Dependency Injection and Reflection

Yesterday i got some discussion with my Uncle, about mobile application (again) and got some issue about the app i want to build. Then the discussion drives us  into “Dependency Injection and Reflection“. My uncle said, i have to minimalize my code, he said i have to ensure that i  split the code in individual component that can be run without have any dependency with the other component.  Separate it.

“Try dependency injection and reflection.” That’s the code my uncle said, and then it means”cari dan pelajari sendiri” As usual.  Oke, feni, you’re strong enaugh.

So let’s start gooling and found some good artcile. I don’t mind what programming language to describe dependency injection, i also use different language to my different apps.

“Jangan mengotak-kotakkan dirimu hanya dalam satu bahasa pemrograman, yang penting paham logicnya. Insya Allah yang lain juga bisa. Fenifa 2017”

In software engineering, Dependency Injection is a design principle in which code creating a new object supplies the other objects that the new object depends upon for operation. This is a special case of inversion of control. Often a dependency injection framework (or “container”) is used to manage and automate the construction and lifetimes of interdependent objects.

A dependency is an object that can be used (a service). An injection is the passing of a dependency to a dependent object (a client) that would use it. The service is made part of the client’s state. Passing the service to the client, rather than allowing a client to build or find the service, is the fundamental requirement of the pattern.

Dependency injection separates the creation of a client’s dependencies from the client’s behavior, which allows program designs to be looselycoupled and to follow the dependency inversion and single responsibility principles. It directly contrasts with the service locator pattern, which allows clients to know about the system they use to find dependencies.

An injection, the basic unit of dependency injection, is not a new or a custom mechanism. It works in the same way that “parameter passing” works. Referring to “parameter passing” as an injection carries the added implication that it’s being done to isolate the client from details.

An injection is also about what is in control of the passing (never the client) and is independent of how the passing is accomplished, whether by passing a reference or a value.

Dependency injection involves four roles:

• the service object(s) to be used
• the client object that is depending on the services it uses
• the interfaces that define how the client may use the services
• the injector, which is responsible for constructing the services and injecting them into the clien

(source)

Dependency injection simply means receiving collaborators as constructor parameters instead of fetching them ourselves. (source)

Reflection is the ability to introspect and reverse engineer functions, classes, methods and interfaces during runtime. This makes it possible to find specific information about your code, such as a classes internal properties, methods & even doc blocks for those methods.

One of my favourite uses for the Reflection API is to have all of my class dependencies automatically injected when possible. If you’re new to dependency injection, then don’t worry, it’s quite simple. This makes my code cleaner to look at, and far more maintainable as the codebase grows. We’ve recently updated our company starter theme/framework to do just this. I figure it’s something I can show you how to do to. The full code & example can be found at the bottom of this post (TL/DR). (source)