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<h1 id="ContentTitle" class="content-heading">Design Patterns In C# .NET</h1>
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<li class="publish-time" title="Updated Date" style="color: #666;"> Updated date <span id="PublishDate"><span class="year">Jun 17, 2021</span></span>
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<p id="ArticleSummary" style="display: none;" class="article-summary">In this tutorial, learn everything about design patterns in C# and how to Implement design patterns using C# and .NET. Factory design pattern, Abstract Factory design
pattern, Builder design pattern, Prototype design pattern, Singleton design pattern.</p>
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<h2>Design Patterns In C#</h2>
<p>Design patterns provide general solutions or a flexible way to solve common design problems. This article provides an introduction of design patterns and how design patterns are implemented in C# and .NET.</p>
<p>Before starting with design patterns in .NET, let's understand what is the meaning of design patterns and why they are useful in software architecture and programming.</p>
<h2>What are Design Patterns in Software Development?</h2>
<p>Design Patterns in the object-oriented world is a reusable solution to common software design problems that occur repeatedly in real-world application development. It is a template or description of how to solve problems that can
be used in many situations.</p>
<p>"<em>A pattern is a recurring solution to a problem in a context.</em>"</p>
<p>"<em>Each pattern describes a problem that occurs over and over again in our environment, and then describes the core of the solution to that problem, in such a way that you can use this solution a million times over, without ever
doing it the same way twice.</em>" - Christopher Alexander, <em>A Pattern Language</em>.</p>
<p>Patterns are used by developers for their specific designs to solve their problems. Pattern choice and usage among various design patterns depends on individual needs and problems. Design patterns are a very powerful tool for software
developers. It is important to understand design patterns rather than memorizing their classes, methods, and properties. It is also important to learn how to apply patterns to specific problems to get the desired result. This will be
the required continuous practice for using and applying design patterns in day to day software development. First, identify the software design problem then see how to address these problems using design patterns and determine the
best-suited design problem to solve the problem.</p>
<p>There are 23 design patterns, also known as Gang of Four (GoF) design patterns. The Gang of Four is the authors of the book, "Design Patterns: Elements of Reusable Object-Oriented Software". These 23 patterns are grouped into three
main categories:</p>
<p style="text-align: center;"><img alt="Design Patterns In CSharp" class="" data-src="https://csharpcorner-mindcrackerinc.netdna-ssl.com/UploadFile/bd5be5/design-patterns-in-net/Images/Design Patterns In DotNet.jpg"
src="https://csharpcorner-mindcrackerinc.netdna-ssl.com/UploadFile/bd5be5/design-patterns-in-net/Images/Design Patterns In DotNet.jpg"></p>
<h2>Creational Design Pattern</h2>
<ol>
<li>Factory Method</li>
<li>Abstract Factory</li>
<li>Builder</li>
<li>Prototype</li>
<li>Singleton</li>
</ol>
<h2>Structural Design Patterns</h2>
<ol>
<li>Adapter</li>
<li>Bridge</li>
<li>Composite</li>
<li>Decorator</li>
<li>Façade</li>
<li>Flyweight</li>
<li>Proxy</li>
</ol>
<h2>Behavioral Design Patterns</h2>
<ol>
<li>Chain of Responsibility</li>
<li>Command</li>
<li>Interpreter</li>
<li>Iterator</li>
<li>Mediator</li>
<li>Memento</li>
<li>Observer</li>
<li>State</li>
<li>Strategy</li>
<li>Visitor</li>
<li>Template Method</li>
</ol>
<p>In this article, we are learning and understanding Creational Design Patterns in detail including UML diagram, template source code and a real-world example in C#. Creational Design Patterns provide ways to instantiate a single object
or group of related objects. These patterns deal with the process of object creation in such a way that they are separated from their implementing system. That provides more flexibility in deciding which object needs to be created or
instantiated for a given scenario. There are the following five such patterns.</p>
<h2>Abstract Factory</h2>
<p>This creates a set of related objects or dependent objects. The "family" of objects created by the factory is determined at run-time depending on the selection of concrete factory classes.</p>
<p>An abstract factory pattern acts as a super-factory that creates other factories. An abstract factory interface is responsible for creating a set of related objects or dependent objects without specifying their concrete classes.
