如何使用依赖注入扩展组件? [英] How to extend a component with dependency injection?

问题描述

我有以下课程ModuleWithHttp:

@Injectable()
export default class {
  constructor(private fetchApi: FetchApi) {}
}

我想按如下方式使用它:

and I want to use it as follows:

@Component({
  selector: 'main',
  providers: [FetchApi]
})
export default class extends ModuleWithHttp {
  onInit() {
    this.fetchApi.call();
  }
}

因此，通过扩展已经注入依赖项的超类，我想在其子级中对其进行访问.

So by extending a super class that already injects a dependency I want to have an access to it in its children.

我尝试了许多不同的方法，甚至将超类作为组件:

I tried many different ways, even having super-class as a component:

@Component({
  providers: [FetchApi]
})
export default class {
  constructor(private fetchApi: FetchApi) {}
}

但是，即使在超类中，this.fetchApi仍然是null.

But still, this.fetchApi is null, even in super-class.

推荐答案

您必须在超级类中注入fetchAPI并将其传递给子类

You have to inject fetchAPI in the super class and pass it down to the child class

export default class extends ModuleWithHttp {

  constructor(fetchApi: FetchApi) {
     super(fetchApi);
  }   

  onInit() {
    this.fetchApi.call();
  }
}

这是DI一般如何工作的功能.超类将通过继承实例化子级，但是您必须向子级提供必需的参数.

This is a feature of how DI works in general. The super class will instantiate the child via inheritance, but you have to supply the required parameters to the child.

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