Dagger 2 cheatsheet

ActivitiesModule.kt

@Module
abstract class ActivitiesModule {

  @ContributesAndroidInjector(modules = [MainActivityModule::class])
  abstract fun contributeMainActivity(): MainActivity

  // Other activities come here, same as above.
}

app > build.gradle

dependencies {

    // Dagger 2
    implementation 'com.google.dagger:dagger:2.22.1'
    kapt 'com.google.dagger:dagger-compiler:2.22.1'
    implementation 'com.google.dagger:dagger-android:2.22.1'
    implementation 'com.google.dagger:dagger-android-support:2.22.1'
    kapt 'com.google.dagger:dagger-android-processor:2.22.1'

}

ApplicationComponent.kt

@Component(
  modules = [
    AndroidSupportInjectionModule::class,
    ActivitiesModule::class,
    FragmentsModule::class
    // Other modules here.
  ]
)
@Singleton
interface ApplicationComponent : AndroidInjector<MyApplication> {

  interface Factory : AndroidInjector.Factory<MyApplication>
}

FragmentsModule.kt

@Module
abstract class FragmentsModule {

  @ContributesAndroidInjector(modules = [MyFragmentModule::class])
  abstract fun contributeMyFragment(): MyFragment

  // Other fragments come here, same as above
}

MyApplication.kt

class MyApplication : DaggerApplication() {

  override fun applicationInjector(): AndroidInjector<out DaggerApplication> {
    return DaggerApplicationComponent.builder().build()
  }

}

MyFragmentModule.kt

@Module
class MyFragmentModule {

  @Suppress("UNCHECKED_CAST")
  @Provides
  fun provideMyViewModel(fragment: MyFragment, provider: Provider<MyViewModelImpl>): MyViewModel {
    return ViewModelProviders.of(fragment, object : ViewModelProvider.Factory {
      override fun <T : ViewModel?> create(modelClass: Class<T>): T = provider.get() as T
    }).get(MyViewModelImpl::class.java)
  }

  // Other @Provides functions here.
}

MyViewModel.kt

interface MyViewModel {
  // Stuff needed by the UI.
}

class MyViewModelImpl @Inject constructor(private val dependency: Dependency): ViewModel(), MyViewModel {
  // ViewModel related stuff. (LiveData, etc)
}