</p>
<p>The UML class diagram below describes an implementation of the abstract factory design pattern.</p>
<p style="text-align: center;"><img alt="Design Patterns In .NET" border="0" class="lazy" data-src="https://csharpcorner-mindcrackerinc.netdna-ssl.com/UploadFile/bd5be5/design-patterns-in-net/Images/Design-Patterns-1.jpg"
style="height:423px; width:650px"></p>
<p>The classes, objects, and interfaces used in the above UML diagram are described below.</p>
<ol>
<li><em>Client</em> This class uses the Abstract Factory and Abstract Product interfaces to create a family of related objects.</li>
<li><em>Abstract Factory</em> This is an interface that creates abstract products.</li>
<li><em>Abstract Product</em> This is an interface that declares a type of product.</li>
<li><em>Concrete Factory </em> This is a class that implements the abstract factory interface to create concrete products.</li>
<li><em>Concrete Product </em> This is a class that implements the abstract product interface to create products.</li>
</ol>
<p>The following code shows the basic template code of the abstract factory design pattern implemented using C#:</p>
<p style="text-align: center;"><img alt="Design Patterns In .NET" border="0" class="lazy" data-src="https://csharpcorner-mindcrackerinc.netdna-ssl.com/UploadFile/bd5be5/design-patterns-in-net/Images/Design-Patterns-2.jpg"
style="height:568px; width:493px"></p>
<p style="text-align: center;"><img alt="Design Patterns In .NET" border="0" class="lazy" data-src="https://csharpcorner-mindcrackerinc.netdna-ssl.com/UploadFile/bd5be5/design-patterns-in-net/Images/Design-Patterns-3.jpg"
style="height:329px; width:476px"></p>
<p>In the above abstract factory design pattern, the source code template client has two private fields that hold the instances of abstract product classes. These objects will be accessed by inheriting their base class interface. When the
client is instantiated, a concrete factory object is passed to its constructor and populate private fields of the client with appropriate data or values.</p>
<p>The Abstractfactory is a base class for concrete factory classes that generate or create a set of related objects. This base class contains the definition of a method for each type of object that will be instantiated. The base class is
declared as Abstract so that it can be inherited by other concrete factory subclasses.</p>
<p>The concrete factory classes are inheriting from the Abstractfactory class and override the method of the base class to generate a set of related objects required by the client. There can be a specified number of concrete factory
classes depending on the software or application requirements.</p>
<p>Abstractproduct is a base class for the types of objects that the factory class can create. There should be one base type for every distinct type of product required by the client.</p>
<p>The concrete product classes are inheriting from Abstractproduct class. Each class contains specific functionality. Objects of these classes are generated by abstractfactory classes to populate the client.</p>
<h2>A real-world example of Abstract factory design pattern using C#</h2>
<p>As an example, consider a system that does the packaging and delivery of items for a web-based store. The company delivers two types of products. The first is a standard product that is placed in a box and delivered through the post
with a simple label. The second is a delicate item that requires shock-proof packaging and is delivered via a courier. In this situation, there are two types of objects required, a packaging object and a delivery documentation object.
