Creating Web Services Using ASP.NET AJAX

Web services are applications through which one can provide different kinds

of online services to the web user. These services are hosted on the Internet

and can be accessed by authorized users to embedded on their web site. There are

a number of web service providers such as Google that provide a host of web

services: for eg, the Google search engine can be incorporated into your web

site. Windows Live is another such service that lets you incorporate Windows

Live Services to your web site, Windows Live Contact Service shows users'

contact list, Windows Live Messenger allows for chatting within the Internet

browser and authentication with Windows Live ID. Another example is 'Amazon.com'

that allows you to develop a customized application which can search details of

products without even visiting the website.

So, why should you implement web services within your website. Well, they

reduce your time and effort spent in doing the same job twice and making things

a lot easier for visitors to the website. For example if you want to show the

local weather report on your website it won't be feasible for you to stand under

the open sky and study weather patterns. On top of it, you'll have to update the

temperature continuously on your web site. So, what you can do instead is to

have a weather status widget on your website so that you can use the service

provided by any weather reporting website to your own website.

Likewise you can have a currency converter within your website which takes

the currency value right from the local stock exchange. Web Services works on

three different platforms:

1. SOAP: Simple Object Access Protocol is based on XML and is both

language and platform independent.

2. WSDL:Web Service Description Language which is also based on the

XML but is basically used to describe the web service and how you can access it.

3. UDDI: Universal Description, Discovery and Integration is a

directory service that is used where one can register and then search for web

services. UDDI uses SOAP to communicate and is built into the MS .NET platform.

Now let's see how you can make your own web service in ASP.NET AJAX and also

how you can make use of it at the client side. For creating this we shall use

Visual Web Developer 2008. Start with creating a new web service and click on

File > New Web Site and select the ASP.NET web service template. Now click on

the browse button. Select the local IIS tab on the left hand side and then add a

new web service to it.

Give a meaningful name to the web service and click on 'Ok'. As soon as the

development environment gets ready, you shall see a web service automatically

created. Delete the pre-created service and start the process for creating your

own web service. For deleting, right click on the 'service.asmx' file listed on

the right side; also delete the code associated with 'service.asmx', i.e. the

'service.vb' file. Now create a new web service by right clicking on the website

and then click on 'Add new' item; select the web service option, give a suitable

name and click on Add.

In Solution Explorer window, open the Service.asmx file. In the code that shows up, change the class name to 'pcquest.webservice.service'

Once the new service has been added, find the line:

“To allow this Web Service to be called from script, using ASP.NET AJAX,

uncomment the following line:”

'

ScriptService()>

You need additional attributes to use this web service, so 'uncomment' the

above line. Now we shall explicitly mention the namespace and keep every single

code inside this namespace. An example of the code is shown below:

Imports System.Web



Imports System.Web.Services


Imports System.Web.Services.Protocols


Namespace pcquest.webservice


'all the code inside this section


End Namespace

After this double click on the 'service.asmx' file and replace the class name

service with the name of the namespace i.e. pcquest.webservice. The line in

service.asmx file should like this:

“<%@ WebService Language="vb" CodeBehind="~/App_Code/Service.vb"

Class="pcquest.webservice" %>”

Once this is done, right click on the service.asmx file and view it on

Internet Explorer. It should show the web service page; click on the invoke

button on the web page to test the web service.

Now it's time for client side coding. For this close the current Web

Developer 2008 project and start a fresh project. This time we will be creating

a new ASP.NET AJAX website. Provide a suitable name and click on Ok. As the page

appears we see a couple of standard code already written.

We shall modify those codes according to our needs. First give a title to

your web page, for eg, 'Website for testing web services' and then delete

everything that is inside the 'Body' tag. Place the following code inside the

body:

Open the service.asmx file of the server in the browser and copy the URL in the source code of the client's website for accessing the web service

And in the 'head' tag place these two functions:

And that's all, save your project and view your client web page on the web

browser. Now click on the button which is on the web page and you will get an

alert which says 'Hello'. Similarly you can use this to retrieve the status of

some process or project.



Web services can also be used to retrieve any data from the database and deliver
the required data to the client side.