Mastering Visual Basic .NET

ASP was limited to the HTML controls. ASP.NET uses a new family of controls, the Web controls.
The Web controls exist on the server, and you can program against them, just as you program
Windows controls. Your code resides on the server and manipulates Web controls. When it’s time
to send a response to the client, ASP.NET translates the Web controls into HTML controls and
HTML code, and sends to the client a page that can be rendered by the browser. As you will realize
after reading this and the following chapter, ASP.NET abstracts much of the mundane tasks of
client/server interaction and makes the process look like programming a Windows application.
I should clarify this point for the benefit of readers who are already familiar with ASP. If you’re new
to Web programming, please bear with me. Before you reach the end of this chapter, everything will
make perfect sense. With ASP, the browser submits the contents of the controls on the current page to
the server when a special button is clicked, the Submit button. This button may be named anything: Go,
Show Results, Place Order, whatever. The HTML code of the page uses a Submit button to send the
data on the current page to the server (or post the page back to the server, as this process is known).
The ASP script on the server knows the names of the controls on the page and must extract their
values from the QueryString property of the Request object. If the page being submitted contains
two Text controls, named ProdID and Quantity, it must use the following statements to extract the
values on these two controls:
ProductID = Request.QueryString(“ProdID”)
Quantity = Request.QueryString(“Quantity”)
Then, it must process them (retrieve the price of the specified product from a database, multiply
it by the quantity ordered, and apply some discount) and create a page to send to the client. The
page is created by sending HTML code to the client through the Write method of the Response
object:
Response.Write “Thank you for ordering”
Response.Write “Your total is “ & price * Quantity
where price is a variable that holds the product’s price (I’m not showing the code that retrieves this
value from the database).
With ASP.NET, you can use the TextBox Web control, which is very similar to the
Windows TextBox control. Let’s say that the names of the two TextBoxes are ProdID and Quantity,
and that the form also contains a Label control. To program the application, you double-click the
Submit button and insert the following statements in its Click event handler:
Label1.Text = “Thank you for ordering” & vbCrLf
Label1.Text = Label1.Text & “Your total is “ & price * Quantity.Text
AN HTML PRIMER
This is VB.NET code, which will be compiled and executed on the server. You don’t have to use the
Request object to retrieve the values of the TextBox controls, and you don’t have to use the Response
object to create a new page. The results of the processing are placed on a Label control on the current
form, which is then sent to the client. Obviously, ASP.NET parses the data submitted by the client
through the QueryString object and makes them available to your code as control properties.
In short, ASP.NET is a vastly improved version of ASP, abstracting many of the tasks in
client/server interaction. It makes the whole process look like a Windows application to the developer,
but behind the scenes it generates the HTML that will produce the desired page on the client.
This page contains straight HTML code.
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