We could use two factories to generate these related objects. The one factory will be responsible for creating packaging and other delivery objects for standard parcels. The second will be responsible for creating packaging and delivery
objects for delicate parcels. <strong>Class Client </strong></p>
<p style="text-align: center;"><strong><strong><img alt="Design Patterns In .NET" border="0" class="lazy" data-src="https://csharpcorner-mindcrackerinc.netdna-ssl.com/UploadFile/bd5be5/design-patterns-in-net/Images/Design-Patterns-4.jpg"
style="height:483px; width:512px"></strong></strong></p>
<p style="text-align: center;"><strong><strong><img alt="Design Patterns In .NET" border="0" class="lazy" data-src="https://csharpcorner-mindcrackerinc.netdna-ssl.com/UploadFile/bd5be5/design-patterns-in-net/Images/Design-Patterns-5.jpg"
style="height:474px; width:490px"></strong></strong></p>
<p><strong>AbstractFactory Patterns Form </strong></p>
<p style="text-align: center;"><strong><strong><img alt="Design Patterns In .NET" border="0" class="lazy" data-src="https://csharpcorner-mindcrackerinc.netdna-ssl.com/UploadFile/bd5be5/design-patterns-in-net/Images/Design-Patterns-6.jpg"
style="height:521px; width:538px"></strong></strong></p>
<p><strong>Output</strong></p>
<p style="text-align: center;"><img alt="Design Patterns In .NET" border="0" class="lazy" data-src="https://csharpcorner-mindcrackerinc.netdna-ssl.com/UploadFile/bd5be5/design-patterns-in-net/Images/Design-Patterns-7.jpg"
style="height:297px; width:518px"></p>
<p>The example code above creates two client objects, each passing to a different type of factory constructor. Types of generated objects are accessed through the client's properties. </p>
<p><strong>Note</strong> While studying abstract factory patterns, one question is, what are concrete classes? So I Googled that and the following is the answer to my question. A concrete class is nothing but a normal class that has all
basic class features, like variables, methods, constructors, and so on. We can create an instance of the class in other classes.</p>
<p>Here is a detailed article on <a href="https://www.c-sharpcorner.com/article/abstract-factory-design-pattern-in-c-sharp/" target="_blank">Abstract Factory Design Pattern In C#</a></p>
<h2>Singleton Design Pattern</h2>
<p>The Singleton design pattern is one of the simplest design patterns. This pattern ensures that the class has only one instance and provides a global point of access to it. The pattern ensures that only one object of a specific class is
ever created. All further references to objects of the singleton class refer to the same underlying instance.</p>
<p>There are situations in a project where we want only one instance of the object to be created and shared among the clients. No client can create an instance from outside. It is more appropriate than creating a global variable since
this may be copied and leads to multiple access points.</p>
<p>The UML class diagram below describes an implementation of the abstract factory design pattern:</p>
<p style="text-align: center;"><img alt="Design Patterns In .NET" border="0" class="lazy" data-src="https://csharpcorner-mindcrackerinc.netdna-ssl.com/UploadFile/bd5be5/design-patterns-in-net/Images/Design-Patterns-8.jpg"
style="height:236px; width:404px"></p>
<p>In the singleton patterns, the UML diagram above the "GetInstace" method should be declared as static. This method returns a single instance held in a private "instance" variable. In the singleton pattern, all the methods and
instances are defined as static. The static keyword ensures that only one instance of the object is created and you can call methods of the class without creating an object.</p>
<p>The constructor of a class is marked as private. This prevents any external classes from creating new instances. The class is also sealed to prevent inheritance, which could lead to subclassing that breaks the singleton rules.
</p>
<p>The following code shows the basic template code of the singleton design pattern implemented using C#.</p>
<p><strong>The eager initialization of singleton pattern </strong></p>
<p style="text-align: center;"><strong><strong><img alt="Design Patterns In .NET" border="0" class="lazy" data-src="https://csharpcorner-mindcrackerinc.netdna-ssl.com/UploadFile/bd5be5/design-patterns-in-net/Images/Design-Patterns-9.jpg"
style="height:389px; width:469px"></strong></strong></p>
<p><strong>Lazy initialization of singleton pattern </strong></p>
<p style="text-align: center;"><strong><strong><img alt="Design Patterns In .NET" border="0" class="lazy" data-src="https://csharpcorner-mindcrackerinc.netdna-ssl.com/UploadFile/bd5be5/design-patterns-in-net/Images/Design-Patterns-10.jpg"
style="height:414px; width:450px"></strong></strong></p>
<p><strong>Thread-safe (Double-checked Locking) initialization of singleton pattern </strong></p>
<p style="text-align: center;"><strong><strong><img alt="Design Patterns In .NET" border="0" class="lazy" data-src="https://csharpcorner-mindcrackerinc.netdna-ssl.com/UploadFile/bd5be5/design-patterns-in-net/Images/Design-Patterns-11.jpg"
style="height:490px; width:442px"></strong></strong></p>
