Web Services

Using the Currency Web Service

The Currency Web Service developed by us has the following features:

1. It can return a list of all countries in the world
2. It can return a list of currency symbols and names for respective countries. Note that each currency in the world has a three letter symbol, e.g. INR, JPY, USD, EUR etc.
3. It can return a rate of conversion from any currency to any other currency. This is a live rate which is updated in real time.

Let us now use these features of the Currency Web Service in our application. To do this, we will create a WinForm application using C#. We will assume that you have at least a nodding acquaintance with the creation of a WinForm application in VS2005. Our application will be able to get currency conversion rates in bulk, even though the web service can only get one rate of conversion at a time.

Given below are the steps involved in building the WinForm application:

(a) Create a new Visual C# WinForm (Windows Application) project called CurrencyClient01.

(b) Drag and drop controls on the WinForm as shown in Figure 4. Give names to the controls as indicated in the figure.

Figure 4 – WinForm Controls

(c) Add Web Reference to the CurrenyWebService from Solution explorer window by right clicking on References node. When prompted to enter the reference name, add com.ksetindia.ws.currency as shown in Figure 5.

Figure 5 – Add Web Reference to CurrencyWebService

Visual Studio creates a proxy class called CurrencyWebService on your machine. It communicates with the web service. The class is automatically placed inside the namespace CurrencyClient01.com.ksetindia.ws.currency. We have to add the following statement at the top of CurrencyClient.cs to be able to use the proxy class:

using CurrencyClient01.com.ksetindia.ws.currency;

(d) Add event handlers CurrencyClient_Load( ) and GoButton_Click( ) to CurrencyClient.cs.

Before we get into the event handlers, we need to do some initialization work in the constructor. This is shown below:

private CurrencyService                                            service ;
private SortedDictionary<String, CountryCurrency> countries ;

public CurrencyClient( )
{
  InitializeComponent( ) ;
  service = new CurrencyService( ) ;
  countries = new SortedDictionary<string, CountryCurrency>( ) ;
  foreach( CountryCurrency c in service.GetCountryCurrencies( ) )
    countries.Add ( c.country, c ) ;
}

To use the web service, we must create an object of the proxy class CurrencyService. Following this, we have obtained the list of counties and their currencies by calling the web service function GetCountryCurrencies( ) using the object service. For easy lookup from country name to its currency and symbol, we have created a sorted dictionary with county name as the key and CountryCurrency object as the value. Each CountryCurrency object holds country name, currency and its symbol.