Web Controls

There are two ways you can create your own controls in ASP.NET. The first is known as custom controls, and is accomplished by creating a class deriving from either System.Web.UI.Control or System.Web.UI.WebControls.WebControl. The latter derives from the former, and adds additional UI properties to the class. The other method is to create what is known as a user control, which is very similiar to an ASP.NET page, but has an .ascx extension.

Web Custom Controls

As previsouly mention, System.Web.UI.Control and System.Web.UI.WebControl are base classes for custom controls. For your control to be useful, you are probably going to want to render some HTML to the browser. This is accomplished by overriding the Control's Render method. An HtmlTextWriter parameter gives you access to the output stream.

The following is a barebones custom control. Notice how the Render method is

using System;
using System.Web.UI;
using System.Web.UI.WebControls;

namespace WebCustomControl
{
     public class FirstControl : Control
     {
            protected override void Render( HtmlTextWriter writer)
            {
             writer.Write("Hello World");
            }
     }
}

To use this control in a page, you need to register it with a Register directive. The following ASP.NET page registers and uses the barebones control.

<%@ Register TagPrefix="Custom" Namespace="WebCustomControl" Assembly="WebCustomControl" %>
<html>
<body>
     <form runat="server">
        Most introductory applications output:
        <Custom:FirstControl runat="server" />
     </form>
</body>
</html>

Web User Controls

Web User Controls are very much like ASP.NET page snippets. Like an ASPX page, you can open them in design view, and add additional controls and HTML. They are registered similiarly to Web Custom Controls. Using the Visual Studio.NET IDE, you can drag an ascx control onto an ASP.NET page, and Visual Studio.NET will take care of the registration and implementation tag for you. The following is an example of a Web User Control.

<%@ Control Language="c#" AutoEventWireup="false" Codebehind="header.ascx.cs" Inherits="DotnetCoders.Web.header" %>

Hello World!

Here is an HTML page utilizing the Web User Control.

<%@ Page language="c#" %>
<%@ Register TagPrefix="Custom" TagName="FirstControl" Src="~/header.ascx" %>
<html>
<body>
     <form runat="server">
        Most introductory applications output:
        <Custom:FirstControl runat="server" />
     </form>
</body>
</html>