Writing Your First Web Service
The main file that we will work with in this project is the Service1.asmx file. This file (actually the code behind this file) contains the functions that your web service will expose. Open the code behind the Service1.asmx page by right mouse clicking on the file name (from the Solution Explorer window) and choosing "View Code." You will notice that Visual Studio has already added nearly 50 lines of code. Since we want to develop a simple math library, we're going to remove all the code that was generated in the Service1.asmx "code behind" file and replace it with just a few lines of code that provide us with the math functionality we intend to create:

Imports System.Web.Services
Public Class Service1
Inherits System.Web.Services.WebService

Public Function <WebMethod()> Add(ByVal n1 As
Integer, _ ByVal n2 As Integer) As Integer
Return n1 + n2
End Function

Public Function <WebMethod()> Multiply(ByVal n1 As
Integer, _ ByVal n2 As Integer) As Integer
Return n1 * n2
End Function
End Class

Let's go through this code, in small chunks that we can easily understand. The first line,

Imports System.Web.Services
allows us to use a certain set of functionality provided by the .NET Framework that pertains to web services. This is a set of libraries that Microsoft has already developed for developers to use.

Next, we see:

Public Class Service1
Inherits System.Web.Services.WebService
These two lines of code create a new class, called "Service1", which inherits some the web service functionality from the "WebService" class that Microsoft has developed and made available through the System.Web.Services library. We imported that library in the first line of code.

Next, we have our first web method (or function in this case):

Public Function <WebMethod()> Add(ByVal n1 As Integer, _
ByVal n2 As Integer) As Integer
Return n1 + n2
End Function

Notice that this function looks exactly like a normal Visual Basic function, with the one exception that it has a <WebMethod()> prefix before the function name. The WebMethod() prefix tells the compiler to make this function available as a function that can be called through the web. The contents of the function could be anything you develop. You can access a database and send the number of records. You can write a function that even returns the records of a table in a database. There are no limits. Practically anything that can be done in a normal function can be done in a web function that's invoked over the web.

That's all there is to it. We have now created our web service with two functions exposed as web methods. Lets use them!

Notice that this function looks exactly like a normal Visual Basic function, with the one exception that it has a <WebMethod()> prefix before the function name. The WebMethod() prefix tells the compiler to make this function available as a function that can be called through the web. The contents of the function could be anything you develop. You can access a database and send the number of records. You can write a function that even returns the records of a table in a database. There are no limits. Practically anything that can be done in a normal function can be done in a web function that's invoked over the web.

That's all there is to it. We have now created our web service with two functions exposed as web methods. Lets use them!