Dagger 2不初始化变量

Question

Now i'm trying to implement dagger in my project, and I have a one problem. Variable that initializes in application component doesn't initialized in my activity. Here is my code. Application:

public class MyApplication extends Application {
    private ApplicationComponent applicationComponent;
    @Inject
    public Context context;

    @Override
    public void onCreate() {
        super.onCreate();
        applicationComponent = DaggerApplicationComponent.builder().applicationModule(new ApplicationModule(this)).build();
        applicationComponent.inject(this);
    }

    public ApplicationComponent getApplicationComponent() {
        return applicationComponent;
    }
}

Here variable context != null

Activity:

public class MainActivity extends AppCompatActivity {
    private ActivityComponent activityComponent;
    @Inject
    Context context;

    @Override
    protected void onStart() {
        super.onStart();
        activityComponent = DaggerActivityComponent.builder()
                .activityModule(new ActivityModule(this))
                .applicationComponent(((MyApplication) getApplication()).getApplicationComponent())
                .build();
        activityComponent.inject(this);
    }
}

Here context == null.

Dagger:

@Component(modules = {ApplicationModule.class})
public interface ApplicationComponent {
    void inject(MyApplication application);
    Context getApplicationContext();
}

@Component(modules = {ActivityModule.class}, dependencies = {ApplicationComponent.class})
public interface ActivityComponent {
    void inject(MainActivity mainActivity);
}

@Module
public class ApplicationModule {
    private Application application;

    public ApplicationModule(MyApplication application) {
        this.application = application;
    }

    @Provides
    Context provideApplicationContext() {
        return application.getApplicationContext();
    }
}

@Module
public class ActivityModule {
    Activity activity;

    public ActivityModule(MainActivity activity) {
        this.activity = activity;
    }
}

So, dagger provide "Context" only in application class, but does not provide it in MainActivity class. What i'm do wrong? May be I have to change something.

Thanks!

Answer 1

Set it up like this:

public class MyApplication extends Application {
  private ApplicationComponent applicationComponent;

  @Override
  public void onCreate() {
    super.onCreate();
    applicationComponent = DaggerApplicationComponent.builder()
            .applicationModule(new ApplicationModule(this))
            .build();
  }

  public ApplicationComponent getApplicationComponent() {
    return applicationComponent;
  }
}

and your activity:

public class MainActivity extends AppCompatActivity {

  @Inject
  Context context;

  @Override
  protected void onStart() {
    super.onStart();
    ((MyApplication) getApplication()).getApplicationComponent().inject(this);
  }
}

Answer 2

This is honestly just a guess, but you should try scoping your components.

@Singleton
@Component(modules = {ApplicationModule.class})
public interface ApplicationComponent {
    void inject(MyApplication application);
    Context getApplicationContext();
}

@Scope
@Retention(RetentionPolicy.RUNTIME)
public @interface ActivityScope {
}

@ActivityScope
@Component(dependencies={ApplicationComponent.class}, modules={ActivityModule.class})
public interface ActivityComponent extends ApplicationComponent {
}