Dagger 2注入构造函数的参数 [英] Dagger 2 injecting parameters of constructor

问题描述

我在 Dagger 2网站上看到了以下示例:

I saw the following example on the Dagger 2 website:

class Thermosiphon implements Pump {
  private final Heater heater;

  @Inject
  Thermosiphon(Heater heater) {
    this.heater = heater;
  }

  ...
}

和文档:

当请求一个新实例时，Dagger将获得所需的实例 参数值并调用此构造函数.

When a new instance is requested, Dagger will obtain the required parameters values and invoke this constructor.

当我编写一个模块以提供Thermosiphon之类的

When I write a Module to provide a Thermosiphon like

@Module
public class ThermosiphonModule {

    @Provides
    @Singleton
    Thermosiphon provideThermosiphon() {
        return new Thermosiphon(???);
    }

}

Thermosiphon构造函数仍然需要Heater作为参数，从而使整个自动注入构造函数依赖项"无效.

the Thermosiphon constructor still requires a Heater as an argument, rendering the whole 'automatic injection of constructor dependencies' useless.

我尝试了

return new Thermosiphon(null); 

和

return new Thermosiphon(); 

(空的构造函数)，并希望Dagger2接收到​​我希望注入缺少的Heater的信息，但是提供的Thermosiphon的Heater始终为null；

(empty constructor) and hoped for Dagger2 to pick up that I wanted the missing Heater to be injected, yet the Heater of the provided Thermosiphon is always null;

我验证了我的HeaterComponent/HeaterModule能否正常工作并且能够提供Heater.

I verified though my HeaterComponent / HeaterModule are working fine and are able to provide a Heater.

我是否完全误解了"Dagger满足您对构造函数的依赖性"的全部功能，还是我错过了一些东西?

Do I completey misunderstand the whole feature of 'Dagger satisfies constructor dependencies for you' or am I missing something?

推荐答案

如果您使用的是模块，那么如果您有两个提供程序模块绑定到同一组件，则可以让他们看到加热器作为构造函数参数.

If you're using modules, then if you have two provider modules bound to the same component, then you'll be able to allow them to see the heater as a constructor parameter.

@Module
public class HeaterModule {
    @Provides
    @Singleton
    Heater heater() {
        return new Heater(); // if not using @Inject constructor
    }
}

@Module
public class ThermosiphonModule {
    @Provides
    @Singleton
    Thermosiphon thermosiphon(Heater heater) {
        return new Thermosiphon(heater); // if not using @Inject constructor
    }
}

@Singleton
@Component(modules={ThermosiphonModule.class, HeaterModule.class})
public interface SingletonComponent {
    Thermosiphon thermosiphon();
    Heater heater();

    void inject(Something something);
}

public class CustomApplication extends Application {
    private SingletonComponent singletonComponent;

    @Override
    public void onCreate() {
        super.onCreate();
        this.singletonComponent = DaggerSingletonComponent.builder().build(); //.create();
    }

    public SingletonComponent getSingletonComponent() {
        return singletonComponent;
    }
}

---

但是使用构造函数注入，只要它们具有@Inject构造函数，您还可以提供该给定范围的对象或无作用域的对象.

---

But with constructor injection, you will also be able to provide objects of that given scope, or unscoped objects, as long as they have a @Inject constructor.

例如，

@Singleton
@Component // no modules
public interface SingletonComponent {
    Thermosiphon thermosiphon();
    Heater heater();

    void inject(Something something);
}

还有

@Singleton
public class Heater {
    @Inject
    public Heater() {
    }
}

还有

@Singleton
public class Thermosiphon {
    private Heater heater;

    @Inject
    public Thermosiphon(Heater heater) {
        this.heater = heater;
    }
}

或

@Singleton
public class Thermosiphon {
    @Inject
    Heater heater;

    @Inject
    public Thermosiphon() {
    }
}

这篇关于Dagger 2注入构造函数的参数的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！