Question

I want to create a user control DerivedUserControl.ascx that derives form another user control BaseUserControl.ascx. The base user control derives from System.Web.UI.UserControl as required. These user controls are defined in different folders. Because I’m using a Visual Studio 2010 Web Site project (I’m not able to switch to Web Application project), these user controls are not defined inside a namespace.

My problem is that when I try to compile the project the base class of the derived user control cannot be resolved (obviously because the compiler doesn’t know what .ascx file defines the base class). Is there a way resolve this issue?

I tried everything I could imagine, without success. Any help would be greatly appreciated.

BaseUserControl.ascx

<%@ Control Language="C#" AutoEventWireup="true" CodeFile="BaseUserControl.ascx.cs" Inherits="BaseUserControl" %>

BaseUserControl.ascx.cs

public partial class BaseUserControl : System.Web.UI.UserControl
{
    protected void Page_Load(object sender, EventArgs e)
    {

    }
}

DerivedUserControl.ascx

<%@ Control Language="C#" AutoEventWireup="true" CodeFile="DerivedUserControl.ascx.cs" Inherits="DerivedUserControl"  %>

DerivedUserControl.ascx.cs

public partial class DerivedUserControl : BaseUserControl
{
    protected void Page_Load(object sender, EventArgs e)
    {

    }
}

Error

The type or namespace name 'BaseUserControl' could not be found

Answer 1

When using ASP.NET Web Site (as apposed to a Web Project) you need to add <@Reference> element to your DerivedUserControl.ascx.

From MSDN it…

Indicates that another user control, page source file, or arbitrary
file located at some virtual path should be dynamically compiled and
linked against the current ASP.NET file (Web page, user control, or
master page) in which this directive is declared.

<%@ Reference VirtualPath="~/FolderName1/BaseUserControl.ascx" %>

Once you’ve done that you can reference it like so

public partial class DerivedUserControl : ASP.foldername1.baseusercontrol_ascx

Where FolderName1 is the folder your BaseUserControl is in.