<p>The code above shows the "lockThis" object and the use of locking within the "GetInstance" method. Since programs can be multithreaded, it is possible that two threads could request the singleton before the instance variable is
initialized. By locking the dummy "lockThis" variable, all other threads will be blocked. This means that two threads will not be able to simultaneously create their own copies of the object.</p>
<h2>A real-world example of Abstract factory design pattern using C#.net</h2>
<p>I am trying to apply this pattern in my application where I want to maintain an application state for user login information and any other specific information that is required to be instantiated only once and held in only one
instance. </p>
<p><strong>Class ApplicationState </strong></p>
<p style="text-align: center;"><strong><strong><img alt="Design Patterns In .NET" border="0" class="lazy" data-src="https://csharpcorner-mindcrackerinc.netdna-ssl.com/UploadFile/bd5be5/design-patterns-in-net/Images/Design-Patterns-12.jpg"
style="height:533px; width:446px"></strong></strong></p>
<p><strong>Singleton pattern form</strong></p>
<p style="text-align: center;"><strong><strong><img alt="Design Patterns In .NET" border="0" class="lazy" data-src="https://csharpcorner-mindcrackerinc.netdna-ssl.com/UploadFile/bd5be5/design-patterns-in-net/Images/Design-Patterns-13.jpg"
style="height:527px; width:564px"></strong></strong></p>
<p><strong>Output </strong></p>
<p style="text-align: center;"><strong><strong><img alt="Design Patterns In .NET" border="0" class="lazy" data-src="https://csharpcorner-mindcrackerinc.netdna-ssl.com/UploadFile/bd5be5/design-patterns-in-net/Images/Design-Patterns-14.jpg"
style="height:262px; width:452px"></strong></strong></p>
<p>The preceding sample code creates two new variables and assigns the return value of the GetState method to each. They are then compared to check that they both contain the same values and a reference to the same object.</p>
<p>Here is a detailed article on <a href="https://www.c-sharpcorner.com/article/abstract-factory-design-pattern-in-c-sharp/" target="_blank">Abstract Factory Design Pattern In C#</a></p>
<p><strong>Interview Questions </strong></p>
<p>Going for an interview, here are <a href="https://www.c-sharpcorner.com/UploadFile/questpond/design-pattern-interview-questions/" target="_blank">Interview Questions on Design Patterns.</a> </p>
<h2>Summary </h2>
<p>I hope this article gives you an introduction to design patterns and various types of design patterns used in .Net.</p>
<p>In this article, we learned the Abstract Factory and Singleton Design Patterns in detail. The remaining patterns of the Creational Design Pattern Group will be explained in my next article.</p>
<p><strong>Recommended Articles</strong></p>
<p>Here is a list of some highly recommended articles related to design patterns. </p>
<ol>
<li><a href="https://www.c-sharpcorner.com/article/factory-method-design-pattern-in-c-sharp/" target="_blank">Abstract Factory Design Pattern In C#</a></li>
<li><a href="https://www.c-sharpcorner.com/article/factory-method-design-pattern-in-c-sharp/" target="_blank">Factory Method Design Pattern In C#</a> </li>
<li><a href="https://www.c-sharpcorner.com/UploadFile/8911c4/singleton-design-pattern-in-C-Sharp/" target="_blank">Singleton Design Pattern In C#</a></li>
<li><a href="https://www.c-sharpcorner.com/UploadFile/dacca2/design-pattern-for-beginner-bridge-design-pattern/" target="_blank">Bridge Design Pattern In C#</a></li>
<li><a href="https://www.c-sharpcorner.com/UploadFile/dacca2/design-pattern-for-beginner-part-3-prototype-design-patter/" target="_blank">Prototype Design Pattern In C#</a></li>
<li><a href="https://www.c-sharpcorner.com/UploadFile/dacca2/design-pattern-for-beginners-part-4-decorator-design-patt/" target="_blank">Decorator Design Pattern In C#</a></li>
<li><a href="https://www.c-sharpcorner.com/UploadFile/dacca2/design-pattern-for-beginner-part-5-composite-design-patter/" target="_blank">Composite Design Pattern In C#</a></li>
</ol>
<p>Here is a list of more <a href="https://www.c-sharpcorner.com/UploadFile/dacca2/design-pattern-for-beginners-part-6-adaptor-design-patter/" target="_blank">Design Patterns In C#.</a></p>
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<div data-comment="" class="commentDescription">You forgot to mention "Repository Design Patterns". It would be great if you add "Repository Design Patterns" here!</div>
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<div data-comment="" class="commentDescription">Thanks @Kanchan Naik for sharing this article.</div>
<div class="comment-info clearfix"> <span class="comment-time"> <i class="d-icon icon-clock-small"></i>Dec 12, 2020</span><a href="https://www.c-sharpcorner.com/members/shivaji-kakad2" alt="Shivaji Kakad">Shivaji Kakad</a>
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<div data-comment="" class="commentDescription">Easy to understand and nice explanation.</div>
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2020</span><a href="https://www.c-sharpcorner.com/members/mahesh-pullagura" alt="Mahesh Pullagura">Mahesh Pullagura</a></div>
