How do i call WCF services in Silverlight?

Tuesday, August 24, 2010 by Nate Bross

Someone asked on Stack Overflow:

Can anybody tell me why is this not working. I have created a WCF service which returns a list of customers from Northwind database.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Runtime.Serialization;
using System.ServiceModel;
using System.Text;
using System.ServiceModel.Activation;

namespace WCFSilverlight.Web
{
    // NOTE: You can use the "Rename" command on the "Refactor" menu to change the class name "Customers" in code, svc and config file together.
    [AspNetCompatibilityRequirements(RequirementsMode = AspNetCompatibilityRequirementsMode.Allowed)]

    public class Customers : ICustomers
    {

        IEnumerable<Customer> ICustomers.GetAllCustomers()
        {
            NorthwindEntities objNorthwindEntities = new NorthwindEntities();
            var query = from cust in objNorthwindEntities.Customers
                        select cust;
            return query.ToList();
        }
    }
}

And this is my App.xaml.cs code fragment :-

private void Application_Startup(object sender, StartupEventArgs e)
{
    this.RootVisual = new MainPage();
    CustomersClient objCustomersClient = new CustomersClient();
    objCustomersClient.GetAllCustomersCompleted += new EventHandler<GetAllCustomersCompletedEventArgs>(client_GetNameCompleted);
    objCustomersClient.GetAllCustomersAsync();
}

void client_GetNameCompleted(object sender, GetAllCustomersCompletedEventArgs e)
{
    MessageBox.Show(e.Result.ToString());      
}

If I am not wrong the methods in Silverlight are called asynchronously. So I have added a event handler to handle it and then called the method to retrieve customers. But I don’t get anything in Messagebox. Further when I try to keep a breakpoint on client_GetNameCompleted, it never executes. But if I keep it in Application_Startup it does execute. What can be the problem?

Also explain me am I doing it correct? I’ve seen one example where one person directly defines the function using some strange symbols like =>.

EDIT 1:- Kindly also explain me what is e.UserState in e. What does it contain and what can I possibly do with it?

EDIT 2 :- :- I get this error http://img178.imageshack.us/img178/9070/53923202.jpg

The WCF service is working perfectly i have tested the link query. So there is no problem with Sql Server connection or WCF. Something is wrong with my client only.

This is my ServiceReference.ClientConfig :-

<configuration>
    <system.serviceModel>
        <bindings>
            <basicHttpBinding>
                <binding name="BasicHttpBinding_ICustomers" maxBufferSize="2147483647"
                    maxReceivedMessageSize="2147483647">
                    <security mode="None" />
                </binding>
            </basicHttpBinding>
        </bindings>
        <client>
            <endpoint address="http://localhost:50622/Customers.svc" binding="basicHttpBinding"
                bindingConfiguration="BasicHttpBinding_ICustomers" contract="CustomerServ.ICustomers"
                name="BasicHttpBinding_ICustomers" />
        </client>
    </system.serviceModel>
</configuration>

Can you now tell me what is wrong?

Thanks in advance :)

Update :- I read in google you need to set serialization mode to unidirectional. But where do i set this? What do i write where?

I posted the following answer, which was chosen as the accepted answer and received 2 upvotes:

1. You are correct, All network calls in Silverlight are done asynchronously.
2. The => syntax you mention is shorthand for defining a delegate method, its called a lambda. (see below)
3. You should be able to set a break-point in the Completed event handler, if not try restarting Visual Studio (I’ve seen it act strangly before).
4. e.UserState will have a reference to whatever object you put in the UserState variable for the async call (note the extra overload).

Code:

objCustomersClient.GetAllCustomersCompleted = delegate(object Sender, GetAllCustomersCompletedEventArgs e) 
{
    MessageBox.Show(e.Result.ToString());        
}; 

// is the same as

objCustomersClient.GetAllCustomersCompleted += new EventHandler<GetAllCustomersCompletedEventArgs>(client_GetNameCompleted); 
void client_GetNameCompleted(object sender, GetAllCustomersCompletedEventArgs e) 
{ 
    MessageBox.Show(e.Result.ToString());       
} 

// which is same as

objCustomersClient.GetAllCustomersCompleted += (sender, e) => { MessageBox.Show(e.Result.ToString());  }; 

Originally posted on Stack Overflow — 2 upvotes (accepted answer). Licensed under CC BY-SA.