Build Your Own ASP.NET 3.5 Website Using C# & VB (10 page)

for real. To see your dynamically generated web page content in all its glory, hit
F5

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Introducing ASP.NET and the .NET Platform

19

to execute the project again, and see the current date and time, as depicted in Fig-

ure 1.16
.

Figure 1.16. Loading
Default.aspx
with a Label element with dynamically generated content Both versions of the page achieve exactly the same thing. You can even save them

both, giving each a different filename, and test them separately. Alternatively, you

can create two Visual Web Developer projects—one for C# code, in
C:\Learnin-

gASP\CS
, and one for VB.NET code, in
C:\LearningASP\VB
.

No Time?

If the time isn’t displayed in the page, chances are that you opened the file directly

in your browser instead of loading it through your web server. Because ASP.NET

is a server-side language, your web server needs to process the file before it’s sent

to your browser for display. If it doesn’t gain access to the file, the ASP.NET code

is never converted into HTML that your browser can understand, so make sure

you load the page by executing it in Visual Web Developer. Loading the page in

your browser directly from Windows Explorer will not execute the code, and

consequently the time won’t display.

So how does the code work? Let’s break down some of the elements that make up

the page. We’re defining a method called Page_Load, in both languages:

Visual Basic

LearningASP\VB\Default.aspx.vb
(excerpt)

Protected Sub Page_Load(ByVal sender As Object,

➥ ByVal e As System.EventArgs)

Handles Me.Load

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

C#

LearningASP\CS\Default.aspx.cs
(excerpt)

protected void Page_Load(object sender, EventArgs e)

{

I won’t go into too much detail here. For now, all you need to know is that you can

write script fragments that are run in response to different events, such as a button

being clicked or an item being selected from a drop-down. What the first line of

code basically says is, “execute the following script whenever the page is loaded.”

Note that C# groups code into blocks with curly braces ({ and }), while Visual Basic

uses statements such as End Sub to mark the end of a particular code sequence. So,

the curly brace ({) in the C# code above marks the start of the script that will be

executed when the page loads for the first time.

Here’s the line that actually displays the time on the page:

Visual Basic

LearningASP\VB\Default.aspx.vb
(excerpt)

myTimeLabel.Text = DateTime.Now.ToString()

C#

LearningASP\CS\Default.aspx.cs
(excerpt)

myTimeLabel.Text = DateTime.Now.ToString();

As you can see, these .NET languages have much in common, because they’re both

built on the .NET Framework. In fact, the only difference between the ways the two

languages handle the above line is that C# ends lines of code with a semicolon (;).

In plain English, here’s what this line says:

Set the Text of myTimeLabel to the current date and time, expressed

as text

Note that myTimeLabel is the value we gave for the id attribute of the

tag where we want to show the time. So, myTimeLabel.Text, or the Text property

of myTimeLabel, refers to the text that will be displayed by the tag. DateTime is a

class that’s built into the .NET Framework; it lets you perform all sorts of useful

functions with dates and times. The .NET Framework has thousands of these classes,

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Introducing ASP.NET and the .NET Platform

21

which do countless handy things. The classes are collectively known as the
.NET

Framework Class Library
.

The DateTime class has a property called Now, which returns the current date and

time. This Now property has a method called ToString, which expresses that date

and time as text (a segment of text is called a
string
in programming circles). Classes, properties, and methods: these are all important words in the vocabulary of any

programmer, and we’ll discuss them in more detail a little later in the book. For

now, all you need to take away from this discussion is that DateTime.Now.ToString() will give you the current date and time as a text string, which you can then tell your tag to display.

The rest of the script block simply ties up loose ends. The End Sub in the VB code,

and the } in the C# code, mark the end of the script that’s to be run when the page

is loaded:

Visual Basic

LearningASP\VB\Default.aspx.vb
(excerpt)

End Sub

C#

LearningASP\CS\Default.aspx.cs
(excerpt)

}

One final thing that’s worth investigating is the code that ASP.NET generated for

you. It’s clear by now that your web browser receives only HTML (no server-side

code!), so what kind of HTML was generated for that label? The answer is easy to

find! With the page displayed in your browser, you can use the browser’s
View Source

feature to view the page’s HTML code. Here’s what you’ll see:

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

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

Notice that all the ASP.NET code has gone? Even the tag has been

replaced by a tag (which has the same id attribute as the tag we used) that contains the date and time. There’s a mysterious hidden input element

named __VIEWSTATE that is used by ASP.NET for certain purposes, but we’ll ignore

it for now. (Don’t worry, we’ll discuss it a bit later in the book!)

That’s how ASP.NET works. From the web browser’s point of view, there’s nothing

special about an ASP.NET page; it’s just plain HTML like any other. All the ASP.NET

code is run by your web server and converted to plain HTML that’s sent to the

browser. So far, so good, but the example above was fairly simple. The next chapter

will get a bit more challenging as we investigate some valuable programming concepts.

Getting Help

As you develop ASP.NET web applications, you’ll undoubtedly have questions that

need answers, and problems that need to be solved. Help is at hand—Microsoft has

developed
the ASP.NET support web site.
2 This portal provides useful information for the ASP.NET community, such as news, downloads, articles, and discussion

2 http://www.asp.net/

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Introducing ASP.NET and the .NET Platform

23

forums. You can also ask questions of the experienced community members in the

SitePoint Forums.3

Summary

In this chapter, you learned about .NET. You also learned of the benefits of ASP.NET,

and that it’s a part of the .NET Framework.

First, you learned about the components of ASP.NET. Then we explored the software

that’s required not only to use this book, but also in order for you or your company

to progress with ASP.NET development.

You’ve gained a solid foundation in the basics of ASP.NET! The next chapter will

build on this knowledge as we begin to introduce you to ASP.NET in more detail,

covering page structure, the languages that you can use, various programming concepts, and the finer points of form processing. 3 http://www.sitepoint.com/forums/

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ASP.NET Basics

So far, you’ve learned what ASP.NET is, and what it can do. You’ve installed the

software you need to get going, and you even know how to create a simple ASP.NET

page. Don’t worry if it all seems a little bewildering right now, because, as this book

progresses, you’ll learn how easy it is to use ASP.NET at more advanced levels.

As the next few chapters unfold, we’ll explore some more advanced topics, including

the use of controls, and various programming techniques. But before you can begin

to develop applications with ASP.NET, you’ll need to understand the inner workings

of a typical ASP.NET page—with this knowledge, you’ll be able to identify the parts

of the ASP.NET page referenced in the examples we’ll discuss throughout this book.

So in this chapter, we’ll talk about some key mechanisms of an ASP.NET page,

specifically:

■ page structure

■ view state

■ namespaces

■ directives

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

We’ll also cover two of the “built-in” languages supported by the .NET Framework:

VB and C#. As this section progresses, we’ll explore the differences and similarities