If you have been following from the beginning of this
article, you should have noticed how the concept of Application Services has
evolved. First of all, the Application Services were added to ASP.NET 2.0, and
after that AJAX developers were also able to access those Application Services
from the client-side. What are left are the Windows Forms and Windows
Presentation Foundation applications to access those Application Services and
this enables having a single database containing the entire user’s information
and shared by several application types including Web-AJAX and Windows
What can be understood is that Client Application Services
or CLAS, introduced with Visual Studio 2008 and .NET 3.5, is a way to allow a
Windows Forms or WPF application to access the Application Services using the
ASP.NET 2.0 AJAX 1.0 Extensions Application Services.
Usually, you would have a web application that is configured
with ASP.NET 2.0 Application Services and ASP.NET 2.0 AJAX 1.0 Extensions
Application Services and you need to use those application services in a new
Windows Forms application.
CLAS mainly gives the windows application the power of:
Authenticating and authorizing users: By configuring the
windows application to use the authentication service, the application can then
authenticate and authorize users against a database just as a Web or AJAX application can do.
Operating in an Offline-mode: What makes CLAS even more
powerful is that you can configure the application to cache all the processed
information while the application is in live connection to the database and
once the connection is off, the application can still operate in an offline
mode by retrieving information from the cached data. Usually, SQL Server
Compact Edition 3.5 database is used locally to store the information.
Visual Studio 2008 adds a new Tab to the project properties
page called Services and is shown in Figure 1.
Figure 1: Windows Forms Services Tab
This is a new Tab that has been added to allow you to
configure CLAS for your application. We will come to the above Tab later when
we go in depth into how to configure CLAS for an application.
CLAS is a collection of application services and is built on
top of several client application providers. For each of the services there is
a provider that can be configured through the app.config configuration file.
When you configure the application using the Services Tab,
automatically the configuration settings are added to the app.config file. Here
is a sample configuration setting.
System.Web.Extensions, Version=22.214.171.124, Culture=neutral,
credentialsProvider="ClientAppServicesDemo.Login, ClientAppServicesDemo" />
The above membership provider’s configuration section is so
close to the one we saw earlier when configuring the Membership provider in an
ASP.NET application. In the coming sections we will delve into more details
about the providers and classes that ship with the CLAS.