ASP.NET in a Nutshell

Consuming a Web Service

In ASP.NET, consuming a web service is nearly as easy as creating one. ASP.NET provides a utility called wsdl.exe that can create a proxy class, which is a class that knows all of the necessary details of communicating with the web service via SOAP, as shown in Figure 4-1, and which can be called from a client application the same way as any other managed class, In this way, the proxy class abstracts away the complexities of communication with the web service.

Consuming a web service in ASP.NET requires four steps:

1. Locate the WSDL contract for the desired web service.

2. Create a proxy class by using the wsdl.exe command-line utility.

3. Compile the proxy class.

4. Create a new instance of the proxy class in the client application (WinForms, Console, or ASP.NET) and call the desired methods.

In the case of our Qotd_cb web service, you would execute the following command (again, conveniently saved as a DOS batch file) to generate a proxy class based on the web service:

wsdl /l:vb /out:Qotd_cb_proxy.vb http://localhost/ASPdotNET_iaN/Chapter
_4/Qotd_cb.asmx?WSDL
  
pause

The /l parameter specifies that the proxy class should be generated in Visual Basic .NET (the default is C#). The /out parameter specifies the name and, optionally, the path of the output file. This is important if you are compiling your proxy class in the same directory as the code-behind class that implements the web service. In this case, if you do not specify the output filename, the file Qotd_cb.vb will ...