Accessing web services using Silverlight

BANGALORE, INDIA: There area number of ways that a Silverlight client can access external data like a typical scenario, where data is in a relational database with Silverlight interface to it. Another interesting scenario is consumption of data as a web service by a Silverlight client.

Again there are two different ways in which one can access web services. In this implementation, we are describing how to access web services via proxy generated from metadata published by the service. One can also access these services directly.

using System.ServiceModel;
using System.ServiceModel.Activation;

namespace SilverlightApplication4.Web
{


public class PcquestService
{

public int CountUsers()
{
return 2;
}

public User GetUser(int id)
{
if (id == 1)
{
return new User() { IsMember = true, Name = "Sandeep", Age = 95 };
}
else
{
return new User() { IsMember = false, Name = "Sandy", Age = 55 };
}
}
}

One important point here is to use valid type and the simplest way to achieve this is to make types public with public members and public constructures.

public class User
{

public bool IsMember { get; set; }

public string Name { get; set; }

public int Age { get; set; }
}
}

To test if this service is working properly simply right click on 'PcquestService.svc' file in solution explorer and click on 'View in Browser'. This will display test page for the service. Now as we have service, we need to access it. We will start with adding service reference to service. In the same project, right click on 'SilverlightApplication4' in solution explorer and select 'Add Service Reference'.

In pop up window, click on 'Discover' button, this will show 'PcquestService.svc' service we have just created. Accept 'ServiceReference1' in the 'Namespace' field and click on 'OK'. Next step is to create proxy to the service. Go to 'Page.xaml.cs' and add followimg reference:

using System.ServiceModel;
using SilverlightApplication4.ServiceReference1;

Before one can use service, web service proxy needs to be initated. Here this is done inside 'OnClick()'. Web service calls in Silverlight are asynchronous. The proxy contain two members for each operation in the service; an asynchronous method and completed event. For example, in our implementation in 'CountUser' service operation, we first add 'EventHandler' to 'CountUserCompleted' event.

This event would be invoked when service returns data. After event is setup, we can make call to service by calling 'CountUserAsyn()'. The event handler specifies that 'proxy_CountUser Completed()' is called when the service returns some data.

namespace SilverlightApplication4
{
public partial class Page : UserControl
{
public Page()
{
InitializeComponent();
}
void OnClick(object sender, EventArgs args)
{
PcquestServiceClient proxy = new PcquestServiceClient();
proxy.CountUsersCompleted += new EventHandler(proxy_CountUsersCompleted);
proxy.CountUsersAsync();
proxy.GetUserCompleted += new EventHandler(proxy_GetUserCompleted);
proxy.GetUserAsync(1);
}
void proxy_GetUserCompleted(object sender, GetUserCompletedEventArgs e)
{
getUserResult.Text = "User name: " + e.Result.Name + ", age: " + e.Result.Age + ", is member: " + e.Result.IsMember;
}
void proxy_CountUsersCompleted(object sender, CountUsersCompletedEventArgs e)
{
if (e.Error == null)
{
userCountResult.Text = "Number of users: " + e.Result;
}
else
{
userCountResult.Text = "Error getting the number of users";
}
}
}
}

Here we are showing the content of 'Page.xaml' file. This is done to display results. Here results are shown in 'TextBlock':

xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Width="400" Height="300">











All in all, this shows how easy it is to access web services using Silverlight client. This can help web developers to add more data to their silverlight based web sites.