Dagger 2：在构造函数中注入接口

Question

我正在尝试学习 dagger 2，但我对使用接口注入构造函数感到困惑。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，它向我显示此错误：

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注入 Dagger 并绑定 MainPresenter 和 MainActivity 来提供接口 MainView ？任何帮助，将不胜感激！

Answer 1

您的 provideMainPresenter 隐含地依赖于 MainView。匕首没有办法得到它。您需要添加一个方法来提供它：

@Module
public class PresenterModule {

    @Provides
    MainView provideMainView(){
        // Provide MainView here somehow so Dagger can use this to create a MainPresenter
    }

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

Answer 2

通过以下代码：


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

你在告诉匕首："hey, whenever I ask you to inject MainPresenter, construct it using MainView"。但是匕首投诉，因为你还没有具体说明他应该如何 build/acquire 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();

Answer 3

添加带有@Binds注解的抽象模块，看我的实现：AbstractTestSettingsFragmentModule.java

TestFragment.java

public class TestFragment extends Fragment{

    @Inject TestFragmentContract.Presenter mPresenter;

    @Override
    public void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        AndroidSupportInjection.inject(this);

    }

 }

TestFragmentPresenterImpl.java

public class TestFragmentPresenterImpl implements TestFragmentContract.Presenter {

    @Inject
    public TestFragmentPresenterImpl(){
    }
}

AbstractTestSettingsFragmentModule.java

@Module
public abstract class AbstractTestSettingsFragmentModule {

    @Binds
    @NonNull
    public abstract TestSettingsFragmentContract.Presenter testSettingsFragmentPresenterImpl(TestSettingsFragmentImpl presenter);

}

ContributesModule.java

   @Module
    public abstract class ContributesModule {

        @ContributesAndroidInjector(modules = {AbstractTestSettingsFragmentModule.class})
        abstract TestSettingsFragment testSettingsFragment();
    }

AppComponent.java

@Singleton
@Component(
        modules = {
                AndroidSupportInjectionModule.class,
                ContributesModule.class,
                AppModule.class,
              })
public interface AppComponent extends AndroidInjector<DaggerApplication> {

    void inject(TheApplication theApplication);

    @Override
    void inject(DaggerApplication instance);

    @Component.Builder
    interface Builder {

        @BindsInstance
        Builder application(Application application);

        AppComponent build();

    }

}

Dagger 2：在构造函数中注入接口

Dagger 2: inject an interface in a constructor

java

android

dependency-injection

dagger

dagger-2