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Publisher2.1 Application Types
In
classic ASP, there was really only one type of applicationone
in which a client accessed a page with the .asp extension and in
which that page, either through embedded VBScript or JScript or
through script in combination with components built on
Microsoft's COM standard, returned HTML to the
browser to form the user interface with which the client would
interact. Clients typically interacted with the application only
through this user interface and did not have the option of creating
their own alternative interface to the functionality exposed by the
application.ASP.NET provides an enhanced version of this type of application,
which we'll discuss in the next section. ASP.NET
also introduces a new type of application, called a web service,
which provides clients the ability to use functionality exposed by an
application without being tied into that
application's user interface implementation.
2.1.1 ASP.NET Web Applications
The ASP.NET Web Application is the type of application
most developers will work with on a regular basis. The terminology
comes from the description used in the Visual Studio .NET environment
to describe the project type used to create this type of application.
You may also hear this type of application described as an ASP.NET
Web Forms Application. For reasons we'll explore in
the next chapter, we prefer the former term.An ASP.NET Web Application, in its simplest form, consists of a
directory made available via HTTP using the IIS administration tool or through the
Web Sharing tab of a
folder's Properties dialog (or by creating a web
application project in Visual Studio .NET) and at least one ASP.NET
page, designated by the .aspx file extension.
This file (or files), whose structure we'll discuss
in detail in the next chapter, typically contains a mix of HTML and
server-side code. This HTML and server-side code combine to create
the final output of the page, typically consisting of HTML markup
that is sent to the client browser. A simple ASP.NET page is shown in
Example 2-1.
Example 2-1. A simple ASP.NET page
<%@ Page Language="VB" %>
<html>
<head>
<title>Simple ASP.NET Page</title>
<script runat="server">
Sub Page_Load( )
Message.Text = "Hello, world!"
End Sub
</script>
</head>
<body>
<asp:Label id="Message" Runat="server"/>
</body>
</html>
The page shown in Example 2-1 simply executes the
code appearing in the <script
runat="server">, which uses an ASP.NET Label
control to display some text, along with the standard HTML tags that
are contained in the file. Figure 2-1 shows the output of the page as
viewed in Notepad by using the View Source option in Internet
Explorer. In this case, the Page_Load method (actually an event
handler, which we'll discuss more in later chapters)
sets the Text property of an ASP.NET Label control to
"Hello, world!". Because the Label
control will render its Text property to the browser automatically,
"Hello, world!" will appear in the
output that is sent to the browser, as shown in Figure 2-1.
Figure 2-1. Output of a simple ASP.NET page (source view)
Web Forms and Web ControlsExample 2-1 uses a control called the Label control to output text to the browser. This control is an example of what are referred to as Web Controls. Web Controls (also referred to as Server Controls), which are discussed in detail in Chapter 5, are compiled classes that run on the server and provide functionality similar to that of Windows controls such as textboxes, dropdown lists, etc. The key is that these controls run at the server, and so can be manipulated programmatically in server-side code.Web Form is a term used to describe an .aspx file that makes use of Web Controls. |
understanding that the code in a <script
runat="server"> block (or a
<% %> render block) is
executed on the serverafter the client requests the page, but
before the output of the page request is sent to the client browser.
This allows developers to decide, based on the code they write and
the input received from the user, just what output actually is sent
to the browser, either directly (such as by calling the Write method
of the Response object) or by manipulating controls, as shown in
Example 2-1. It also allows additional
functionality, such as server-side state management, to be provided
to these applications.Besides the containing directory and ASP.NET file(s), an ASP.NET Web
Application may also contain configuration files
(web.config ), User Control files
(.ascx ), and an application settings file
(Global.asax ), as well as code-behind, assembly,
and class files that provide additional functionality to the
application. We'll discuss each of these file types
later in this chapter.
