How to register custom server control on ASP.NET page

Question

I have a project and I am trying to register a custom server control (there is no .ascx file) on the page. I am currently using

Class Declaration

namespace MyApp.Controls{
    public class CustomControl: WebControl{
        public string Text
        {
            get
            {
                String s = (String)ViewState["Text"];
                return ((s == null) ? String.Empty : s);
            }
            set
            {
                ViewState["Text"] = value;
            }
        }        
        protected override void RenderContents(HtmlTextWriter output)
        {
            output.Write(Text);
        }
    }
}

On my page,

<%@ Register TagPrefix="myControls" Namespace="MyApp.Controls" %>
<myControls:CustomControl runat="server" Text="What up!" />

I receive a Parser Error, with the message "Unknown server tag 'myControls:CustomControl'."

What am I doing wrong?

Answer 1

Well, if this control is in another class library, or even if it's in the same one, it wouldn't be a bad idea to specify control's assembly in @Register:

<%@ Register TagPrefix="myControls" Namespace="MyApp.Controls" Assembly="MyApp" %>
<myControls:CustomControl runat="server" Text="What's up!" />

Clean and rebuild your solution too in order to verify everything is compiled rightly!

Answer 2

If your control will be reused on several pages, you may want to register it in web.config, as one of system.web/pages/controls subelements instead of copy-pasting the same <@Register tag in all affected pages.

web.config:

<system.web>
  <pages ...>
    <controls>
      ...
      <add tagPrefix="myCompany" namespace="MyCompany.Whatever.Controls" assembly="Whatever"/>
    </controls>

thepage.aspx:

<myCompany:ControlClassName ID="TheStuff" runat="server" ... />

Answer 3

You should put your control either under the App_Code folder (in the case if the control not in assembly) or add a reference to assembly where this control is:

<%@ Register TagPrefix="myControls" Namespace="MyApp.Controls"
      Assembly="SomeAssembly" %>

But guessing, your control not under the App_Code folder.

Answer 4

Add an assembly attribute to your register tag