Enumerate the Steps for creating a Shared Assembly

Step 1: Generate a Strong Name Key:

D:\Project\DLL\sn -k dll.snk

The above statement will write a Kay pair to dll.snk file

Step 2: Associate the Strong Name Key with source code

Step 2.1: Create a program to be used as DLL - First.cs

using System;
using System.Reflection;

[assembly:AssemblyKeyFile("dll.snk")]
public class Employee
{
public string Data()
{
return "Anuj Ranjan";
}
}

a) Save the file as First.cs in D:\Project\DLL\First.cs
b) Compile the program to create a DLL from the Command Prompt as given below:

D:\Project\DLL>csc /t:library First.cs

c) The above statement will create a DLL named First.dll, with the strong name key in it.

Step 2.2: Create another program to implement the DLL - Second.cs

using System;

public class Trial
{
public static void Main()
{
Employee e = new Employee();
Console.WriteLine(e.Data());
}
}

Save the file as Second.cs in D:\Project\Implement\Second.cs

Step 3: Install the DLL in GAC

D:\Project\DLL\GACUTIL -i First.dll

GACUTIL is a command which is used to install a strong named dll in the Global Assembly Cache.

Step 4: Add the reference of the DLL in the program

D:\Project\Implement\csc /r:d:\Project\DLL\First.dll Second.cs

Step 5: Execute the program

D:\Project\Implement\Second

Fundamental Windows Communication Foundation Concepts

WCF programming model consists of a runtime and a set of APIs and is used for creating systems that communicate (sends and receives messages) between clients and services.

Messaging and Endpoints

The main concept of WCF is Message–Based Communication. In the programming model anything that can can be modeled as a message (an HTTP request, a Message Queuing – MSMQ, etc), can be represented in a uniform way. This concept enables a unified API across contrasting transport mechanisms.

A client is an application which initiates a communication, while a service is an application which responds to the client's request. However, the client and the service may not be necessarily different applications, a single application may in fact act both as a client and a service (Duplex Services and Peer–to– Peer Networking).

As Endpoints are points or spots for message exchange, they define all the information required to facilitate message exchange. A WCF service can expose single or multiple endpoints (application endpoints or infrastructure endpoints or both). The client generated endpoint should be compatible with one of the service's endpoints.

Endpoints describe the address (location of the endpoint where the messages should be send), binding (how a client can communicate with the endpoint by sending messages), contracts (form of the message) and behaviors (local implementation details of the endpoint). This information can be exposed by the service as metadata, that can be processed to generate appropriate WCF clients and communication stacks.

Communication Protocols

The two elements required in the communication stack is given below:

• Transport protocol – Messages can be exchanged over the internet using common protocols such as HTTP and TCP. Protocols that support communication with Message Queuing applications and nodes on a Peer Networking mesh are also included.
• Encoding mechanisms – Encoding mechanisms specify the format of a message. Following encoding mechanisms are provided by WCF:
  a) Text encoding – this is an interoperable encoding.
  b) Message Transmission Optimization Mechanism (MTOM) encoding – this is an interoperable way for efficiently sending unstructured binary data to and from a service.
  c) Binary encoding – this is implemented for efficient transfer.

Note: Even more encoding mechanisms (for example, a compression encoding) can be added using the built-in extension points of WCF.

Message Patterns

Amongst the several messaging patterns supported by WCF, the most common Message Exchange Patterns include Request–Reply, One–Way, and Duplex. The variety of interactions supported by different protocols depends on the fact that they support different Message Exchange Patterns (MEX).

The messages exchanged in WCF is secure and reliable (a feature of WCF APIs and runtime).

Conversion of Seconds to Hours:Minutes:Seconds format

Recently I faced a requirement of converting seconds to Hours:Minutes:Seconds format. After some R&D, I found the following solution:

CODE

DECLARE @in_seconds int

SET @in_seconds = 3661 -- One Hour One Minute and One Second

SELECT CONVERT(CHAR(8), DATEADD(SECOND, @in_seconds, 0), 108) As Hour_Minute_Second

OUTPUT

01:01:01

Note: This SQL code is applicable only for time less than 24 hours.

Message Patterns in WCF Services

Client applications and WCF services communicate by passing XML messages. Message Exchange Patterns illustrate how clients and services communicate by passing messages. There are three message exchange patterns supported by WCF:

·         Request – Reply Message Exchange Pattern

·         One – Way Message Exchange Pattern (also called Datagram)

·         Duplex Message Exchange Pattern (also called Callback)

Request – Reply Message Exchange Pattern

After sending message to a WCF service, a client application waits for the reply in Request – Reply pattern. This is the default and classic pattern for both WCF and Web Services. Since the client has asked a question, and it expects an answer, it waits for the service to send a message back containing the answer.