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<div data-comment="" class="commentDescription">Nice explanation</div>
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<div data-comment="" class="commentDescription">Nice article</div>
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<div data-comment="" class="commentDescription">Very good article,really useful for beginners</div>
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<div data-comment="" class="commentDescription">Thanks Kanchan</div>
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2019</span><a href="https://www.c-sharpcorner.com/members/mohammad-naderi3" alt="Mohammad Naderi">Mohammad Naderi</a></div>
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<div data-comment="" class="commentDescription">Good one, But its wrong about double check lock. Idea of double check lock is minimum number of threads have to wait and that’s only for first time. As name implies we check
whether instance is null twice, that's before obtain the lock if its not null we return without locking. Lock is accrued only needed (second check is for that). Here I updated your sample :- public class Singleton {
private static Singleton instance = null; private Singleton() { } private static object lockThis = new object(); public static Singleton GetInstance { get { if (instance == null) { lock (lockThis) { if (instance == null)
instance = new Singleton(); } } return instance; } } }</div>
<div class="comment-info clearfix"> <span class="comment-time"> <i class="d-icon icon-clock-small"></i>Mar 19,
2019</span><a href="https://www.c-sharpcorner.com/members/eranda-horanagama" alt="Eranda Horanagama">Eranda Horanagama</a></div>
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<div data-comment="" class="commentDescription">Thank you, Eranda. Would you like to help us correct this code? What code will your code replace? Thanks.</div>
<div class="comment-info clearfix"> <span class="comment-time"> <i class="d-icon icon-clock-small"></i>Mar 27,
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<div data-comment="" class="commentDescription">Thanks <a target="_blank" class="LinkNormalBlue" href="https://www.c-sharpcorner.com/members/eranda-horanagama">Eranda Horanagama</a>, you are absolutely right!</div>
<div class="comment-info clearfix"> <span class="comment-time"> <i class="d-icon icon-clock-small"></i>Dec 12,
2020</span><a href="https://www.c-sharpcorner.com/members/shivaji-kakad2" alt="Shivaji Kakad">Shivaji Kakad</a></div>
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<div data-comment="" class="commentDescription">Nice one need more information on other patterns</div>
<div class="comment-info clearfix"> <span class="comment-time"> <i class="d-icon icon-clock-small"></i>Dec 28, 2018</span><a href="https://www.c-sharpcorner.com/members/vaibhav-mayee" alt="vaibhav mayee">vaibhav mayee</a>
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<div data-comment="" class="commentDescription">Abstract factory pattern can also be implemented using Interface, then why Abstract came into picture? Any specific benefit of having Abstract class instead of Interface.</div>
<div class="comment-info clearfix"> <span class="comment-time"> <i class="d-icon icon-clock-small"></i>Dec 01, 2018</span><a href="https://www.c-sharpcorner.com/members/snehlata-shaw" alt="Snehlata Shaw">Snehlata Shaw</a>
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<div data-comment="" class="commentDescription">Since it is an Abstract class, we will be able to take advantage of inheritance. Write all functions working on the abstract of the underlying products in the Abstract
factory created.</div>
<div class="comment-info clearfix"> <span class="comment-time"> <i class="d-icon icon-clock-small"></i>Dec 03,
2018</span><a href="https://www.c-sharpcorner.com/members/arish-saseendran" alt="Arish Saseendran">Arish Saseendran</a></div>
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<div data-comment="" class="commentDescription">It's a small advantage over interface to pack the functions together</div>
<div class="comment-info clearfix"> <span class="comment-time"> <i class="d-icon icon-clock-small"></i>Dec 03,
2018</span><a href="https://www.c-sharpcorner.com/members/arish-saseendran" alt="Arish Saseendran">Arish Saseendran</a></div>
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<div data-comment="" class="commentDescription">In Object Oriented Programming, abstraction can be implemented with two approaches - either using Abstract base classes or with interfaces. For all practical purposes,
interfaces are "parent classes" just like Abstract base classes - you can declare a variable of the interface type, and have it pointed to one of the derivative class instances. Hence, both can be used to implement
Abstract Factory pattern.</div>
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DESIGN PATTERNS IN C# .NET
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In this tutorial, learn everything about design patterns in C# and how to
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Factory design pattern, Builder design pattern, Prototype design pattern,
Singleton design pattern.
