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Creating ASP.NET Web Services, Part 1
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The WebMethod attribute

Related Reading

Programming .NET Web Services
By Alex Ferrara, Matthew MacDonald

The HelloWorldService class exposes a single method, the public method HelloWorld, which takes no arguments and returns a string containing the text "Hello World". To expose a method as a part of a web service, you must decorate it with the WebMethod attribute, which tells the compiler to treat it as such. Any method marked with the WebMethod attribute must be defined as public. Class methods exposed as web services follow the same object-oriented rules as any other class, and therefore methods marked private, protected, or internal are not accessible and will return an error if you attempt to expose them using the WebMethod attribute. For additional details, see "The WebMethod Attribute" later in this chapter.



The neat thing about this simple example is that you've created a full-blown web service out of an arbitrary method. You could just as easily have substituted a method that retrieves a record from a data store or a method that wraps a COM object. Additionally, you could have used any of the languages supported by the .NET Framework for this implementation and, then, as you will see later, used any .NET or non-.NET language in a client application. By inheriting from the System.Web.Services.WebService class, you are able to take advantage of an API that insulates you from the underlying SOAP/XML message exchanges.

To put this web service to work, all you need to do is copy it to the web server just as you would any other resource, whether it's an image, HTML file, ASP page, or another resource. Once you've done that, the web service is ready to be used by a consumer application, a process we'll look at in detail in Chapter 3. This ease of deployment is the main benefit of inline coding; perhaps the biggest drawback is that your presentation code and business logic are lumped into the same file, which can make working with large projects difficult to manage. Let's take a look at how Visual Studio .NET can be used to create and deploy this web service without stepping outside its Integrated Development Environment by using the so-called code-behind approach.

Assemblies

We said that a namespace is a container for types such as classes, interfaces, structs, and enums. We also said that the source code for objects in a namespace does not have to be stored in the same file, but can instead span multiple files. When the set of source code constituting a namespace is compiled into a library, this library is called a managed DLL, or, more commonly, an assembly. Assemblies are the building blocks of .NET applications and the fundamental unit of deployment. They comprise a collection of types and resources that provide the CLR (Common Language Runtime) with the information it needs to be aware of type implementations. Their contents can be referenced and used by other applications using Visual Studio .NET or a .NET command-line compiler.

Creating "Hello, World" with Visual Studio .NET

While Notepad is an adequate tool for creating simple services, Microsoft's new development environment, Visual Studio .NET (VS.NET), provides a world of features to aid you in creating complex web services. Visual Studio .NET also provides the quickest path to getting a web service up and running, apart from the time it takes to install all or part of the more than 1.8 GB (compressed) of installation files required to run Visual Studio .NET. This section takes you through the process of creating the "Hello, World" service using Visual Studio .NET.

Setting up VS.NET for the web service project

To make use of the automation in VS.NET, you must first configure it to communicate with your web server. You can use either FrontPage Extensions or Universal Naming Convention (UNC) file shares. To keep things simple, we'll assume you have installed IIS on your local workstation. Here's what you need to do to set up VS.NET for your first web service. We go into detail on FrontPage Extensions and UNC file shares later in this chapter (see "Deploying a Web Service.")

Microsoft FrontPage Server Extensions are the easiest to configure and a good choice for the simple web services in the next two chapters. FrontPage Extensions can be installed as a part of IIS, or alternatively downloaded for free from the MSDN site at http://msdn.microsoft.com. For this example, we're using a Windows 2000 workstation, IIS 5, and FrontPage 2000 Server Extensions, version 4.0.2.4426. While any version of the Extensions will work, the configuration process varies greatly among them and the steps outlined here may not work with your version.

Once you've installed FrontPage Server Extensions on your local workstation (i.e., the workstation hosting IIS), open the Internet Services Manager from the Start -> Programs -> Administrative Tools menu so that you can configure a FrontPage web. Right-click on Default Web Site and select All Tasks -> Configure Server Extensions from the dialog box. You will be taken through a brief configuration wizard that asks you configuration questions. Once the server extensions have been installed, you're ready to create a web service project in Visual Studio .NET.

TIP: With Windows XP, you reach Administrative Tools and the IIS Manager through he Control Panel.

Creating a C# web service project

Visual Studio 6.0 users will find the layout of Visual Studio .NET familiar enough that they can get working without much assistance. We'll help users who are new to Visual Studio. Users new to Visual Studio .NET can also rely on its extensive built-in Help feature.

To create a new web service, fire up Visual Studio .NET and either select the New Project button on the default Start Page or click File -> New -> Project on the main Visual Studio .NET menu bar. The Visual Studio project model is the same as earlier versions, in that a file can be part of a project, and a project part of a solution. A solution is the outermost container, containing zero or more projects. After selecting an option to create a new project, you'll see the screen in Figure 2-1.

Figure 2-1. Creating a new Visual Studio project

Figure  

Here you have the option to create a variety of project types from templates. Under Visual C# Projects, one template option creates an ASP.NET web service, while our examples use the C# language, the same option also available as a Visual Basic project, and similar options for Managed C++ exist as well. In addition to selecting a project language and template, you must specify a project name and location. The location fior the HelloWorldService should be the URL of the IIS web server you just configured to work with FrontPage Extensions (e.g., http://localhost). For this example, we'll use the project name "HelloWorldService."

Once you click OK, the IDE (Integrated Development Environment) creates a new solution and project and automatically populate the project with several files. The IDE will also create a virtual folder under IIS with the same name as the project name, which, in this case, is HelloWorldService.

Exploring the solution and project

The contents of your new project are displayed in the Solution Explorer window, which should appear on the right side of the VS.NET IDE, as shown in Figure 2-2.

Figure 2-2. The Visual Studio .NET Solution Explorer

Figure  

If the Solution Explorer is not visible, you can open it by selecting Solution Explorer from the View menu (or pressing Ctrl-Alt-L).

When you create a new project without specifying the name of an existing solution, VS.NET creates a new solution whose name is the same as the one you chose for your project. You can see in Figure 2-2 that, in this case, a solution named HelloWorldService has been created; it contains one project, also called HelloWorldService.

Visual Studio .NET also automatically creates several assembly references and files, which are also displayed in the Solution Explorer, as shown in Figure 2-3. In this example, VS.NET has included assembly references to the System, System.Data, System.Web, System.Web.Services, and System.XML namespaces. (The System.Data and System.XML assembly references are not necessary for this example, so you can remove them if you'd like, but there's no real benefit to doing so other than simplicity.)

Figure 2-3. Displaying all files in VS.NET Solution Explorer

Figure  

The five other files that appear in Figure 2-3 are AssemblyInfo.cs, Global.asax, HelloWorldService.vsdisco, Service1.asmx, and Web.config. The only file you really need to create the web service is the .asmx file, which we'll discuss in the next section. The four other files provide additional features and functionality that will help you as you build more complex services, but none of them are necessary for this example. In fact, you can delete all of the non-.asmx files and the service will run just fine (we don't recommend this). Here's a brief explanation of of each of these.

AssemblyInfo.cs
An information file that provides the compiler with metadata (name, version, etc.) about the assemblies in the project.
Global.asax
Customizable to handle application-level events (e.g., Application_OnStart).
HelloWorldService.vsdisco
An XML file used for dynamic discovery of web services. The DISCO specification has been superseded by WS-Inspection and is discussed in Chapter 10.
Web.config
An XML file containing configuration information for the application.

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