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

This article was previously published under Q303247
This article refers to the following Microsoft .NET Framework Class Library namespace:
  • System.Web.UI

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


ASP.NET supports two methods to author pages:
  • In-line code
  • Code-behind

In-Line Code

In-line code is code that is embedded directly within the ASP.NET page. The following code represents a sample ASP.NET page that includes in-line code:

<%@ Language=C# %>
   <script runat="server" language="C#">
   void MyButton_OnClick(Object sender, EventArgs e)
      MyLabel.Text = MyTextbox.Text.ToString();
      <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_OnClick" runat="server"></asp:button>
         <asp:label id="MyLabel" runat="server"></asp:label>


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:

<%@ Language="C#" Inherits="MyStuff.MyClass" %>
        <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" />
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).

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.


For additional information%1, click the article number%2 below to view the article%2 in the Microsoft Knowledge Base:
313105  ( ) BUG: Cannot Compile Code-Behind Files That Use Src Attribute on a UNC Share

  • Microsoft ASP.NET 1.1
  • Microsoft ASP.NET 1.0
kbinfo kbwebforms KB303247
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