Using ASPX Web User Control with Visual Studio 2010 - asp.net

Question

I am trying to implement a Web User Control into one of my APSX pages but keep getting the following warning:
Element 'IntFilter' is not a known element. This can occur if there is a compilation error in the Web site, or the web.config file is missing.
The user control is defined in the same web project as the aspx page.
Question:
How do I resolve this warning (I do not want to move the control to a separate project)?
Also, what do I need to do to enable IntelliSense for this control so I can set its FilterTypeSelection property from ASPX?
Code for "~/FilterControls/IntFilter.ascx"
<%# Control Language="vb" AutoEventWireup="false" CodeBehind="IntFilter.ascx.vb" Inherits="StaffSupport.Filters.IntegerFilter" %>
<asp:DropDownList ID="typeFilterDropDownList" runat="server">
<asp:ListItem Selected="True" Text ="Any" Value="-1" />
<asp:ListItem Selected="False" Text ="Equal" Value= "0" />
</asp:DropDownList><br />
<asp:TextBox ID="TextBox1" runat="server" /><asp:CheckBox ID="CheckBox1" runat="server" Text="Inclusive" /><br />
<asp:TextBox ID="TextBox2" runat="server" /><asp:CheckBox ID="CheckBox2" runat="server" Text="Inclusive" /><br />
Code for "~/FilterControls/IntFilter.ascx.vb"
Namespace Filters
Public Class IntegerFilter
Inherits System.Web.UI.UserControl
Public Enum NumberFilterTypes As SByte
Any = -1
Equals = 0
End Enum
Public Property FilterTypeSelection As NumberFilterTypes
Get
Dim value As SByte
If Not Integer.TryParse(typeFilterDropDownList.SelectedValue, value) Then
value = -1
End If
Return CType(value, NumberFilterTypes)
End Get
Set(value As NumberFilterTypes)
typeFilterDropDownList.SelectedValue = CSByte(value)
End Set
End Property
Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
End Sub
End Class
End Namespace
Code for "OpenCases.aspx"
<%# Page Title="" Language="vb" AutoEventWireup="false" MasterPageFile="~/StaffSite.Master" CodeBehind="OpenCases.aspx.vb" Inherits="StaffSupport.OpenCases" %>
<%# Register TagPrefix="filters" TagName="IntFilter" src="~/FilterControls/IntFilter.ascx" %>
<asp:Content ID="bodyContent" ContentPlaceHolderID="cphBody" runat="server">
ID<br />
<filters:IntFilter ID="IntFilter1" runat="server" />
</asp:Content>
Code for "OpenCases.aspx.vb"
Public Class OpenCases
Inherits System.Web.UI.Page
Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
Page.ViewStateMode = UI.ViewStateMode.Disabled
End Sub
Update 2012/02/21:
Fixed the "filters" vs "filter" miss match.
Also of note, if you drag the control from the Solution Explorer to the page in Design view it will add the references you need (though it was still generating the warning for me). If you drag it to the page in source view it will add an a tag with a href to the element.
Update 2012/02/21 b:
Found the solution, see my answer below.

Answer 1

Apparently you have to reference both the ASCX page and the assembly.
If you drag the ASCX page from the "Solution Explorer" window to the Design view for the page you are editing it will add the reference for the ASCX page, but you will have to add the assembly reference manually.
OpenCases.aspx
<%# Page Title="" Language="vb" AutoEventWireup="false" MasterPageFile="~/StaffSite.Master" CodeBehind="OpenCases.aspx.vb" Inherits="StaffSupport.OpenCases" %>
<%# Register Assembly="StaffSupport" Namespace="StaffSupport.Filters" TagPrefix="filters" %><%-- Assembly Reference --%>
<%# Register TagPrefix="filters" TagName="IntFilter" src="~/FilterControls/IntFilter.ascx" %>
<asp:Content ID="bodyContent" ContentPlaceHolderID="cphBody" runat="server">
ID<br />
<filters:IntFilter ID="IntFilter1" runat="server" />
</asp:Content>
Note: beware of object type collisions. For example the following would also work:
<%# Page Title="" Language="vb" AutoEventWireup="false" MasterPageFile="~/StaffSite.Master" CodeBehind="OpenCases.aspx.vb" Inherits="StaffSupport.OpenCases" %>
<%# Register Assembly="StaffSupport" Namespace="StaffSupport.Filters" TagPrefix="pre1" %><%-- Assembly Reference --%>
<%# Register TagPrefix="pre2" TagName="IntFilter" src="~/FilterControls/IntFilter.ascx" %>
<asp:Content ID="bodyContent" ContentPlaceHolderID="cphBody" runat="server">
ID<br />
<pre1:IntFilter ID="IntFilter1" runat="server" />
</asp:Content>
This is why it started working for me Friday after I posted this, I had added a custom control which implemented System.Web.UI.WebControls.TextBox so I could drag and drop it from the Toolbox. Since it was in the same namespace the control added the assembly reference when it added the control to the page.
Note: if you are referencing dll files which are contained in your project then you may need to remove the page registrations, build, then add the page registrations back. Otherwise the compiler may complain that the dll files are not in the bin.
Update: 2013/04/18
It appears you only need to add the assembly reference if the UserControl is not defined in the same namespace.
If the parrent is defined in Proj.Presentation and the UserControl is defined in Proj.Presentation then you should not need the assembly reference.
If the parrent is defined in Proj.Page and the UserControl is defined in Proj.Page.UserControl then you should not need the assembly reference.
If the parrent is defined in Proj.Page and the UserControl is defined in Proj.UserControl then you need the assembly reference.

Answer 2

The control is declared as:
<%# Register TagPrefix="filters"
and in the markup
<filter:IntFilter
These must match.

Answer 3

You are registering a different prefix from the one you're attempting to use.
You can either change this:
<filter:IntFilter ID="IntFilter1" runat="server" />
to this:
<filters:IntFilter ID="IntFilter1" runat="server" />
Or change this:
<%# Register TagPrefix="filters" TagName="IntFilter"
to this:
<%# Register TagPrefix="filter" TagName="IntFilter"

Answer 4

Close Visual Studio, delete the schema cache, and re-open Visual Studio. You can find the schemas under something like:
C:\Users\Pavel\AppData\Roaming\Microsoft\VisualStudio\10.0\ReflectedSchemas
It is safe to delete all files in this folder.
Delete the contents of that above folder, and all is well.