Dependency Injection with Dagger2

Add the dependencies

dependencies {
    ...

    // Add Dagger dependencies
    compile 'com.google.dagger:dagger:2.12'
    annotationProcessor 'com.google.dagger:dagger-compiler:2.12'
    compile 'com.google.dagger:dagger:' + daggerVersion

    // Using classes in dagger.android
    compile 'com.google.dagger:dagger-android:2.12'
    annotationProcessor 'com.google.dagger:dagger-android-processor:2.12'

    // Using classes in dagger.android with support libraries
    compile 'com.google.dagger:dagger-android-support:2.12'
}

• Fix conflict with dependency

  Error:Conflict with dependency 'com.google.code.findbugs:jsr305' in project ':app'. Resolved versions for app (3.0.1) and test app (2.0.1) differ. See http://g.co/androidstudio/app-test-app-conflict for details.
  

  apply plugin: 'com.android.application'
  
  android {
      ...
  
      configurations.all {
          resolutionStrategy.force 'com.google.code.findbugs:jsr305:3.0.2'
      }
  }
  

InjectingActivityobjects

• Create the application object and its component.

  public class MyApp extends Application {
  
    @Override
    public void onCreate() {
      super.onCreate();
    }
  }
  

  <?xml version="1.0" encoding="utf-8"?>
  <manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.hsy.di">
  
    <application
      android:name=".MyApp"
      android:theme="@style/AppTheme">
      <activity android:name=".MainActivity">
        ...
      </activity>
    </application>
  
  </manifest>
  

  @Component
  public interface MyAppComponent extends AndroidInjector<MyApp> {
  
  }
  

• InstallAndroidInjectionModulein the application component.

  @Component(modules = {AndroidInjectionModule.class})
  public interface MyAppComponent extends AndroidInjector<MyApp> {
  
  }
  

• Define the subcomponent for MainActivity.

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

• Defind a module that binds the subcomponent builder.

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

• Add above module to the component that injects theApplication.

  @Component(modules = {AndroidInjectionModule.class, MainActivityModule.class})
  public interface MyAppComponent extends AndroidInjector<MyApp> {
  
  }
  

• Make theApplicationimplementHasActivityInjector.

  public class MyApp extends Application implements HasActivityInjector {
    @Inject
    DispatchingAndroidInjector<Activity> dispatchingAndroidInjector;
  
    @Override
    public void onCreate() {
      super.onCreate();
      DaggerMyAppComponent.create().inject(this);
    }
  
    @Override
    public AndroidInjector<Activity> activityInjector() {
      return dispatchingAndroidInjector;
    }
  }
  

• CallAndroidInjection.inject(this).

  public class MainActivity extends AppCompatActivity {
  
    @Override
    protected void onCreate(Bundle savedInstanceState) {
      AndroidInjection.inject(this);
      super.onCreate(savedInstanceState);
      setContentView(R.layout.activity_main);
    }
  }
  

• Select Build > Make Project to trigger the generation of the code. Then DaggerMyAppComponent will be find.

Dagger & Android

Using Dagger 2 for dependency injection in Android - Tutorial