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Designpatterns.rar
DESIGN PATTERNS IN C#
Design patterns provide general solutions or a flexible way to solve common
design problems. This article provides an introduction of design patterns and
how design patterns are implemented in C# and .NET.
Before starting with design patterns in .NET, let's understand what is the
meaning of design patterns and why they are useful in software architecture and
programming.
WHAT ARE DESIGN PATTERNS IN SOFTWARE DEVELOPMENT?
Design Patterns in the object-oriented world is a reusable solution to common
software design problems that occur repeatedly in real-world application
development. It is a template or description of how to solve problems that can
be used in many situations.
"A pattern is a recurring solution to a problem in a context."
"Each pattern describes a problem that occurs over and over again in our
environment, and then describes the core of the solution to that problem, in
such a way that you can use this solution a million times over, without ever
doing it the same way twice." - Christopher Alexander, A Pattern Language.
Patterns are used by developers for their specific designs to solve their
problems. Pattern choice and usage among various design patterns depends on
individual needs and problems. Design patterns are a very powerful tool for
software developers. It is important to understand design patterns rather than
memorizing their classes, methods, and properties. It is also important to learn
how to apply patterns to specific problems to get the desired result. This will
be the required continuous practice for using and applying design patterns in
day to day software development. First, identify the software design problem
then see how to address these problems using design patterns and determine the
best-suited design problem to solve the problem.
There are 23 design patterns, also known as Gang of Four (GoF) design patterns.
The Gang of Four is the authors of the book, "Design Patterns: Elements of
Reusable Object-Oriented Software". These 23 patterns are grouped into three
main categories:
CREATIONAL DESIGN PATTERN
1. Factory Method
2. Abstract Factory
3. Builder
4. Prototype
5. Singleton
STRUCTURAL DESIGN PATTERNS
1. Adapter
2. Bridge
3. Composite
4. Decorator
5. Façade
6. Flyweight
7. Proxy
BEHAVIORAL DESIGN PATTERNS
1. Chain of Responsibility
2. Command
3. Interpreter
4. Iterator
5. Mediator
6. Memento
7. Observer
8. State
9. Strategy
10. Visitor
11. Template Method
In this article, we are learning and understanding Creational Design Patterns in
detail including UML diagram, template source code and a real-world example in
C#. Creational Design Patterns provide ways to instantiate a single object or
group of related objects. These patterns deal with the process of object
creation in such a way that they are separated from their implementing system.
That provides more flexibility in deciding which object needs to be created or
instantiated for a given scenario. There are the following five such patterns.
ABSTRACT FACTORY
This creates a set of related objects or dependent objects. The "family" of
objects created by the factory is determined at run-time depending on the
selection of concrete factory classes.
An abstract factory pattern acts as a super-factory that creates other
factories. An abstract factory interface is responsible for creating a set of
related objects or dependent objects without specifying their concrete classes.
The UML class diagram below describes an implementation of the abstract factory
design pattern.
The classes, objects, and interfaces used in the above UML diagram are described
below.
