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Version: 4.2

Fragment Factory

By default, Android creates Fragments with their empty constructor, so you inject them with by inject() (see Android Entry Points). With the AndroidX FragmentFactory, Koin creates the Fragment itself and passes dependencies to its constructor. This page covers the setup, the fragment definition and Fragments from an Activity scope.

The fragment definition is part of io.insert-koin:koin-android. No other artifact is needed.

Setup​

Enable the Koin fragment factory in startKoin:

import org.koin.androidx.fragment.koin.fragmentFactory

startKoin {
    androidContext(this@MainApplication)
    fragmentFactory()
    modules(appModule)
}

Then install it in each Activity that hosts these Fragments, before super.onCreate():

import org.koin.androidx.fragment.android.setupKoinFragmentFactory

class MainActivity : AppCompatActivity() {

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

super.onCreate() restores Fragments after a rotation or process death. The factory must be in place before that, or Android uses the default factory and fails on Fragments without an empty constructor.

Declaring a Fragment​

The Compiler Plugin DSL has no fragment<T>() function. Use the Classic DSL fragment { } or fragmentOf() in the same module:

class UserFragment(private val repository: UserRepository) : Fragment()

val uiModule = module {
    single<UserRepository>()
    fragmentOf(::UserFragment)
}

A fragment definition is a factory: every transaction gets a new Fragment instance. If no definition matches a Fragment class, the Koin factory falls back to the default AndroidX behavior.

Adding a Fragment​

Use the reified replace extension on FragmentTransaction:

import org.koin.androidx.fragment.android.replace

supportFragmentManager.beginTransaction()
    .replace<UserFragment>(R.id.container)
    .commit()

With arguments and a tag:

supportFragmentManager.beginTransaction()
    .replace<UserFragment>(
        containerViewId = R.id.container,
        args = bundleOf("USER_ID" to "42"),
        tag = "user",
    )
    .commit()

Pass per-instance values in args, not in the constructor: Android recreates the Fragment through the factory, and only the arguments are restored.

Fragments from an Activity scope​

To give a Fragment instances from its Activity scope, declare the Fragment inside the scope and pass the scope to setupKoinFragmentFactory():

val checkoutModule = module {
    scope<CheckoutActivity> {
        scopedOf(::CheckoutSession)
        fragmentOf(::PaymentFragment)
    }
}
class CheckoutActivity : ScopeActivity() {

    override fun onCreate(savedInstanceState: Bundle?) {
        setupKoinFragmentFactory(scope)
        super.onCreate(savedInstanceState)
    }
}

With a scope, the factory resolves Fragments from that scope, then from the root scope. In this case it does not need fragmentFactory() in startKoin: that option only declares the global factory used by setupKoinFragmentFactory() without arguments. Activity scopes are covered in Android Scopes.