Article ID: 303247 - Last Review: February 23, 2007 - Revision: 3.4

INFO: ASP.NET Code-Behind Model Overview

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This article was previously published under Q303247

This article refers to the following Microsoft .NET Framework Class Library namespace:

System.Web.UI

SUMMARY

This article provides a brief overview of the code-behind model, which is introduced in ASP.NET.

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Code-behind refers to code for your ASP.NET page that is contained within a separate class file. This allows a clean separation of your HTML from your presentation logic. The following sample illustrates an ASP.NET code-behind page:

MyCodebehind.aspx

<%@ Language="C#" Inherits="MyStuff.MyClass" %>
<HTML>
    <body>
        <form id="MyForm" runat="server">
        <asp:textbox id="MyTextBox" text="Hello World" runat="server"></asp:textbox>
        <asp:button id="MyButton" text="Echo Input" Onclick="MyButton_Click" runat="server"></asp:button>
        <asp:label id="MyLabel" runat="server" />
        </form>
    </body>
</HTML>

Mycodebehind.cs

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

namespace MyStuff
{
    public class MyClass : Page
    {
        protected System.Web.UI.WebControls.Label MyLabel;
        protected System.Web.UI.WebControls.Button MyButton;
        protected System.Web.UI.WebControls.TextBox MyTextBox;

        public void MyButton_Click(Object sender, EventArgs e)
        {
            MyLabel.Text = MyTextBox.Text.ToString();
        }
    }
}

In the preceding sample, you can use the following syntax to compile Mycodebehind.cs:

csc.exe /out:mycodebehind.dll /t:library mycodebehind.cs

When you use the following code, the code-behind page inherits from the Page class. The Page class resides in the System.Web.UI namespace:

public class MyClass : Page

Inheriting from the Page class gives the code-behind page access to the ASP.NET intrinsic objects, such as Request and Response. In addition, inheriting from the Page class provides a framework for handling events for controls within the ASP.NET page.

In the preceding sample, the code-behind page is compiled before ASP.NET runs. Alternatively, you can reference the code-behind class by using an SRC tag as follows:

<%@ Language="C#" Inherits="MyStuff.MyClass" src="MyCodebehind.cs" %>

In this case, ASP.NET compiles the code-behind page on the fly. Notice that this compilation step only occurs when the code-behind file is updated (which is detected through a timestamp change).

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Code-Behind Support in Visual Studio .NET

When you use Microsoft Visual Studio .NET to create ASP.NET Web Forms, code-behind pages are the default method. In addition, Visual Studio .NET automatically performs precompilation for you when you build your solution. Note that code-behind pages that are created in Visual Studio .NET include a special page attribute, Codebehind, which Visual Studio .NET uses.

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