A Beginner's Tutorial for Understanding Windows Communication Foundation (WCF)

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Introduction

This article is an introduction to the Windows Communication Foundation (WCF). We will try to see the basic concepts behind WCF and will try to implement a small WCF service. We will also work out some small examples of how a WCF service can be consumed.

Background

Like I said in my earlier article on Web Services, communication between applications is very important. Web services provide an efficient way of facilitating communication between applications. But there are limitations with web services too. The major limitation with web services is that the communication can happen over HTTP only. A second limitation with web services is that it provides simplex communication and there is no way to have half duplex or full duplex communication using web services. 

Windows Communication Foundation (WCF) comes to the rescue when we find ourselves not able to achieve what we want to achieve using web services, i.e., other protocols support and even duplex communication. With WCF, we can define our service once and then configure it in such a way that it can be used via HTTP, TCP, IPC, and even Message Queues. We can consume Web Services using server side scripts (ASP.NET), JavaScript Object Notations (JSON), and even REST (Representational State Transfer).

The following table illustrates the differences between a web service and a WCF service:

Note: Apart from these differences, there are other differences related to instance management, sessions, and data representation and serialization. We will not discuss these here as they tend to be digressing for beginners.

A WCF service can be visualized as:

Understanding the basics

When we say that a WCF service can be used to communicate using different protocols and from different kinds of applications, we will need to understand how we can achieve this. If we want to use a WCF service from an application, then we have three major questions:

1. Where is the WCF service located from a client's perspective?
2. How can a client access the service, i.e., protocols and message formats?
3. What is the functionality that a service is providing to the clients?

Once we have the answer to these three questions, then creating and consuming the WCF service will be a lot easier for us. The WCF service has the concept of endpoints. A WCF service provides endpoints which client applications can use to communicate with the WCF service. The answer to these above questions is what is known as the ABC of WCF services and in fact are the main components of a WCF service. So let's tackle each question one by one.

Address: Like a webservice, a WCF service also provides a URI which can be used by clients to get to the WCF service. This URI is called as the Address of the WCF service. This will solve the first problem of "where to locate the WCF service?" for us.

Binding: Once we are able to locate the WCF service, we should think about how to communicate with the service (protocol wise). The binding is what defines how the WCF service handles the communication. It could also define other communication parameters like message encoding, etc. This will solve the second problem of "how to communicate with the WCF service?" for us.

Contract: Now the only question we are left up with is about the functionalities that a WCF service provides. Contract is what defines the public data and interfaces that WCF service provides to the clients.

Using the code

As an ASP.NET developer, we will find ourselves in the need of using a WCF service or perhaps write a WCF service. What we will do next is to implement a small WCF service and see how the ABC of WCF is to be implemented. We will then write a small application to consume this WCF service.

The service that we will create will provide arithmetic operations on a Pair data type. This Pair type will also be exposed by our service to the applications. We will simply provide addition and subtraction functionality for the Pair data type.

Note: We will host this WCF service inside an ASP.NET website, i.e., IIS hosting, and will be consuming it from an ASP.NET website. So let us create an empty ASP.NET website and then add a WCF service to it.

Creating a WCF Service

Let us start by looking at the Contract part of the WCF service. We need to expose a Pair data type from our service so this class will have to be decorated with the DataContract attribute. This attribute specifies that this data type can be used by consumers of this WCF service. Also, the public properties of this class will have to be decorated with the DataMember attribute to specify that clients can use these properties and to indicate that they will be needing serialization and deserialization.

[DataContract]
public class Pair
{
    int m_first;
    int m_second;

    public Pair()
    {
        m_first = 0;
        m_second = 0;
    }

    public Pair(int first, int second)
    {
        m_first = first;
        m_second = second;
    }

    [DataMember]
    public int First
    {
        get { return m_first; }
        set { m_first = value; }
    }

    [DataMember]
    public int Second
    {
        get { return m_second; }
        set { m_second = value; }
    }
}

Now we have specified the Data contract that our service is exposing. The next thing is to specify the service contracts and major operations of this service. Let us create an interface that will list the major functionalities provided by this service. We will then have to decorate this interface with the ServiceContract attribute to specify that this interface is being exposed by this service and can be used by the clients.

