The control collection cannot be modified because the control contains a code block

Posted by dnamroud on Wed, 19 Feb 2020 11:10:39 +0100

I tried to create a simple user control, which is a slider. When I add the Ajax toolkit sliderextender to the user control, this error appears (* & $() @:

Server Error in '/' Application. The Controls collection cannot be modified because the control contains code blocks (i.e. `<% ... %>`). Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.

Exception Details: System.Web.HttpException: The Controls collection cannot be modified because the control contains code blocks (i.e. `<% ... %>`).

Source Error:

An unhandled exception was generated during the execution of the current web request. Information regarding the origin and location of the exception can be identified using the exception stack trace below.

Stack Trace:

[HttpException (0x80004005): The Controls collection cannot be modified because the control contains code blocks (i.e. `<% ... %>`).]    System.Web.UI.ControlCollection.Add(Control child) +8677431    AjaxControlToolkit.ScriptObjectBuilder.RegisterCssReferences(Control control) in d:\E\AjaxTk-AjaxControlToolkit\Release\AjaxControlToolkit\ExtenderBase\ScriptObjectBuilder.cs:293 AjaxControlToolkit.ExtenderControlBase.OnLoad(EventArgs e) in d:\E\AjaxTk-AjaxControlToolkit\Release\AjaxControlToolkit\ExtenderBase\ExtenderControlBase.cs:306 System.Web.UI.Control.LoadRecursive()
+50    System.Web.UI.Control.LoadRecursive()
+141    System.Web.UI.Control.LoadRecursive()
+141    System.Web.UI.Control.LoadRecursive()
+141    System.Web.UI.Control.LoadRecursive()             
+141    System.Web.UI.Control.LoadRecursive()
+141    System.Web.UI.Control.LoadRecursive()
+141    System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +627


Version Information: Microsoft .NET Framework Version:2.0.50727.3074; ASP.NET Version:2.0.50727.3074

I tried to place a placeholder in the user control and programmatically add a text box and slider extender to the placeholder, but there were still errors.

This is simple code:

<table cellpadding="0" cellspacing="0" style="width:100%">
    <tbody>
        <tr>
            <td></td>
            <td>
                <asp:Label ID="lblMaxValue" runat="server" Text="Maximum" CssClass="float_right" />
                <asp:Label ID="lblMinValue" runat="server" Text="Minimum" />
            </td>
        </tr>
        <tr>
            <td style="width:60%;">
                <asp:CheckBox ID="chkOn" runat="server" />
                <asp:Label ID="lblPrefix" runat="server" />:&nbsp;
                <asp:Label ID="lblSliderValue" runat="server" />&nbsp;
                <asp:Label ID="lblSuffix" runat="server" />
            </td>
            <td style="text-align:right;width:40%;">                

                    <asp:TextBox ID="txtSlider" runat="server" Text="50" style="display:none;" />
                    <ajaxToolkit:SliderExtender ID="seSlider" runat="server" 
                        BehaviorID="seSlider" 
                        TargetControlID="txtSlider" 
                        BoundControlID="lblSliderValue" 
                        Orientation="Horizontal" 
                        EnableHandleAnimation="true" 
                        Length="200" 
                        Minimum="0" 
                        Maximum="100" 
                        Steps="1" />

            </td>
        </tr>
    </tbody>
</table>

What is the problem?

#1 building

First, start the block with <% instead of <% =:

<head id="head1" runat="server">
  <title>My Page</title>
  <link href="css/common.css" rel="stylesheet" type="text/css" />
  <script type="text/javascript" src="<%# ResolveUrl("~/javascript/leesUtils.js") %>"></script>
</head>

This changes the code block from the Response.Write code block to a data binding expression.
The CLR will not complain because the data binding expression is not a code block. Then, in the master page code, add the following:

protected void Page_Load(object sender, EventArgs e)
{
  Page.Header.DataBind();    
}

#2 building

I had the same problem, but it had nothing to do with JavaScript. Consider the following code:

<input id="hdnTest" type="hidden" value='<%= hdnValue %>' />
<asp:PlaceHolder ID="phWrapper" runat="server"></asp:PlaceHolder>
<asp:PlaceHolder ID="phContent" runat="server" Visible="false">
    <b>test content</b>
</asp:PlaceHolder>

In this case, even if PlaceHolders does not have any harmful code blocks, you will encounter the same error, which occurs because the non server control hdnTest uses code blocks.

Just add runat = server to hdnTest to solve the problem.

#3 building

I have the same problem. I found the following solution.

Solution 1: I keep the script tag in my body.

<body>
   <form> . . . .  </form>
    <script type="text/javascript" src="<%= My.Working.Common.Util.GetSiteLocation()%>Scripts/Common.js"></script> </body>

Now, the conflict about tags will be resolved.

Solution 2:

We can also solve one of the above solutions, for example, replace code block with <% = instead of <%, but the problem is that it only gives relative path. If you want a real absolute path, it won't work.

Solution 1 works for me. Next is your choice.

#4 building

The "<%" data binding technology will not be used directly in the < link > tag in the < head > tag:

<head runat="server">

  <link rel="stylesheet" type="text/css" 
        href="css/style.css?v=<%# My.Constants.CSS_VERSION %>" />

</head>

The above code will be evaluated as

<head>

  <link rel="stylesheet" type="text/css" 
        href="css/style.css?v=&lt;%# My.Constants.CSS_VERSION %>" />

</head>

Instead, you should do the following (note the two double quotes):

<head runat="server">

  <link rel="stylesheet" type="text/css" 
        href="css/style.css?v=<%# "" + My.Constants.CSS_VERSION %>" />

</head>

Then you get the ideal result:

<head>

  <link rel="stylesheet" type="text/css" href="css/style.css?v=1.5" />

</head>

#5 building

Keep the Java script code in the body tag

<body> 
   <script type="text/javascript">
   </script>
</body>

Topics: Javascript Java

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