Android Entry Points

Note: Examples on this page assume usage of the Gradle plugin. If you are not using the plugin, please read this page for details.

Android types

Once you have enabled members injection in your Application, you can start enabling members injection in your other Android classes using the @AndroidEntryPoint annotation. You can use @AndroidEntryPoint on the following types:

1. Activity
2. Fragment
3. View
4. Service
5. BroadcastReceiver¹

Note that ViewModels are supported via a separate API @HiltViewModel. ContentProviders are not directly supported due to their onCreate being called at startup, but you can access dependencies via an entry point.

The following example shows how to add the annotation to an activity, but the process is the same for other types. When adding to other types, note that as a general rule, Hilt types need to be attached to other Hilt types to work. So before adding [@AndroidEntryPoint] to a fragment, the activity must be annotated as well.

To enable members injection in your activity, annotate your class with @AndroidEntryPoint.

@AndroidEntryPoint
public final class MyActivity extends MyBaseActivity {
  // Bindings in SingletonComponent or ActivityComponent
  @Inject Bar bar;

  @Override
  public void onCreate(Bundle savedInstanceState) {
    // Injection happens in super.onCreate().
    super.onCreate();

    // Do something with bar ...
  }
}

@AndroidEntryPoint
class MyActivity : MyBaseActivity() {
  // Bindings in SingletonComponent or ActivityComponent
  @Inject lateinit var bar: Bar

  override fun onCreate(savedInstanceState: Bundle?) {
    // Injection happens in super.onCreate().
    super.onCreate()

    // Do something with bar ...
  }
}

Note: Hilt currently only supports activities that extend ComponentActivity and fragments that extend androidx library Fragment, not the (now deprecated) Fragment in the Android platform.

Retained Fragments

Calling setRetainInstance(true) in a Fragment’s onCreate method will keep a fragment instance across configuration changes (instead of destroying and recreating it).

A Hilt fragment should never be retained because it holds a reference to the component (responsible for injection), and that component holds references to the previous Activity instance. In addition, scoped bindings and providers that are injected into the fragment can also cause memory leaks if a Hilt fragment is retained. To prevent Hilt fragments from being retained, a runtime exception will be thrown on configuration change if a retained Hilt fragment is detected.

A non-Hilt fragment can be retained, even if attached to a Hilt activity. However, if that fragment contains a Hilt child fragment, a runtime exception will be thrown when a configuration change occurs.

Note: While it’s not recommended, Hilt fragments can be detached and reattached to the same activity instance. In this case, the Hilt fragment will only be injected on the first call to onAttach. Note that this is not the same as retaining a fragment, because a retained fragment will be reattached to a different instance of the activity. Again, this is not recommended, and it is often less confusing to just create a new fragment instance for each usage.

Views with Fragment bindings

By default, only SingletonComponent and ActivityComponent bindings can be injected into the view. To enable fragment bindings in your view, add the @WithFragmentBindings annotation to your class.

@WithFragmentBindings
@AndroidEntryPoint
public final class MyView extends MyBaseView {
  // Bindings in SingletonComponent, ActivityComponent,
  // FragmentComponent, and ViewComponent
  @Inject Bar bar;

  public MyView(Context context, AttributeSet attributeSet) {
    super(context, attributeSet);

    // Do something with bar...
  }

  @Override
  public void onFinishInflate() {
    super.onFinishInflate();

    // Find & assign child views from the inflated hierarchy.
  }
}

@AndroidEntryPoint
@WithFragmentBindings
class MyView : MyBaseView {
  // Bindings in SingletonComponent, ActivityComponent,
  // FragmentComponent, and ViewComponent
  @Inject lateinit var bar: Bar

  constructor(context: Context) : super(context)
  constructor(context: Context, attrs: AttributeSet?) : super(context, attrs)

  init {
    // Do something with bar ...
  }

  override fun onFinishInflate() {
    super.onFinishInflate();

    // Find & assign child views from the inflated hierarchy.
  }
}