The Request – Reply message exchange pattern is used when a client requests a service to perform an action, and it needs some confirmation. Fault exception is handled in Request – Reply pattern. The Request – Reply pattern is the most used message exchange pattern.

In Request – Reply Message Exchange Pattern, only the client can initiate a communication with the service.

One – Way Message Exchange Pattern

The One – Way Message Exchange Pattern is also known as Datagram or Fire and Forget. This pattern is used when a client requests the service to take an action but it does not need any confirmation. Thus neither the service sends a reply message not the client waits for a reply. A client sends a message (request) to a WCF service but the service does not send a reply message to the client. The client does not wait for the reply and proceeds with other processing work. Some scenario’s for one-way pattern includes logging in and out, maintenance tasks, heads down data entry and other repetitive tasks etc.

An implication of using one – way pattern is that even if a method call fails due to an exception or invalid data, the service does not notify the client. If the client needs to be notified about the failure of the service request, then this pattern should not be used. This pattern should be used when the client does not need to wait for a reply from the WCF service.

In One – Way Message Exchange Pattern, only the client can initiate a communication with the service.

Duplex Message Exchange Pattern

The Duplex Message Exchange Pattern is also known as Callback. Both the client and the service can initiate a communication in the duplex pattern. It can be used for transactions. The client calls the service, which after processing the request, callbacks the client with the reply. In the meanwhile, instead for waiting for the reply (as in Request – Reply pattern), the client proceeds with other tasks.

This pattern should be used when the client (after the client has called the service) expects a notification or alert from the WCF service.

Note: The One – Way and Duplex patterns provides opportunities to fine-tune the performance of applications and to add more flexibility regarding what happens after a client calls a service.

The presence of One – Way and Duplex patterns in WCF is a major advantage of WCF over Web Services.

Polymorphism in C#

Polymorphism is the ability of an object oriented language (C# in this context) to allow a base class to define a set of members (formally termed the polymorphic interface) that are available to all descendents. A class’s polymorphic interface is constructed using any number of virtual or abstract members.

A virtual member is a member in a base class that defines a default implementation that may be changed (overridden) by a derived class.

In contrast, an abstract method is a member in a base class that does not provide a default implementation, but does provide a signature. When a class derives from a base class defining an abstract method, it must be overridden by a derived type.

In either case (virtual or abstract), when derived types override the members defined by a base class, they are essentially redefining how they respond to the same request.

Method Overriding – Method Overriding is a process in which a derived class can define its own version of a method, which was originally defined by its base class.

Virtual Keyword – The virtual keyword indicates that the base class wants to define a method which may be (but does not have to be) overridden by a derived class. A virtual method provides a default implementation that all derived types automatically inherit. If a child class so chooses, it may override the method but does not have to.

Note: Subclasses are never required to override virtual methods.

Override Keyword – The override keyword is used by a derived class to to change the implementation details of a virtual method (defined in the base class). Each overridden method is free to leverage the default behavior of the parent class using the base keyword.

Sealed Keyword – The sealed keyword is basically applied to classes to prevent other types from extending its behavior via inheritance.

It can also be applied to virtual methods to prevent derived types from overriding those methods. Ex.

public override sealed void GiveBonus(float amount)

{

...

}

Any effort to override the above sealed method in the derived class will generate compile time error.

Abstract Classes – The abstract keyword can be used in the class definition to prevent direct creation of an instance of the class. Although abstract classes cannot be created directly, it is still assembled in memory when derived classes are created. Thus, it is perfectly fine for abstract classes to define any number of constructors that are called indirectly when derived classes are allocated.

An abstract class can define any number of abstract members (members that does not supply a default implementation, but must be accounted for by each derived class).

The polymorphic interface of an abstract base class simply refers to its set of virtual and abstract methods. Methods marked with abstract are pure protocol. They simply define the name, return type (if any), and parameter set (if required).

If you do not override an abstract method (of the base abstract class) in the derived class, the derived class will also be considered abstract, and would have to be marked abstract with the abstract keyword.

Although it is not possible to directly create an instance of an abstract base class, you can freely store references to any subclass with an abstract base variable.

Q: What is an efficient way to force each child class to override a virtual method?

A: To force each child class to override a virtual method, we can better define an abstract method (which by definition means you provide no default implementation whatsoever), in an abstract class.

Inheritance in C#

Inheritance is the ability of an object oriented language (C# in this context) to build new class definitions based on existing class definitions. Inheritance allows us to extend the behavior of a base (parent) class by inheriting core functionality into the derived subclass (child class). Inheritance promotes code re-usability.

Inheritance preserves encapsulation – private members of the base class can never be accessed from an object reference of the derived class. Private members can only be accessed by the class that defines it.

C# does not support Multiple Inheritance. A class in C# cannot directly derive from two or more base classes.