We will then have to write methods for all major operations provided by this service and decorate them with the OperationContract attribute to specify that these operations of this interface can be used by the clients.

public interface IPairArihmeticService
{
    [OperationContract]
    Pair Add(Pair p1, Pair p2);

    [OperationContract]
    Pair Subtract(Pair p1, Pair p2);
}

Now we have specified all the DataContract, ServiceContract, and the OperationContract of our small service. Now the major thing left in this service is to implement the functionalities. To do that, let's have a small class that will implement the interface we just created.

public class PairArihmeticService : IPairArihmeticService
{
    Pair IPairArihmeticService.Add(Pair p1, Pair p2)
    {
        Pair result = new Pair();

        result.First = p1.First + p2.First;
        result.Second = p1.Second + p2.Second;

        return result;
    }

    Pair IPairArihmeticService.Subtract(Pair p1, Pair p2)
    {
        Pair result = new Pair();

        result.First = p1.First - p2.First;
        result.Second = p1.Second - p2.Second;

        return result;
    }
}

Let us try to visualize what we have done so far. This class diagram will show the classes we created so far and decorated them with attributes to specify the data contract, service contract, and operation contracts.

We have our Contract part declared and defined. Now let us see how we can configure the other things. We need to make this service visible to the client applications and let the client applications extract the meta data information out of this service. To do this we need to specify the service behavior in the web.config.

<system.serviceModel>
    <behaviors>
      <serviceBehaviors>
        <behavior name="">
          <serviceMetadata httpGetEnabled="true"/>
          <serviceDebug includeExceptionDetailInFaults="false"/>
        </behavior>
      </serviceBehaviors>
    </behaviors>
    <serviceHostingEnvironment multipleSiteBindingsEnabled="true"/>
</system.serviceModel>

The important thing to notice here is the httpGetEnabled="true" which enables this service to provide its meta data when a client requests for it. Now let us build this website to build our WCF service. Let us set the .SVC file as the start page and run the website to see what happens.

Consuming a WCF Service

We have seen how to create a WCF service. Let us now see how we can consume a WCF service. Let us start by adding a default ASP.NET website in the same solution. We then need to add a service reference to the WCF service we just created.

Adding this service reference will mainly do two things:

1. Create the Address and Binding part to access this service in the web.config file.
2. Create the proxy class for us to access the service.

So let us first look at the Address and Binding in the web.config to complete the ABC part of the WCF service.

<system.serviceModel>
    <bindings>
      <basicHttpBinding>
        <binding name="BasicHttpBinding_IPairArihmeticService"/>
      </basicHttpBinding>
    </bindings>
    <client>
      <endpoint address="http://localhost:1062/WcfTestWebSite/PairArihmeticService.svc" 
          binding="basicHttpBinding" bindingConfiguration="BasicHttpBinding_IPairArihmeticService" 
          contract="PairServiceReference.IPairArihmeticService" 
          name="BasicHttpBinding_IPairArihmeticService"/>
    </client>
</system.serviceModel>

This web.config shows the address of the WCF service, the binding to use the webservice, and the contract that is being exposed by this web service. All this was generated by extracting the meta data from the service.

Now let us look at how to use the proxy class that was generated. We will use this proxy class to call the methods of the WCF service and then extract the results out of it.

PairServiceReference.Pair p1 = new PairServiceReference.Pair();
p1.First = Convert.ToInt32(txtP1First.Text);
p1.Second = Convert.ToInt32(txtp1Second.Text);

PairServiceReference.Pair p2 = new PairServiceReference.Pair();
p2.First = Convert.ToInt32(txtP2First.Text);
p2.Second = Convert.ToInt32(txtp2Second.Text);

PairServiceReference.PairArihmeticServiceClient pairServiceClient = 
           new PairServiceReference.PairArihmeticServiceClient();
PairServiceReference.Pair addResult = pairServiceClient.Add(p1, p2);

PairServiceReference.Pair minusResult = pairServiceClient.Subtract(p1, p2);

lblsum.Text = addResult.First.ToString() + ", " + addResult.Second.ToString();
lblminus.Text = minusResult.First.ToString() + ", " + minusResult.Second.ToString();

Note: The above code snippet refers to control IDs. Please see the source code for that.

Now we have successfully consumed the WCF service from our ASP.NET website. Before we wrap up, let us now build this web site and see the results.

Note: While using the source code, the service reference will have to be updated to added again as the address of the service that was being used was specific to my system. It could differ on other systems.

Points of interest

What we have tried to do here is to understand some basic concepts of a WCF service. We created a sample WCF service. We have also created a sample website to consume the WCF service.

There are various alternatives when it comes to hosting, accessing, and using a WCF service. We have only looked at one particular way. One good exercise would be to change this service to make it accessible via AJAX. It is more like a WCF service involves some code and some configuration. If we need to use different sets of ABCs for this service, then the code (logic) will not change, the only change that will be required is in the configurations.

History

• 18 June 2012: First version.