java - Dagger 2 : inject an interface in a constructor

Question

我正在尝试学习 dagger 2，但我对使用接口(interface)注入(inject)构造函数感到困惑。这是我的以下代码:

MainActivity.java

public class MainActivity extends AppCompatActivity implements MainView {

    // this keyword of request dependency . At compiling process, dagger will look at all of these annotations
    //to create the exact dependency

    @Inject MainPresenter mainPresenter ;
    TextView textView ;


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        textView = findViewById(R.id.textview) ;
        DaggerPresenterComponent.create().inject(this);
        textView.setOnClickListener(new OnClickListener() {
            @Override
            public void onClick(View view) {
                mainPresenter.doThings(8555) ;
            }
        });

    }

    /**********************************/

    @Override
    public void invokeRandomViewMethod(String msg) {
        textView.setText(msg);
    }
}

MainPresenter.java

public class MainPresenter {

    private MainView mainView ;

    @Inject
    public MainPresenter(MainView mainView) {
        this.mainView = mainView;
    }

    public void doThings(int value){
        Random random = new Random();
        int rand= random.nextInt(value) ;
        if(mainView != null){
            mainView.invokeRandomViewMethod("You random number is "+rand);
        }
    }

public interface MainView {
    void invokeRandomViewMethod(String msg) ;
}
}

这是模块:

@Module
public class PresenterModule {

    @Provides
        // this is the method that will provide the dependancy
    MainPresenter provideMainPresenter(MainView mainView){
        return new MainPresenter(mainView);
    }
}

这是组件

@Component (modules = PresenterModule.class)
public interface PresenterComponent {
    void inject(MainActivity activity) ;
}

当我运行代码时，它显示了这个错误:

Error:(15, 10) error: com.imennmn.hellodagger2example.MainView cannot be provided without an @Provides-annotated method. com.imennmn.hellodagger2example.MainView is injected at com.imennmn.hellodagger2example.presenterInjection.PresenterModule.provideMainPresenter(mainView) com.imennmn.hellodagger2example.MainPresenter is injected at com.imennmn.hellodagger2example.MainActivity.mainPresenter com.imennmn.hellodagger2example.MainActivity is injected at com.imennmn.hellodagger2example.simpleInjection.DataComponent.inject(activity)

我的问题是如何通过用 Dagger 注入(inject)接口(interface) MainView 并绑定(bind) MainPresenter 和 MainActivity 来提供接口(interface)？ 任何帮助，将不胜感激 !

Answer 1

通过以下代码:

    MainPresenter provideMainPresenter(MainView mainView) {
        return new MainPresenter(mainView);
    }

你在告诉 dagger:“嘿，每当我要求你注入(inject) MainPresenter 时，请使用 MainView 构建它”。 但是尖锐的提示，因为你没有具体说明他应该如何构建/获取 MainView。

因此，在您的 PresenterModule 中执行此操作:

    @Module
    public class PresenterModule {

        MainView mainView;

        public PresenterModule(MainView mainView) {
            this.mainView = mainView;
        }

        @Provides
        MainPresenter provideMainPresenter() {
            return new MainPresenter(mainView);
        }

    }

然后在构建组件时:

    DaggerPresenterComponent.builder()
                            .presenterModule(new PresenterModule(this))
                            .build();