Basics #3: Scopes and the "tier-like" system

MainActivity.kt

import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import androidx.fragment.app.Fragment
import dagger.hilt.android.AndroidEntryPoint
import dagger.hilt.android.scopes.ActivityScoped
import javax.inject.Inject

@AndroidEntryPoint
class MainActivity : AppCompatActivity() {

    @Inject
    lateinit var someClass: SomeClass

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        println(someClass.doAThing())
    }
}

@AndroidEntryPoint
class MyFragment: Fragment(){

    @Inject
    lateinit var someClass: SomeClass
}


@ActivityScoped
// @FragmentScoped // Try this is will throw compile time error
class SomeClass
@Inject
constructor(

){
    fun doAThing(): String{
        return "Look I did a thing!"
    }
}

scopes.md

https://developer.android.com/training/dependency-injection/hilt-android#component-scopes Most important point to understand here is the "tier-like" system of scoping.

1. @Singleton

• Can inject into anything

2. ActivityRetainedScope

• Inject into everything except Singleton scoped objects
• Ex: Can't inject into Application class

3. ActivityScope

• Inject into everything except Singletonand ActivityRetainedComponent scoped objects
• Ex: Can't inject into Application or ViewModel

4. FragmentScope

• Inject into everything except Singleton, ActivityRetainedComponent andActivityScope` scoped objects
• Ex: Can't inject into Activity, ViewModel or Application

5. I think you get the idea. See the doc link: https://developer.android.com/training/dependency-injection/hilt-android#component-scopes