2.1.1.1 ASP.NET Mobile Web Applications
The ASP.NET Mobile Web Application is a subtype of Web Application
specific to developing for mobile devices such as cell phones and
PDAs. The primary thing that distinguishes a mobile web application
from a standard web application in ASP.NET is the use of the ASP.NET
mobile controls, which are built into the .NET Framework as of
Version 1.1. These include the mobile Form control and standard
controls such as labels, textboxes, and panels, as well as
mobile-specific controls such as the TextView, PhoneCall, and
SelectionList controls. Note that both mobile Web Forms pages (those
that use the mobile controls) and standard Web Forms pages can
coexist within the same application, if desired.To simplify development of ASP.NET applications for mobile devices,
Visual Studio .NET 2003 provides an ASP.NET Mobile Web Application
project template. This template includes a default mobile Web Form,
as well as a special section added to the
Web.config file called
<deviceFilters>, which contains settings for
device-specific rendering.
2.1.2 ASP.NET Web Services
The
other type of application available to ASP.NET developers is the
ASP.NET Web Service. Like ASP.NET Web Applications, there are a
number of terms floating around for this type of application.
(Microsoft refers to web services as "XML Web
Services," perhaps in hopes of a positive
association between web services and the XML standard.) A
web service is an
application that exposes programmatic functionality to clients over
the Internet or an intranet using the underlying plumbing of a
developing W3C standard called SOAP. In simple terms, it can be seen
as a simple function call across the Internet.
What Is SOAP?The proposed SOAP standard, which at the time of this writing was a W3C Candidate Recommendation (see http://www.w3.org/Consortium/Process-20010719/trl#RecsCR for information on where this fits in the standardization process) and versioned at 1.2, describes a protocol that may be used within the framework of HTTP (other transport protocols are possible, but the SOAP specification does not define how to use them) to send and receive requests and responses consisting of either specific data or remote procedure calls and responses, or both. The SOAP specification defines the format for messages sent via SOAP, methods for communicating how a message should be processed, and encoding rules for communicating data types across heterogeneous platforms.Assuming that the proposed SOAP standard is adopted as a W3C Recommendation (recommendation is the term used by the W3C to describe stable standards such as HTML 4.01; see http://www.w3.org for more information on current recommendations), application developers on a given platform can expose their functionality to others on different platforms in a fashion that makes the differences in platform transparent. As long as both the server and the client follow the SOAP specification, the applications can communicate, regardless of the platform differences.Since SOAP has not yet been adopted as a recommendation and is still under development, current implementations from Microsoft and other vendors have not yet achieved the level of cross-platform interoperability that is promised once SOAP is adopted as a recommendation. As such, you should take the time to test and evaluate the interoperability of your chosen platform(s) before committing substantial resources to web services, if you are planning to use web services to facilitate cross-platform interoperability. |
made available via HTTP using the IIS administration tool or through
the Web Sharing tab of a folder's Properties dialog
(or by creating a Web Application project in Visual Studio .NET) and
at least one web service file, designated by the
.asmx file extension.
Unlike an ASP.NET page, this file (or files), whose structure
we'll discuss in detail in Chapter 4, typically does not contain HTML, but
consists solely of server-side code. The methods to be exposed by the
web service carry the WebMethod attribute
(note that the syntax of the WebMethod attribute
varies depending on the language used). A simple web service is shown
in Example 2-2.
Example 2-2. A simple web service
<%@ WebService Language="VB" Class="Hello" %>
Imports System
Imports System.Web.Services
Public Class Hello : Inherits WebService
<WebMethod( )> Public Function SayHello( ) As String
Return("Hello, World!")
End Function
End Class
If the .asmx file that makes up this web service
is called from a browser, ASP.NET will output a page that documents
how the web service should be called, and also provides the ability
to test the invocation of the web service. This page is shown in
Figure 2-2.
Figure 2-2. Output of a simple web service
When invoked, the web service shown in Example 2-2
will return "Hello, World!" as an
XML-formatted response, according to the SOAP 1.1 specification, as
shown here:
<?xml version="1.0" encoding="utf-8" ?>
<string xmlns="http://tempuri.org/">Hello, World!</string>
The documentation page provided by ASP.NET also allows you to review
the Web Service Description Language (WSDL) description of your web
service. WSDL, which we'll discuss further in Chapter 4, is an XML-based format for describing the
functionality exposed by a web service, including the format and data
type of input and output parameters, and can be considered a contract
for how clients interact with the web service. In this way, WSDL
plays a role similar to that of Interface Description
Language (IDL) in Microsoft's COM component
specification.
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