如何使用构造函数注入创建对象？ [英] How to create an object using constructor injection?

问题描述

我将如何使用提供Cat的组件创建Dog实例。

How would I create an instance of Dog with a component which provides Cat.

public final class Dog {
    private final Cat mCat;
    public final static String TAG = "Dog";

    @Inject public Dog(Cat cat) {
        mCat = cat;
        Log.e(TAG, "Dog class created");
    }
}

尝试使用Dagger 2一段时间后，我没有

After experimenting with Dagger 2 for a while I have no idea how to use constructor injection – a hint would be nice, thanks.

编辑：

，请问如何使用构造函数注入的想法。题？使用Dagger 2之后，按照一些教程并阅读了官方文档后，我不知道如何使用构造函数注入功能，这就是为什么我在这里问。不用使用@Inject将Cat依赖项注入Dog，我可以编写一个提供Dog对象的DogModule，但是Dog只是一个普通的Java类。字段注入效果很好（有很多示例说明了如何使用它），但是使用构造函数注入需要做什么？

Whats wrong with the question? After using Dagger 2, following several tutorials and reading the official documentation I have no clue how to use the constructor injection feature, that's why I ask here. Instead of injecting the Cat dependency into Dog with @Inject I could write a DogModule providing a Dog object, but then Dog would be just a regular Java class. Field injection works great (there are a lot of examples showing how to use it) but what do I need to do to use constructor injection?

推荐答案

要使用Dagger 2构造函数注入功能创建对象，您需要向提供Cat类的组件添加方法。

To create an object using the Dagger 2 constructor injection feature you need to add a method to a component which provides a Cat class.

@Component(
    dependencies = ApplicationComponent.class,
    modules = CatModule.class)
public interface ActivityComponent {
    void inject(final CatActivity a);
    // objects exposed to sub-components
    Cat cat();
    Dog dog();
}

然后可以通过调用来检索Dog的实例[Component] .dog（）。

final ActivityComponent comp = DaggerActivityComponent.builder()
            .applicationComponent(app.getApplicationComponent())
            .build();

final Dog d = comp.dog();

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