Memento Design Pattern in C#

The Memento Design Pattern is a Behavioral Design Pattern that can restore an object to its previous state. This pattern is useful for scenarios where you need to perform an undo or rollback operation in your application. The Memento pattern captures an object’s internal state so that the object can be restored to this state later. It is especially useful when implementing undo functionality in an application.

Component of Memento Design Pattern

1. Originator: The object whose state you want to save or restore.
2. Memento: Stores the internal state of the Originator. It has two interfaces:
   • Caretaker Interface: This interface provides no access to the internal state of the Memento. It is used by the Caretaker to manage the Memento without modifying it.
   • Originator Interface: This interface allows the Originator to access the Memento to restore its state.
3. Caretaker: The object that requests the saving and restoring of the Originator’s state.

Iterator Design Pattern in C#

The Iterator Design Pattern is a behavioral design pattern that allows sequential access to the elements of an aggregate object (i.e., collection) without exposing its underlying representation. That means using the Iterator Design Pattern, we can access the elements of a collection sequentially without knowing its internal representations. This pattern provides a uniform interface for traversing different data structures.

The collections in C#, like List, ArrayList, Array, etc., are containers containing many objects. In object-oriented programming, the iterator pattern is a design pattern in which an iterator is used to traverse a container and access the elements of the container.

Components of Iterator Pattern

• Iterator: The interface that defines the methods for traversing the collection.
• Concrete Iterator: The class that implements the iterator interface and performs the actual traversal.

Interpreter Design Pattern in C#

The Interpreter Design Pattern is a behavioral design pattern that defines a grammatical representation for a language and provides an interpreter to deal with this grammar. This pattern is particularly useful for designing simple languages or interpreting expressions.

When to Use the Interpreter Pattern

• When you have a simple language to interpret.
• When you need to interpret expressions in a language.
• When the grammar of the language is relatively simple and stable.

Visitor Design Pattern in C#

The Visitor Pattern is a behavioral design pattern that allows you to add further operations to objects without having to modify them. It is particularly useful when you have a structure of objects and you want to perform operations on these objects that can be defined outside of their classes. This pattern follows the Open/Closed Principle by allowing new functionality to be added without altering the existing code.

The Visitor Design Pattern should be used when you have distinct and unrelated operations to perform across a structure of objects (element objects). That means the Visitor Design is used to create and perform new operations on a set of objects without changing the object structure or classes.

Components of Visitor Pattern

1. Visitor Interface: Declares a Visit method for each type of ConcreteElement in the object structure.
2. ConcreteVisitor: Implements the Visitor interface and defines the actions for each type of ConcreteElement.
3. Element Interface: Declares an Accept method that takes a Visitor as an argument.
4. ConcreteElement: Implements the Element interface and defines the Accept method to call the Visitor's method.
5. Object Structure: Can be a collection or a composite of elements which can be iterated to apply the Visitor.

State Design Pattern in C#

The State Design Pattern is a behavioral design pattern that allows an object to alter its behavior when its internal state changes. This pattern is particularly useful for implementing state machines and ensuring that the object’s behavior remains manageable and modular.

This pattern is useful when an object needs to go through several states, and its behavior differs for each state. Instead of having conditional statements throughout a class to handle state-specific behaviors, the State Design Pattern delegates this responsibility to individual state classes.

Components of State Desgin Pattern

1. Context: This is the class that contains an instance of a state and delegates state-specific behavior to the current state object.
2. State: An interface that encapsulates the behavior associated with a particular state of the Context.
3. Concrete States: Classes that implement the State interface, each representing a specific state and defining its behavior.

Chain of Responsibility Pattern in C#

The Chain of Responsibility pattern is a behavioral design pattern that allows a group of objects to handle a request sequentially, each potentially handling the request or passing it on to the next object in the chain until the request is handled or reaches the end of the chain.

