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The Controls collection cannot be modified because the control contains code blocks (i.e. <% ... %>).

Posted on 2009-05-18
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Last Modified: 2012-05-07
I am trying to add a meta tag programatically. However, I get the error :

The Controls collection cannot be modified because the control contains code blocks (i.e. <% ... %>)., when trying to add. See code below.

I do not want to move the script in <%...%> in the body as it is present in all my aspx files. How can I get this to work without making any changes in the aspx page.
<%@ Page language="c#" Inherits="Adomo.Web.Login" CodeFile="Default.aspx.cs" Title="<%$ Resources:PageTitle %>" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
 
<html xmlns="http://www.w3.org/1999/xhtml">
	<head runat="server">
		<title />
		<meta name="vs_snapToGrid" content="False" />
		<meta content="Microsoft Visual Studio .NET 7.1" name="GENERATOR" />
		<meta content="C#" name="CODE_LANGUAGE" />
		<meta content="JavaScript" name="vs_defaultClientScript" />
		<meta content="http://schemas.microsoft.com/intellisense/ie5" name="vs_targetSchema" />
		<link href="AdomoCss.css" type="text/css" rel="Stylesheet" /><%
    /*	Add reference for language dependent stylesheet to override layout where needed for non en-US pages. Typically, column widths will be overruled where needed.
Not added for pages called with en-US or with no culture tag (admin pages). */
    if (cultureTag != null && cultureTag != "en-us")
    {
        Response.Write("<link href='AdomoCss." + cultureTag + ".css' type='text/css' rel='Stylesheet' />");
    }
		%>
</head>
 
Adding the html meta tag in code behind in OnLoad method
 
HtmlMeta meta = new HtmlMeta();
meta.HttpEquiv = "X-UA-Compatible";
meta.Content = "IE=EmulateIE7";
this.Header.Controls.Add(meta);

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Question by:anshugupta_fremont
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Assisted Solution

by:tetorvik
tetorvik earned 125 total points
ID: 24418896
There are couple of options I am aware of:

1# remove the Response.Write() and add the css link dynamically in code-behind
http://www.aspdotnetfaq.com/Faq/How-to-Programmatically-add-CSS-Stylesheet-file-to-Asp-Net-page.aspx

2# change the <%= %> to binding expression <%# %>
http://leedumond.com/blog/the-controls-collection-cannot-be-modified-because-the-control-contains-code-blocks/
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Author Comment

by:anshugupta_fremont
ID: 24424028
Do I have any other option (within code behind), that doesnt require change in the aspx file (because , I will have to make this change in 10 other aspx file).

Also, can you please explain why this is happening?

Thanks in Advance
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Accepted Solution

by:
tetorvik earned 125 total points
ID: 24425213
Apparently you are modifying HtmlHead's control collection at code-behind and at aspx page, which is not allowed. I am not aware of the exact reason why this is not allowed.

However I came across one additional hack that gets you around the issue without modifying code-behind code. You'll need to wrap your head (<%=...%>) fragmant with some placeholder (asp:PlaceHolder will do), then you're not modifying the same control collection anymore.
<asp:PlaceHolder runat="server" ID="fbar"> 
<%
  if (cultureTag != null && cultureTag != "en-us")
  {
        Response.Write("<link href='AdomoCss." + cultureTag + ".css' type='text/css' rel='Stylesheet' />");
  }
    
%>
</asp:PlaceHolder>

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