1. Client This class uses the Abstract Factory and Abstract Product interfaces
to create a family of related objects.
2. Abstract Factory This is an interface that creates abstract products.
3. Abstract Product This is an interface that declares a type of product.
4. Concrete Factory This is a class that implements the abstract factory
interface to create concrete products.
5. Concrete Product This is a class that implements the abstract product
interface to create products.
The following code shows the basic template code of the abstract factory design
pattern implemented using C#:
In the above abstract factory design pattern, the source code template client
has two private fields that hold the instances of abstract product classes.
These objects will be accessed by inheriting their base class interface. When
the client is instantiated, a concrete factory object is passed to its
constructor and populate private fields of the client with appropriate data or
values.
The Abstractfactory is a base class for concrete factory classes that generate
or create a set of related objects. This base class contains the definition of a
method for each type of object that will be instantiated. The base class is
declared as Abstract so that it can be inherited by other concrete factory
subclasses.
The concrete factory classes are inheriting from the Abstractfactory class and
override the method of the base class to generate a set of related objects
required by the client. There can be a specified number of concrete factory
classes depending on the software or application requirements.
Abstractproduct is a base class for the types of objects that the factory class
can create. There should be one base type for every distinct type of product
required by the client.
The concrete product classes are inheriting from Abstractproduct class. Each
class contains specific functionality. Objects of these classes are generated by
abstractfactory classes to populate the client.
A REAL-WORLD EXAMPLE OF ABSTRACT FACTORY DESIGN PATTERN USING C#
As an example, consider a system that does the packaging and delivery of items
for a web-based store. The company delivers two types of products. The first is
a standard product that is placed in a box and delivered through the post with a
simple label. The second is a delicate item that requires shock-proof packaging
and is delivered via a courier. In this situation, there are two types of
objects required, a packaging object and a delivery documentation object. We
could use two factories to generate these related objects. The one factory will
be responsible for creating packaging and other delivery objects for standard
parcels. The second will be responsible for creating packaging and delivery
objects for delicate parcels. Class Client
AbstractFactory Patterns Form
Output
The example code above creates two client objects, each passing to a different
type of factory constructor. Types of generated objects are accessed through the
client's properties.
Note While studying abstract factory patterns, one question is, what are
concrete classes? So I Googled that and the following is the answer to my
question. A concrete class is nothing but a normal class that has all basic
class features, like variables, methods, constructors, and so on. We can create
an instance of the class in other classes.
Here is a detailed article on Abstract Factory Design Pattern In C#
SINGLETON DESIGN PATTERN
The Singleton design pattern is one of the simplest design patterns. This
pattern ensures that the class has only one instance and provides a global point
of access to it. The pattern ensures that only one object of a specific class is
ever created. All further references to objects of the singleton class refer to
the same underlying instance.
There are situations in a project where we want only one instance of the object
to be created and shared among the clients. No client can create an instance
from outside. It is more appropriate than creating a global variable since this
may be copied and leads to multiple access points.
The UML class diagram below describes an implementation of the abstract factory
design pattern:
In the singleton patterns, the UML diagram above the "GetInstace" method should
be declared as static. This method returns a single instance held in a private
"instance" variable. In the singleton pattern, all the methods and instances
are defined as static. The static keyword ensures that only one instance of the
object is created and you can call methods of the class without creating an
object.
The constructor of a class is marked as private. This prevents any external
classes from creating new instances. The class is also sealed to prevent
inheritance, which could lead to subclassing that breaks the singleton rules.
The following code shows the basic template code of the singleton design pattern
implemented using C#.
The eager initialization of singleton pattern
Lazy initialization of singleton pattern
Thread-safe (Double-checked Locking) initialization of singleton pattern
The code above shows the "lockThis" object and the use of locking within the
"GetInstance" method. Since programs can be multithreaded, it is possible that
two threads could request the singleton before the instance variable is
initialized. By locking the dummy "lockThis" variable, all other threads will be
blocked. This means that two threads will not be able to simultaneously create
their own copies of the object.
A REAL-WORLD EXAMPLE OF ABSTRACT FACTORY DESIGN PATTERN USING C#.NET
I am trying to apply this pattern in my application where I want to maintain an
application state for user login information and any other specific information
that is required to be instantiated only once and held in only one instance.
