WCF interview questions and answers

WCF, all services expose contracts. The contract is a platform-neutral and standard way of describing what the service does. 

WCF defines four types of contracts. 


Service contracts 

Describe which operations the client can perform on the service. 
There are two types of Service Contracts. 
ServiceContract - This attribute is used to define the Interface. 
OperationContract - This attribute is used to define the method inside Interface. 

[ServiceContract]

interface IMyContract

{

   [OperationContract]

   string MyMethod( );

}

class MyService : IMyContract

{

   public string MyMethod( )

   {

      return "Hello World";

   }

}

Data contracts 

Define which data types are passed to and from the service. WCF defines implicit contracts for built-in types such as int and string, but we can easily define explicit opt-in data contracts for custom types. 

There are two types of Data Contracts. 
DataContract - attribute used to define the class 
DataMember - attribute used to define the properties. 

[DataContract]

class Contact

{

   [DataMember]

   public string FirstName;

   [DataMember]

   public string LastName;

}

If DataMember attributes are not specified for a properties in the class, that property can't be passed to-from web service. 

Fault contracts 

Define which errors are raised by the service, and how the service handles and propagates errors to its clients. 


Message contracts 

Allow the service to interact directly with messages. Message contracts can be typed or untyped, and are useful in interoperability cases and when there is an existing message format we have to comply with.

Q1. What is WCF?

WCF stands for Windows Communication Foundation. It is a Software development kit for developing services on Windows. WCF is introduced in .NET 3.0. in the System.ServiceModel namespace. WCF is based on basic concepts of Service oriented architecture (SOA)

Q2. What is endpoint in WCF service?

The endpoint is an Interface which defines how a client will communicate with the service. It consists of three main points: Address,Binding and Contract.

Q3. Explain Address,Binding and contract for a WCF Service?

Address:Address defines where the service resides.
Binding:Binding defines how to communicate with the service.
Contract:Contract defines what can be done with the service.

Q4. What are the various address format in WCF?

a)HTTP Address Format:--> http://localhost:
b)TCP Address Format:--> net.tcp://localhost:
c)MSMQ(MicroSoft Message Queue) Address Format:--> net.msmq://localhost:

Q5. What are the types of binding available in WCF?

A binding is identified by the transport it supports and the encoding it uses. Transport may be HTTP,TCP etc and encoding may be text,binary etc. The popular types of binding may be as below:
a)BasicHttpBinding
b)NetTcpBinding
c)WSHttpBinding
d)NetMsmqBinding

Q6. What are the types of contract available in WCF?

The main contracts are:
a)Service Contract:Describes what operations the client can perform.
b)Operation Contract : defines the method inside Interface of Service.
c)Data Contract:Defines what data types are passed
d)Message Contract:Defines wheather a service can interact directly with messages

Q7. What are the various ways of hosting a WCF Service?

a)IIS b)Self Hosting c)WAS (Windows Activation Service)

Q8. What is the proxy for WCF Service?

A proxy is a class by which a service client can Interact with the service.
By the use of proxy in the client application we are able to call the different methods exposed by the service

Q9. How can we create Proxy for the WCF Service?

We can create proxy using the tool svcutil.exe after creating the service.
We can use the following command at command line.
svcutil.exe *.wsdl *.xsd /language:C# /out:SampleProxy.cs /config:app.config

Q10.What is the difference between WCF Service and Web Service?

a)WCF Service supports both http and tcp protocol while webservice supports only http protocol.
b)WCF Service is more flexible than web service.

Address (Where):- An address indicates where we can find this service. Address is a URL, which points to the location of the service.

Bindings (How):- Bindings determined that how this end can be accessed. It determines how communication is done. For instance, you expose your service, which can be accessed using SOAP over HTTP or BINARY over TCP. So for each of these communications medium two bindings will be created.

Contracts (What):- Contract is an agreement between two or more parties. It defines the protocol how client should communicate with your service. Technically, it describes parameters and return values for a method.