Declaring a Simple Custom Control

This example demonstrates how easy it is to create custom controls in ASP.NET, especially
when compared to COM components.You simply create a class that inherits from
System.Web.UI.Control or System.Web.UI.WebControls.WebControl and give it
whatever properties and methods you need. In Visual Studio .NET, you would normally
do this by creating a new Web Control Library project.You override its Render()
method to control its output, and you have a very simple yet powerful tool for encapsulating
and reusing user interface logic.
The code0301vb class is as follows:
Imports System.ComponentModel
Imports System.Web.UI
Namespace AspNetCookbook
<DefaultProperty(“Text”), ToolboxData(“<{0}:code0301vb
runat=server></{0}:code0301vb>”)> Public Class code0301vb
Inherits System.Web.UI.WebControls.WebControl
Dim _text As String
<Bindable(True), Category(“Appearance”),
DefaultValue(“”)> Property [Text]() As String
Get
Return _text
End Get
Set(ByVal Value As String)
_text = Value
End Set
End Property
Protected Overrides Sub Render(
ByVal output As System.Web.UI.HtmlTextWriter)
output.Write([Text])
End Sub
End Class
End Namespace
To reference a custom control on a Web Form, you need to add a Register directive to
the page, and specify three parameters.The TagPrefix is used for all controls from this
namespace and assembly when they are declared on the page, and can be anything but
asp, which is reserved for the built-in Web Controls that ASP.NET provides. Next, the
namespace in which the controls reside must be specified. Finally, the name of the
assembly, without any path information or the .DLL extension, is specified for the
Assembly parameter. An example of this follows:
<%@ Page language=”VB” %>
<%@ Register TagPrefix=”AspNetCookbook” Namespace=”AspNetCookbook”
Assembly=”codeVB” %>
...
<form id=”Form1” method=”post” runat=”server”>
<AspNetCookbook:code0301vb id=”code0301vb1” runat=”server” />
</form>

Note that in Visual Studio .NET, a default namespace with the same name as the project
is automatically prefixed to all Visual Basic class names.This is a frequent source of confusion
and is inconsistent with how default namespaces are handled in C#, where they
are inserted into each class file as a visible namespace.You can turn off this default
behavior by setting the default namespace to an empty string in the Project Properties
dialog box.You can determine the full namespace of a class by using the ILDASM.EXE
command-line tool on the generated assembly, or by going into the class view utility in
Visual Studio .NET.