dot.NET.Framework.Essentials.1002003,.3Ed [Electronic resources] نسخه متنی

7.6 ASP.NET and Web Services

The
ASP.NET framework simplifies development of web services.[7] All the low-level work, such as packaging
and unpackaging data in XML format and utilizing HTTP protocol to
transport the web messages between distributed components, are done
by the framework. This allows the developers to focus on the
application logic.

Chapter 6. This section reviews web services briefly to
remind you that the underlying support for web services is
ASP.NET.

The .NET Framework uses asmx as the default file
extension for web services, as opposed to aspx
for Web Forms and ascx for web controls.

7.6.1 The WebService Directive

All asmx files start with
the
@WebService directive that instructs ASP.NET on
how to compile the code, as well as the main class name. The
WebService directive has the following attributes:

Language

Specifies the language in which the code was
written. This instructs the ASP.NET framework to use the appropriate
compiler to build your web service. Use VB for
Visual Basic, C# for C#, and JS
for JScript .NET. As other languages emerge, obviously you can
specify other languages.

Class

Specifies the main class, which exposes web methods. The
ASP.NET framework instantiates this class in order to serve the web
methods to the clients.

Codebehind

Specifies the source file for your code, which
allows for complete code/ASP separation.

You can easily create a simple Web Service similar to the following
asmx file:

<%@ WebService Language="VB" class="MathClass" %>
imports System.Web.Services
Public Class MathClass
<WebMethod> _
public function Add(a as integer, b as integer) as integer
return(a + b)
end function
end class

Note the line continuation symbol right after
<WebMethod>. If you prefer to separate your
code completely from any ASP.NET elements, you could have the code
for your Web Service saved in a separate file and specify the
Codebehind attribute of the
@WebService directive to point to the code file:

<%@ WebService Language="VB" Codebehind="MathClass.vb" Class="MathClass" %>

The source for MathClass.vb looks exactly like
the asmx shown earlier minus the first line. You
can use the following command line to compile
MathClass.dll:

vbc /t:library /r:System.Web.Services.dll MathClass.vb

As with all code-behind, the binary has to be deployed in the
/bin directory under the application.

7.6.2 The WebMethod Attribute

Public methods of any classes can be tagged
with the WebMethod attribute to be made accessible from the Web. The
syntax for tagging attributes to methods is different for each .NET
language. For example, in C# the tag takes the following form:

[WebMethod(attribute="value" attribute="value" . . . )]
public returnType FunctionName(paramsList)

In VB, angle brackets are used instead of square brackets and the
assignment symbol is ":=" instead
of just "=". Also note that the
whole web method declaration is on a single line. If you want to
separate them for readability, use the line continuation symbol
"_":

<WebMethod(attribute:="value" attribute="value" . . . )> Public Function
FunctionName(paramsList) as returnType
<WebMethod(attribute:="value" attribute="value" . . . )> Public Sub
SubName(paramsList)

7.6.3 Using Web Services

If you are
using Visual Studio .NET, you can choose
Project/Add Web Reference and then type in the URL where the Web
Service resides.[8] For our purpose,
we'll point to the Web Service we created in the
last chapter, PubsWS. The URL to this Web Service on our server is
http://localhost/PubsWS/PubsWS.asmx. The default
web reference name is the server name where the Web Service was
found. After adding the web reference, you can access the proxy
object to the Web Service you are calling via the type
servername.proxyObjectName. For your case, it is
localhost.PubsWS.[9]

[8] In VS.NET 1.1, you can also browse
the web services on your local machine in addition to browsing web
services on UDDI servers.

[9] You can rename
the web reference when adding it to your project. This way the Web
Service will be
<yourwebservicename>.proxyObjectName
instead of
servername.proxyObjectName.

The following code excerpt demonstrates how to use the Web Service
through the proxy. We create an instance of the proxy object and then
ask it to relay the message to the real Web Service to get the list
of authors. The result will be streamed back in XML format, which is
reconstructed into a DataSet object. We then bind
DataGrid1, which is just a DataGrid object that we
have on the Web Form, to the default view of the first table of the
DataSet. Finally, we ask for the actual binding to take place. The
resulting page is the grid populated with rows from the Authors table
of the Pubs sample database:

localhost.PubsWS ws = new localhost.PubsWS( );
DataSet ds = ws.GetAuthors( );
DataGrid1.DataSource = ds.Tables[0].DefaultView;
DataGrid1.DataBind( );

Instead of using Visual Studio .NET to locate and automatically
generate the proxy class, you can also use the information from the
previous chapter to generate the source for the proxy class yourself.
You can then include or compile the source into a DLL and add the DLL
to the project as a reference. In any case, the end result is the
same. Here is an example that links against the proxy we created in
the previous chapter and fills a grid with data:

<%@ Page Language="C#" %>
<%@ Import Namespace="System.Data" %>
<!-- Link to the proxy generated by wsdl.exe -->
<%@ Assembly Src=" %>
<html>
<head>
<title>SOAP Client</title>
</head>
<body>
<!-- Make the SOAP call and fill the data grid. -->
<%
PubsWS ws = new PubsWS( );
DataSet ds = ws.GetAuthors( );
dg.DataSource = ds.Tables[0].DefaultView;
dg.DataBind( );
%>
<!-- Create a data grid. -->
<asp:DataGrid id="dg" runat="server"/>
</body>
</html>