dagger-2 Getting started with dagger-2 Android example

Example

One of the central difficulties of writing an Android application using Dagger is that many Android framework classes are instantiated by the OS itself, like Activity and Fragment, but Dagger works best if it can create all the injected objects. Instead, you have to perform members injection in a lifecycle method. Starting from version 2.10 dagger allows using dagger.android which simplify using dagger with android components.

Injecting Activity objects

1. Install AndroidInjectionModule in your application component to ensure that all bindings necessary for these base types are available.

   @Component(modules = {AndroidInjectionModule.class})
   public interface AppComponent {}
   

2. Start off by writing a @Subcomponent that implements [AndroidInjector][AndroidInjector], with a @Subcomponent.Builder that extends [AndroidInjector.Builder][AndroidInjector.Builder]:

   @Subcomponent
   public interface MainActivityComponent extends AndroidInjector<MainActivity> {
       @Subcomponent.Builder
       abstract class Builder extends AndroidInjector.Builder<MainActivity> {}
   }
   

3. After defining the subcomponent, add it to your component hierarchy by defining a module that binds the subcomponent builder and adding it to the component that injects your Application:

   @Module(subcomponents = MainActivityComponent.class)
   public abstract class MainActivityModule {
   
       @Binds @IntoMap @ActivityKey(MainActivity.class)
       abstract AndroidInjector.Factory<? extends Activity>
       bindMainActivityInjectorFactory(MainActivityComponent.Builder builder);
   }
   

4. Next, make your Application implement HasDispatchingActivityInjector and @Inject a DispatchingAndroidInjector<Activity> to return from the activityInjector() method:

   public class MyApp extends Application implements HasDispatchingActivityInjector     {
   
       @Inject
       DispatchingAndroidInjector<Activity> dispatchingActivityInjector;
   
       @Override
       public void onCreate() {
          super.onCreate();
          DaggerAppComponent.create().inject(this);
       }
   
       @Override
       public DispatchingAndroidInjector<Activity> activityInjector() {
           return dispatchingActivityInjector;
       }
   }
   

5. Finally, in your Activity.onCreate() method, call AndroidInjection.inject(this) before calling super.onCreate();:

   public class MainActivity extends Activity {
       public void onCreate(Bundle savedInstanceState) {
           AndroidInjection.inject(this);
           super.onCreate(savedInstanceState);
       }
   }
   

This example was based on official dagger documentation. Working sample can be found on github