Simple Dependency Injection

this project is inspired by Koin and for learning purposes GDK Jakarta 2019

What is Dependency Injection

In software engineering, dependency injection is a technique whereby one object supplies the dependencies of another object. A "dependency" is an object that can be used, for example as a service. Instead of a client specifying which service it will use, something tells the client what service to use. The "injection" refers to the passing of a dependency (a service) into the 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.

In simple word Dependency Injection is passing dependency to other objects or framework with some techniques.

Why Dependency Injection

• Reusability of code
• Ease of refactoring
• Ease of testing

Basic Type Dependency Injection

Constructor Injection

Dependencies supplied as parameters

class EngineX

data class Plane(private val engine: EngineX)

fun main() {
    val engine = EngineX()

    // Constructor Injection
    Plane(engine)
}

Property Injection

Dependencies injected by accessing properties of object

class EngineX

class Plane {
    lateinit var enginex: EngineX
}

fun main() {
    val enginex = EngineX()
    val plane = Plane()

    //Property Injection
    plane.enginex = enginex
}

Method Injection

Dependencies to be obtained from super class function that implemented by child of super class

interface SuperEngine

class EngineX: SuperEngine

class ShipEngine: SuperEngine

abstract class Vehicle {
    //Method Injection
    private val enginex: SuperEngine = getEngine()

    protected abstract fun getEngine(): SuperEngine
}

class Plane : Vehicle() {
    override fun getEngine(): SuperEngine {
        return EngineX()
    }
}

class Ship : Vehicle() {
    override fun getEngine(): SuperEngine {
        return ShipEngine()
    }
}

Implemented Dependency Injection

• Constructor Injection
• Property Injection

Branch Note

• release-0.2 Injection with qualifier
• release-0.1 The simplest

Library

• Android
• GSON

References

• Google Android Developer Training
• Wikipedia
• Stackoverflow

InjectEngine Documentation

documentation

Log

• add qualifier 3 December 2019
• created 1 December 2019 tobe update