マルチモジュール時のDagger-AndroidでのInject

AppInjector.kt

import android.app.Activity
import androidx.fragment.app.Fragment
import dagger.android.DispatchingAndroidInjector
import javax.inject.Inject

class AppInjector : HasDispatchingFragmentInjector {

  @Inject
  lateinit var supportFragmentInjector: DispatchingAndroidInjector<Fragment>

  override fun dispatchingFragmentInjector(): DispatchingAndroidInjector<Fragment> = supportFragmentInjector
}

HasDispatchingFragmentInjector.kt

interface HasDispatchingFragmentInjector {
  fun dispatchingFragmentInjector(): DispatchingAndroidInjector<Fragment>
}

ModuleFragmentInjector.kt

import androidx.fragment.app.Fragment
import dagger.android.AndroidInjector

class ModuleFragmentInjector : AndroidInjector<Fragment> {

  private val injectorList = mutableListOf<HasDispatchingFragmentInjector>()

  fun addInjector(injector: HasDispatchingFragmentInjector) {
    injectorList.add(injector)
  }

  override fun inject(instance: Fragment) {
    val wasInjected = injectorList.any { it.dispatchingFragmentInjector().maybeInject(instance) }
    if (!wasInjected) {
      throw IllegalArgumentException("injection failed")
    }
  }
}

MyApplication.kt

class MyApplication : Application(), HasSupportFragmentInjector, HasActivityInjector {

  private val moduleFragmentInjector = ModuleFragmentInjector()

  override fun supportFragmentInjector(): AndroidInjector<Fragment> = moduleFragmentInjector

  override fun onCreate() {
    super.onCreate()

    // OtherModule用のInjectorとComponent作成
    val otherModuleInjector = OtherModuleInjector()
    DaggerOtherModuleComponent.builder()
      ...
      .build()
      .injewct(otherModuleInjector)

    // AppModule用のInjectorとComponent作成
    val appInjector = AppInjector()
    DaggerAppComponent.builder()
      ...
      .inject(appInjector)

    moduleFragmentInjector.addInjector(otherModuleInjector)
    moduleFragmentInjector.addInjector(appInjector)
  }
}

OtherModuleInjector.kt

import android.app.Activity
import androidx.fragment.app.Fragment
import dagger.android.DispatchingAndroidInjector
import javax.inject.Inject

class OtherModuleInjector : HasDispatchingFragmentInjector {

  @Inject
  lateinit var supportFragmentInjector: DispatchingAndroidInjector<Fragment>

  override fun dispatchingFragmentInjector(): DispatchingAndroidInjector<Fragment> = supportFragmentInjector
}