Class ApplicationState
Singleton pattern form
Output
The preceding sample code creates two new variables and assigns the return value
of the GetState method to each. They are then compared to check that they both
contain the same values and a reference to the same object.
Here is a detailed article on Abstract Factory Design Pattern In C#
Interview Questions
Going for an interview, here are Interview Questions on Design Patterns.
SUMMARY
I hope this article gives you an introduction to design patterns and various
types of design patterns used in .Net.
In this article, we learned the Abstract Factory and Singleton Design Patterns
in detail. The remaining patterns of the Creational Design Pattern Group will be
explained in my next article.
Recommended Articles
Here is a list of some highly recommended articles related to design patterns.
1. Abstract Factory Design Pattern In C#
2. Factory Method Design Pattern In C#
3. Singleton Design Pattern In C#
4. Bridge Design Pattern In C#
5. Prototype Design Pattern In C#
6. Decorator Design Pattern In C#
7. Composite Design Pattern In C#
Here is a list of more Design Patterns In C#.
* Abstract Design patterns
* C# Design patterns
* Factory Design patterns
* Singleton Design patterns
* Structural Design Patterns
Next Recommended Reading Adapter and Facade Design Pattern in C#
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You forgot to mention "Repository Design Patterns". It would be great if you add
"Repository Design Patterns" here!
Nov 10, 2021Pranam Bhat
465 4.8k 653.5k
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Thanks @Kanchan Naik for sharing this article.
Dec 12, 2020Shivaji Kakad
1993 88 0
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Easy to understand and nice explanation.
Nov 07, 2020Mahesh Pullagura
1815 266 0
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Nice explanation
Nov 10, 2019Dushyant Patel
1932 149 0
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Nice article
Sep 13, 2019Pankaj Patel
91 23.4k 1.3m
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Very good article,really useful for beginners
Aug 23, 2019rajesh raj
2022 59 0
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Thanks Kanchan
Aug 06, 2019Mohammad Naderi
2018 63 0
* 1
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Good one, But its wrong about double check lock. Idea of double check lock is
minimum number of threads have to wait and that’s only for first time. As name
implies we check whether instance is null twice, that's before obtain the lock
if its not null we return without locking. Lock is accrued only needed (second
check is for that). Here I updated your sample :- public class Singleton {
private static Singleton instance = null; private Singleton() { } private static
object lockThis = new object(); public static Singleton GetInstance { get { if
(instance == null) { lock (lockThis) { if (instance == null) instance = new
Singleton(); } } return instance; } } }
Mar 19, 2019Eranda Horanagama
974 1.5k 610.4k
* 2
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* Reply
Thank you, Eranda. Would you like to help us correct this code? What code will
your code replace? Thanks.
Mar 27, 2019Mahesh Chand
Admin 343.3k 208.9m
* 1
Thanks Eranda Horanagama, you are absolutely right!
Dec 12, 2020Shivaji Kakad
1993 88 0
* 0
Nice one need more information on other patterns
Dec 28, 2018vaibhav mayee
1959 122 0
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* Reply
Abstract factory pattern can also be implemented using Interface, then why
Abstract came into picture? Any specific benefit of having Abstract class
instead of Interface.
Dec 01, 2018Snehlata Shaw
2077 4 0
* 0
* 3
* Reply
Since it is an Abstract class, we will be able to take advantage of inheritance.
Write all functions working on the abstract of the underlying products in the
Abstract factory created.
Dec 03, 2018Arish Saseendran
2072 9 0
* 0
It's a small advantage over interface to pack the functions together
Dec 03, 2018Arish Saseendran
2072 9 0
* 0
In Object Oriented Programming, abstraction can be implemented with two
approaches - either using Abstract base classes or with interfaces. For all
practical purposes, interfaces are "parent classes" just like Abstract base
classes - you can declare a variable of the interface type, and have it pointed
to one of the derivative class instances. Hence, both can be used to implement
Abstract Factory pattern.
Dec 28, 2020Dinesh Muciliath Jayadevan
2079 2 0
* 0
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