Question

对不起我的英语，现在我开始学习dagger2，我不明白为什么我有错误：

错误：（9,10）错误： test.dagger.dagger.modules.MainActivityPresenterModule不能没有@Inject构造函数或@ Provide-或者提供 @ Produces-annotated方法。注入test.dagger.dagger.modules.MainActivityPresenterModule test.dagger.view.activitys.MainActivity.mainActivityPresenterModule test.dagger.view.activitys.MainActivity注入 test.dagger.dagger.components.AppComponent.injectMainActivity（mainActivity）

应用

public class App extends Application {

    private static AppComponent component;

    @Override
    public void onCreate() {
        super.onCreate();
        component = DaggerAppComponent.create();
    }

    public static AppComponent getComponent() {
        return component;
    }

}

AppComponent

@Component(modules = {MainActivityPresenterModule.class})
public interface AppComponent {
    void injectMainActivity(MainActivity mainActivity);
}

MainActivityPresenterModule

@Module
public class MainActivityPresenterModule {

    @Provides
    MainActivityPresenter provideActivityPresenter(NetworkUtils networkUtils) {
        return new MainActivityPresenter(networkUtils);
    }

    @Provides
    NetworkUtils provideNetworkUtils(){
        return new NetworkUtils();
    }


}

NetworkUtils

public class NetworkUtils {

    public boolean isConnection() {
        return true;
    }

}

MainActivityPresenter

public class MainActivityPresenter {

    NetworkUtils networkUtils;

    public MainActivityPresenter(NetworkUtils networkUtils) {
        this.networkUtils = networkUtils;
    }

    public void getUser(){
        if(networkUtils.isConnection()) {
            Log.e("getUser", "getUser");
        } else {
            Log.e("no internet", "no internet connection");
        }
    }

}

MainActivity

public class MainActivity extends AppCompatActivity {


    @Inject
    MainActivityPresenterModule mainActivityPresenterModule;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        App.getComponent().injectMainActivity(MainActivity.this);


    }
}

Answer 1

您只能注入用@Module注释的类中提供的内容（只有该模块中用@Provides注释的方法）。所以，你可以做@Inject MainActivityPresenter presenter，例如，不要尝试注入整个模块，就像你试图做的那样。模块应该在Dagger初始化时注册，就像这样（在App＃onCreate中）

component = DaggerAppComponent.builder()
    .mainActivityPresenterModule(MainActivityPresenterModule())
    .build()

在MainActivity中，您只需调用inject即可注入模块中定义的@Inject MainActivityPresenter presenter或任何其他注入，如下所示：

@Inject MainActivityPresenter presenter    

override fun onCreate(savedInstanceState: Bundle) {
   super.onCreate(savedInstanceState)
   (application as App).component.inject(this)

   // after #inject(this) above you can start using your injections:

   presenter.getUser()
}

抱歉，我在Kotlin编写了代码片段，因为用这种方式编写代码片段要少得多，希望你能够了解它在Java中的外观。

没有构造函数就不能提供Dagger 2

1 个答案: