Usage Of Dependency Injection (DI) Design Pattern | Design Patterns Tutorial

In Object Oriented Programming paradigm, objects work together in a collaboration model where there are contributors and consumers. Naturally, this communication model generates dependencies between objects and components, becoming difficult to manage when complexity increases.
Class dependencies and model complexity
Class dependencies and model complexity
In Factory Pattern, the separation between the interface and the implementation using services, where the client objects are often responsible for service location.
The Dependency Injection pattern is a particular implementation of Inversion of Control. Inversion of Control (IoC) means that objects do not create other objects on which they rely to do their work. Instead, they get the objects that they need from an outside source (for example, an xml configuration file).
Dependency Injection (DI) means that this is done without the object intervention, usually by a framework component that passes constructor parameters and set properties.

The Dependency Injection (DI) Design Pattern

At a high level, the goal of Dependency Injection is that a client class (e.g. the golfer) needs something that satisfies an interface (e.g. IClub). It doesn't care what the concrete type is (e.g. WoodClub, IronClub, WedgeClub orPutterClub), it wants someone else to handle that (e.g. a good caddy). The Dependency Resolver in ASP.NET MVC can allow you to register your dependency logic somewhere else (e.g. a container or a bag of clubs).
Dependency Injection diagram
Dependency Injection - Golf analogy
The advantages of using Dependency Injection pattern and Inversion of Control are the following:
  • Reduces class coupling
  • Increases code reusing
  • Improves code maintainability
  • Improves application testing
Note: Dependency Injection is sometimes compared with Abstract Factory Design Pattern, but there is a slight difference between both approaches. DI has a Framework working behind to solve dependencies by calling the factories and the registered services.