4GuysFromRolla.com - ASP.NET Code Behind Pages

Windows Systems Administrator
Jupitermedia
US-CT-Darien

Published: Thursday, October 05, 2000

ASP.NET Code Behind Pages
By Mani Raja

- continued -

Learn More About ASP.NET!

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Even though ASP.NET is the next version of ASP, it is more than just a next version. ASP.NET is completely re-designed from the ground up and it provides a neat object oriented programming model. An ASP.NET page is an object derived from the .NET Page class. We all know that ASP.NET provides several new features and one of the important features is the separation of code and content.

In today's ASP application, we have a mix of HTML and Scripts making the code difficult to read, debug and maintain. ASP.NET relieves us from this problem by promoting the separation of code and content. That is, the user interface and the user interface programming logic need not necessarily be written in a single page. There are two ways in which you can separate the code and content:

As the title of the article indicates, I will explain the first mechanism that is used to neatly encapsulate the UI functionality in to a separate pre-compiled module. You will typically follow the steps below to develop an ASP.NET page that uses code-behind pages:

Now, we know that there are two separate files: one for the UI and the other for the UI logic. But, how do we relate these two files so that the ASP.NET page compiler will locate the code-behind file for the ASP.NET page. The glue between these two files is provided through the Page Directives, which are used to specify optional settings at the page level.

Creating the "Content"
Enough theory said about code-behind files. Let us get our hands on to the actual coding of a code-behind file. The ASP.NET page that displays the Web UI can be seen below. It uses a post-back form to query the user for username and information:

<%@ Page language="c#" Codebehind="CodeBehind.cs" Inherits="ASPPlus.CodeBehind" %> <HTML><BODY> <form action="CodeBehind.aspx" method=post runat="server"> <p align=center>Demonstration of Code Behind File</P> <p align=center><asp:Label id=Message runat="server"></asp:Label></P> <p> <h5>Sign-In Form</h5> Login: <asp:TextBox id=txtLogin Width=200 Runat=server /> <asp:RequiredFieldValidator ControlToValidate="txtLogin" Display="Static" Font-Name="verdana,arial,sans-serif" Font-Size="9pt" ErrorMessage="You must enter a Login." runat="server" ID="RFVLogin" /> <P> Password: <asp:TextBox id=txtPassword Width=200 Runat=server TextMode="Password" /> <asp:RequiredFieldValidator ControlToValidate="txtPassword" Display="Static" Font-Name="verdana,arial,sans-serif" Font-Size="9pt" ErrorMessage="You must enter a password." runat=server ID="RFVPassword"> </asp:RequiredFieldValidator> <P> <asp:Button id=btnSignIn Runat="server" Text="Sign In" onClick="btnSignIn_Click" /> </FORM> </body></html>

The first line of the ASP.NET page is the page directive that specifies the name of the code behind file and the actual class name inside that file. In our example, the file name is CodeBehind.cs and the class name is ASPPlus.CodeBehind.

<%@ Page language="c#" Codebehind="CodeBehind.cs" Inherits="ASPPlus.CodeBehind" %>

The namespace that I used for this code behind page is ASPPlus. Namespaces provide the naming scope for the classes and is very convenient way to represent hierarchy of classes. The rest of the code consists of HTML tags and Web Control declaration tags. The main thing to note down in this page is the ID properties of the controls. I will explain the importance of these IDs when we discuss the code-behind file.

In Part 2 we'll examine creating the complementing code for our .aspx page!

Read Part 2