Difference between design patterns ?

Question

Hi, Could you please help me to understand the difference between Factory design pattern and Dependency injection...? As in both we create interface and that will implement through some classes and abstract class responsible for creating objects . Thanks,

Laxmidhar Sahoo · Answer

Factory Pattern: We implement the factory design pattern in a C# program.A factory creates objects With this pattern, we develop an abstraction that isolates the logic for determining which type of class to create. The factory design pattern relies on a type hierarchy. The classes must all implement an interface or derive from a base class. We use an abstract class as the base. The Manager, Clerk and Programmer classes derive from Position. Summary. We looked the factory design pattern, which is used to instantiate objects based on another data type such as integers. Factories can be used to reduce code bloat and also make it easier to modify which objects need to be created. there are two examples using System; class Program { abstract class Position { public abstract string Title { get ; } } class Manager : Position { public override string Title { get { return "Manager" ; } } } class Clerk : Position { public override string Title { get { return "Clerk" ; } } } class Programmer : Position { public override string Title { get { return "Programmer" ; } } } static class Factory { /// /// Decides which class to instantiate. /// public static Position Get( int id) { switch (id) { case 0: return new Manager(); case 1: case 2: return new Clerk(); case 3: default : return new Programmer(); } } } static void Main() { for ( int i = 0; i { var position = Factory.Get(i); Console.WriteLine( "Where id = {0}, position = {1} " , i, position.Title); } } } Output Where id = 0, position = Manager Where id = 1, position = Clerk Where id = 2, position = Clerk Where id = 3, position = Programmer Another example using System; namespace Factory { /// /// The 'Product' interface /// public interface IFactory { void Drive( int miles); } /// /// A 'ConcreteProduct' class /// public class Scooter : IFactory { public void Drive( int miles) { Console.WriteLine( "Drive the Scooter : " + miles.ToString() + "km" ); } } /// /// A 'ConcreteProduct' class /// public class Bike : IFactory { public void Drive( int miles) { Console.WriteLine( "Drive the Bike : " + miles.ToString() + "km" ); } } /// /// The Creator Abstract Class /// public abstract class VehicleFactory { public abstract IFactory GetVehicle( string Vehicle); } /// /// A 'ConcreteCreator' class /// public class ConcreteVehicleFactory : VehicleFactory { public override IFactory GetVehicle( string Vehicle) { switch (Vehicle) { case "Scooter" : return new Scooter(); case "Bike" : return new Bike(); default : throw new ApplicationException( string .Format( "Vehicle '{0}' cannot be created" , Vehicle)); } } } /// /// Factory Pattern Demo /// class Program { static void Main( string [] args) { VehicleFactory factory = new ConcreteVehicleFactory(); IFactory scooter = factory.GetVehicle( "Scooter" ); scooter.Drive(10); IFactory bike = factory.GetVehicle( "Bike" ); bike.Drive(20); Console.ReadKey(); } } } Dependency Injection (DI) is a technique to create a dependency or dependencies outside the class that uses it. The dependencies are injected from the code that calls the class and any information about their creation are kept away from the inside of the class. This is also why DI is an implementation of the Inversion of control (IoC) principle. To further explain the dependency injection design pattern, the inversion of control Inversion of Control Principle Normally, the flow of the program logic is determined by objects that are bound to one another. With the inversion of control, the flow depends on the defined abstractions to be implemented that is built up during program execution. This principle can be achieved by techniques like dependency injection. In IoC, the code could also be linked statically during compilation to the defined interface functions, but finding the implementation of the function to execute by reading its description from external configuration instead of with a direct reference in the code itself. There are three ways can inject the objects 1- Through constructor 2- Through properties 3-Through method Example public interface IEmailService { void SendMail( string emailAddress, string message) } public class GoogleEmailService: IEmailService { public SendMail( string emailAddress, string message) { //Send an email using google } } public class OutlookEmailService: IEmailService { public void SendMail( string emailAddress, string message) { //Send an email using outlook } } public class UserLogic { private GoogleOAuthService _authService; private IEmailService _emailService; public UserLogic(IEmailSevice emailService) { _authService = new GoogleOAuthService(); _emailService = emailService; } ... } public class UserLogic { private GoogleOAuthService _authService; private IEmailService _emailService; public IEmailService EmailService { get { return _emailService; } set { _emailService = value; } } public UserLogic() { _authService = new GoogleOAuthService(); } ... } public class UserLogic { private GoogleOAuthService _authService; public UserLogic() { _authService = new GoogleOAuthService(); _emailService = new OutlookEmailService() // or Google; } public void Register( string emailAddress, string password, IEmailService emailService) { var authResult = _authService.RegisterUser(emailAddress,password); emailService.SendMail(emailAddress, authResult.ConfirmationMessage); } }

Gaurav Gahlot · Answer

Hello Sheetal, Laxmidhar has well explained the Abstract factory part. For dependency injection, I would highly recommend you check the series of articles I have written at the below URL. It will definitely help you get in depth knowledge of DI. https://www.quickdevnotes.com/tag/dependency-injection/page/2/ @Laxmidhar: Good job with factory part. However, the examples for dependency injection does not seem to be correct. I'm not sure why you would want to instantiate the dependencies like this: public class UserLogic { private GoogleOAuthService _authService; public UserLogic( IEmailSevice emailService ) { _authService = new GoogleOAuthService(); _emailService = new OutlookEmailService() // or Google; } } Because it takes away the soul purpose of using DI in the first place. I hope you would change your code samples and make them as good as factory ones. Thank you!

Mageshwaran R · Answer

Hi, please refer this link: https://www.slideshare.net/umarali1981/design-patterns-difference-between

Laxmidhar Sahoo · Answer

@Gaurav Thank you