How to inject a fragment/activity? (circular dependency)

[afjoseph]

Hey!

This is not your typical situation but please humour me :)

How can an activity/application/fragment be injected as a dependency?

Assuming I have a class AudioPlayer:

class AudioPlayer(private val context: Activity) {
    fun doToast() {
        Toast.makeText(context, "Running Audio player...", Toast.LENGTH_SHORT).show()
    }
}

Which I'll need to inject inside MainActivity:

class MainActivity : BaseActivity() {
    override val contextName = "MainActivity"

    val audioPlayer by inject<AudioPlayer>()

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

        audioPlayer.doToast()
    }
}

How would I provide MainActivity as a dependency for AudioPlayer?

Here is the app module class:

fun appModules() = listOf(applicationModule())

class applicationModule : AndroidModule() {
    override fun context() = applicationContext {
        context(name = "MainActivity") {
            provide { AudioPlayer(get()) }
        }
}

[arnaudgiuliani]

Hello @obaied

your are here in a circular dependency situation. The best way to handle it by property or a function and not directly by constructor. Bind MainActivity <-> AudioPlayer in 2 times.

I propose you something like:

add the contextproperty

class AudioPlayer() {
    lateinit var context: Activity
    fun doToast() {
        Toast.makeText(context, "Running Audio player...", Toast.LENGTH_SHORT).show()
    }
}

bind lately this contextproperty

class MainActivity : BaseActivity() {
    override val contextName = "MainActivity"

    val audioPlayer by inject<AudioPlayer>()

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_layout)
        audioPlayer.context = this
        audioPlayer.doToast()
    }
}

no need to inject context in constructor

fun appModules() = listOf(applicationModule())

class applicationModule : AndroidModule() {
    override fun context() = applicationContext {
        context(name = "MainActivity") {
            provide { AudioPlayer() }
        }
}

Other point: if you audio player just need a context, you can inject the androidContext directly.

[afjoseph]

Got it! Thanks @arnaudgiuliani. I was just trying to see if Koin can automatically inject custom Android components (like Dagger).
Great, great library. I'm making my new app with it!

Cheers!

[arnaudgiuliani]

Nice 👍