Dagger ‐ Field injection

Contents
Observations
Output
Code

Observations

• You can clearly see there are three implementations(Wheels, Engine, and Car).

// Dagger generates the component from it we can build the component 
val mobileComponent = DaggerMobileComponent.builder().build()
// Here we pass the context of the activity since we need the context for field injection for dagger
mobileComponent.inject(this@DaggerConceptsActivity)
// Access the methods of the class from the field injected variable
mobile.runMobile()

Output

Battery constructor is invoked !
Screen constructor is invoked !
Mobile constructor is invoked !
Mobile is running !

Code

implementations

Battery.kt

class Battery @Inject constructor() {

    init {
        printLog("Battery constructor is invoked !")
    }

}

Screen.kt

class Screen @Inject constructor(){

    init {
        printLog("Screen constructor is invoked !")
    }

}

Mobile.kt

class Mobile @Inject constructor( var battery: Battery, var screen: Screen){

    init { printLog("Mobile constructor is invoked !") }

    fun runMobile() { printLog("Mobile is running !") }

}

Components

MobileComponent.kt

@Component
interface MobileComponent {

    fun inject(activity: MyActivity)

}

Activities

MyActivity.kt class MyActivity : AppCompatActivity() {

private lateinit var binding: ActivityDaggerConceptsBinding

@Inject
lateinit var mobile : Mobile

override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    binding = ActivityDaggerConceptsBinding.inflate(layoutInflater)
    setContentView(binding.root)
    setOnClickListener()
}

private fun setOnClickListener() {
    binding.apply {
        // Field Injection
        fieldInjectionId.setOnClickListener {
            val mobileComponent = MyActivity.builder().build()
            mobileComponent.inject(this@MyActivity)
            mobile.runMobile()
        }
    }
}

}