dagger2注入不起作用 - SharedPreferences

Question

I am trying my hands on Dependancy Injection using Dagger2 . It gives error in build phase and says cannot inject SharedPreference instance.

Here are my modules and components.

Application Module

@Module
public class ApplicationModule {
    private Application app;
    private String PREF_NAME = "prefs";

    public ApplicationModule(Application app) {
        this.app = app;
    }

    @Singleton
    @Provides
    public Picasso getPicasso() {
        return new Picasso.Builder(app).build();
    }

    @Singleton
    @Provides
    public SharedPreferences getAppPreferences() {
        return app.getSharedPreferences(PREF_NAME, Context.MODE_PRIVATE);
    }
}

ApplicationComponent

@Component(modules = {ApplicationModule.class})
public interface ApplicationComponent {
    void inject(App app);
}

App.java

public class App extends Application {

    ApplicationComponent appComponent;

    @Override
    public void onCreate() {
        super.onCreate();
        createDaggerInjections();
    }

    public ApplicationComponent getAppComponent() {
        return appComponent;
    }

    public static App getAppInstance(Context context) {
        return (App) context.getApplicationContext();
    }

    private void createDaggerInjections() {

        appComponent = DaggerApplicationComponent.builder()
                .applicationModule(new ApplicationModule(this))
                .build();
        appComponent.inject(this);

    }
}

Login Module

@Module
public class LoginModule {

    LoginView view;

    public LoginModule(LoginView view) {
        this.view = view;
    }

    @Provides LoginView getLoginView()
    {
        return view;
    }

    @Provides LoginPresenter getLoginPresenter(LoginView view)
    {
        return new LoginPresenterImpl(view);
    }

}

LoginComponent

@ActivityScope
@Component(
        dependencies = ApplicationComponent.class,
        modules = LoginModule.class)
public interface LoginComponent {
    void inject(LoginActivity activity);

    LoginPresenter getLoginPresenter();
}

LoginActivity.java

public class LoginActivity extends BaseActivity implements LoginView {

    private static final String TAG = "LoginActivity";
    @Inject
    SharedPreferences prefs;
-----
-----
-----
 @Override
    public void createDaggerInjections() {

        DaggerLoginComponent.builder().applicationComponent(App.getAppInstance(this).getAppComponent())
                .loginModule(new LoginModule(this))
                .build();
    }

This line @Inject SharedPreferences prefs; gives error which is as follows. The same error comes when I try to inject Picasso Instance also.

/home/blackidn/proj/styling android 3/dagger 2/DaggerEx/app/src/main/java/com/mohammad/daggerex/App/App.java:8: error: cannot find symbol
import com.mohammad.daggerex.dagger.DaggerApplicationComponent;
                                   ^
  symbol:   class DaggerApplicationComponent
  location: package com.mohammad.daggerex.dagger
/home/blackidn/proj/styling android 3/dagger 2/DaggerEx/app/src/main/java/com/mohammad/daggerex/ui/Login/LoginComponent.java:16: error: android.content.SharedPreferences cannot be provided without an @Provides- or @Produces-annotated method.
    void inject(LoginActivity activity);
         ^
      com.mohammad.daggerex.ui.Login.LoginActivity.prefs
          [injected field of type: android.content.SharedPreferences prefs]

Stucked with this and Don't know how to solve this and move forward. What am I missing ? Any help would be great.

Answer 1

You should expose SharedPreferences to LoginComponent in ApplicationComponent. Otherwise, you can't inject it.

@Component(modules = {ApplicationModule.class})
public interface ApplicationComponent {
    void inject(App app);
    SharedPreferences sharedPreferences();
}

Answer 2

Dagger 2 update : The @Subcomponent could be used without any need to do this as can be seen here for the context: (ChatComponent is a subcomponent with custom scope)

from this excellent article: https://proandroiddev.com/dagger-2-part-ii-custom-scopes-component-dependencies-subcomponents-697c1fa1cfc