Build Your Own ASP.NET 3.5 Website Using C# & VB (20 page)

creating “spaghetti” code—snippets of code that were scattered throughout the

presentation elements. This made it very tricky to manage the code between development teams, as you’ll know if you’ve ever tried to pick apart someone else’s ASP

code. In response to these problems, ASP.NET introduced a new development approach that allows code developers to work separately from the presentation designers who lay out individual pages. This new approach, called
code-behind
, keeps all of your presentational elements

(controls) inside the
.aspx
file, but moves all of your code to a separate class in a
.vb
or
.cs
code-behind file. Consider the following ASP.NET page, which displays a

simple button and label:

Visual Basic

LearningASP\VB\HelloWorld.aspx

<%@ Page Language="VB" %>

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87

"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

C#

LearningASP\CS\HelloWorld.aspx

<%@ Page Language="C#" %>

⋮

⋮

Let’s see how this example could be separated into the following distinct files:

HelloWorldCodeBehind.aspx

layout, presentation, and static content

HelloWorldCodeBehind.aspx.vb or HelloWorldCodeBehind.aspx.cs

code-behind files containing a custom page class

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Build Your Own ASP.NET 3.5 Web Site Using C# & VB

Since there isn’t a lot of code to type, you could create these files with any text editor, including Notepad. Visual Web Developer makes things easier for you, though. When adding a new Web Form file to the project, you have the option—which

you’ve already noticed when creating new pages—to
Place code in separate file
.

Create a new Web Form for your project by clicking
Website > Add New Item…
and

choosing the
Web Form
template. Check the
Place code in a separate file
checkbox, type
HelloWorldCodeBehind.aspx
for the file name, and click
Add
. The default code Visual Web Developer generates for the Web Form and its code-behind file is very

similar to the code of the
Default.aspx
form it created for your new Web Site project, back in
Chapter 1
.

We’ll start with the ASP.NET Web Form file
HelloWorldCodeBehind.aspx
. All we

have to do is change the page title and insert the ASP.NET controls—a Button and

a Label:

Visual Basic

LearningASP\VB\HelloWorldCodeBehind.aspx
(excerpt)

<%@ Page Language="VB" AutoEventWireup="false"

CodeFile="HelloWorldCodeBehind.aspx.vb"

Inherits="HelloWorldCodeBehind" %>

"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

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89

C#

LearningASP\CS\HelloWorldCodeBehind.aspx
(excerpt)

<%@ Page Language="C#" AutoEventWireup="true"

CodeFile="HelloWorldCodeBehind.aspx.cs"

Inherits="HelloWorldCodeBehind" %>

"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

As you can see, without code blocks, the main ASP.NET page becomes a bit simpler.

You might also notice that the only line that differs between these
.aspx
pages is the Page directive. Since the
.aspx
pages now contain only HTML layout, the contents

are identical no matter what language you use for the code.

You’ll also notice that the code-behind file (
HelloWorldCodeBehind.aspx.vb
or
Hello-
WorldCodeBehind.aspx.vb
) has been generated automatically, as it was for the
De-

fault.aspx
file back in Chapter 1. This is a pure code file, and contains no HTML or

other markup tags. Nevertheless, we can still access presentation elements from

this file, using their IDs (such as messageLabel).

Change the code to look like this:

Visual Basic

LearningASP\VB\HelloWorldCodeBehind.aspx.vb

Imports System

Imports System.Web.UI

Imports System.Web.UI.WebControls

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Build Your Own ASP.NET 3.5 Web Site Using C# & VB

Partial Class HelloWorldCodeBehind

Inherits System.Web.UI.Page

Sub Click(ByVal s As Object, ByVal e As EventArgs)

messageLabel.Text = "Hello World!"

End Sub

End Class

C#

LearningASP\CS\HelloWorldCodeBehind.aspx.cs

using System;

using System.Collections;

using System.Configuration;

using System.Data;

using System.Linq;

using System.Web;

using System.Web.Security;

using System.Web.UI;

using System.Web.UI.HtmlControls;

using System.Web.UI.WebControls;

using System.Web.UI.WebControls.WebParts;

using System.Xml.Linq;

public partial class HelloWorldCodeBehind : System.Web.UI.Page

{

protected void Page_Load(object sender, EventArgs e)

{

}

public void Click(Object s, EventArgs e)

{

messageLabel.Text = "Hello World!";

}

}

The code in the code-behind file is written differently than the code we’ve written

using