan 3, 2012 at 10:20

answered Jan 3, 2012 at 9:30

KV Prajapati

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2 Comments

Pawan Nogariya Over a year ago

@Amit Where are you trying to access that TextField. I mean in which event it is returning you null. Is it Page_Load of control or the page where you are creating it?

Amit Raz Over a year ago

@AVD I am creating the user control at the page load event of the page and I have tried to access it on the page load of the control. I have also tried accesing it (user the method you offered) directly from the page load of the page.

hackp0int · Accepted Answer · 2012-01-03 09:46:48Z

0

Try to use the same code but in page pre render should work.

answered Jan 3, 2012 at 9:46

hackp0int

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Comments

Richard Friend · Accepted Answer · 2012-01-03 10:23:46Z

0

Swap these around

control.SetText("test2");   
itemsPanel.Controls.Add(control);

Becomes

itemsPanel.Controls.Add(control);
control.SetText("test2");

Your user control will not have created its control tree until it is added to the control tree itself.

You can also use EnsureChildControls to make sure it has created its controls.

public void SetText(string text)  { 
    EnsureChildControls();
    TextField.InnerText = text;  
}

I would also recommend creating your control before page_load, this is a good read

answered Jan 3, 2012 at 10:23

Richard Friend

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