Dependency Injection is a software development pattern where instead of directly instantiating objects, the objects required by a class are passed in. This helps with maintaining code flexibility, writing unit test cases etc…
The first and foremost thing is to define interfaces and then write implementations. This way, the consuming code needs to know about the methods to be invoked without worrying about the implementation. Software known as Dependency Injection container takes care of instantiating the actual objects as long as the bindings are defined.
This blog post is not about Dependency Injection or Unit Tests but more about how to use Dependency Injection in ASP.Net MVC Core. ASP.Net MVC Core comes with an in-built DI container and supports constructor-based injection i.e instances are passed into the constructor of the consuming class.
There are 3 scopes for objects:
Transient: Every time a class needs an object, a new instance of the requested object is instantiated and passed in. i.e for example if there are 3 classes that need an instance of IService, each class will receive it’s own copy every time even if the three classes are used as part of the same request/response.
Scoped: One object for a particular type is created per request/response and the same object is passed into every class that requests the object processing one request/response cycle.
Singleton: One instance of the class is instantiated for the entire lifetime of the application and the same instance is passed for every class in every request/response cycle.
The use cases for each would vary. Scoped is the default i.e one object for a given type for every class in the same request/response cycle.
Singleton’s are useful in cases such as IConfiguration where the same class can be passed around for getting config information rather than having multiple instances.
Interfaces and implementation classes can be registered by calling the following methods on IServiceCollection for example
AddSingleton<IInterface, Implementation>();
AddScoped<IInterface, Implementation>();
AddTransient<IInterface, Implementation>();or in Singleton if the object is already instantiated, the object can be passed in by calling:
AddSingleton<IInterface>(instance);–
Mr. Kanti Kalyan Arumilli
B.Tech, M.B.A
Founder & CEO, Lead Full-Stack .Net developer
ALight Technology And Services Limited
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