In simple words, we can say that the chain of responsibility design pattern creates a chain of receiver objects for a given request. In this design pattern, normally, each receiver contains a reference to the next receiver. If one receiver cannot handle the request, it passes the same request to the next receiver, and so on. In this case, one receiver can handle the request in the chain, or one or more receivers can handle the request.

Components of Chain of Resposibility Pattern

1. Handler Interface (or Abstract Class): This defines a common interface for all handlers. It typically includes a method for handling requests and a reference to the next handler in the chain.
2. Concrete Handlers: These are the actual handlers in the chain. Each handler implements the Handler interface and contains logic to handle requests. If it can't handle a request, it passes it to the next handler in the chain.
3. Client: This initiates the request and sends it to the first handler in the chain.

Mediator Design Pattern in C#

The Mediator Design Pattern is a behavioral design pattern that promotes loose coupling between objects by encapsulating how they interact. It centralizes complex communication logic between multiple objects into a mediator object, thus reducing direct dependencies between them. This promotes easier maintenance and scalability of the system.

The Mediator Design Pattern restricts direct communications between the objects and forces them to collaborate only via a mediator object. This pattern is used to centralize complex communications and control between related objects in a system. The Mediator object acts as the communication center for all objects. That means when an object needs to communicate with another object, it does not call the other object directly. Instead, it calls the mediator object, and it is the responsibility of the mediator object to route the message to the destination object.

Components of Mediator Design Pattern

1. Mediator: Defines an interface for communication between colleague objects.
2. Colleague: It is an abstract class, and Concrete Colleague classes will implement this abstract class.
3. ConcreteMediator: Implements the mediator interface, coordinating communication between colleague objects.
4. ConcreteColleague: Implements the colleague interface and communicates with other colleagues through the mediator.

Template Method Design Pattern in C#

The Template Method Design Pattern is a behavioral design pattern that defines the skeleton of an algorithm in the superclass but lets subclasses override specific steps of the algorithm without changing its structure. It allows reusing common behavior across multiple classes while still allowing customization where necessary.

Components of Template Method Design Pattern

• Abstract Class: This class defines the template method, which is the skeleton of the algorithm. It consists of several abstract methods that subclasses must implement.
• Concrete Classes: These classes inherit from the abstract class and provide implementations for the abstract methods.

Command Design Pattern in C#

The Command Design Pattern is a behavioral design pattern that encapsulates a request as an object, thereby allowing parameterization of clients with queues, requests, and operations. This pattern decouples sender and receiver of a request based on a command, which helps in invoking the right method at the right time without knowing the actual implementation details.

Components of Command Design Pattern

1. Command: Defines an interface for executing an operation.
2. Concrete Command: Implements the Command interface and binds a receiver with an action. It defines a binding between the action and the receiver.
3. Invoker: Requests the command to execute the operation.
4. Receiver: Knows how to perform the operation.

Observer Design Pattern in C#

The Observer Design Pattern is a behavioral design pattern that defines a one-to-many dependency between objects. When one object (the subject) changes its state, all its dependents (observers) are notified and updated automatically. This pattern is widely used in software engineering to establish communication between objects in a loosely coupled manner.

This Design Pattern is widely used for implementing distributed event-handling systems where an object needs to notify other objects about its state changes without knowing who these objects are.

In the Observer Design Pattern, an object (called a Subject) maintains a list of its dependents (called Observers). It notifies them automatically whenever any state changes by calling one of their methods. The Other names of this pattern are Producer/Consumer and Publish/Subscribe.

Components of Bridge Design Pattern

1. Subject: This is the object that is being observed. It maintains a list of observers and provides methods to attach, detach, and notify observers of state changes.
2. Observer: This is the interface that defines the method(s) that the subject will use to notify observers of state changes.
3. ConcreteSubject: This is the concrete implementation of the subject. It maintains the state of interest and notifies observers when changes occur.
4. ConcreteObserver: This is the concrete implementation of the observer. It registers itself with the subject and implements the update method to react to changes in the subject's state.