如何使用@Inject 并获取不在构造函数中的服务实例？

Question

我有一个在其中使用 http 的通用类：

export abstract class GenericCrudService<T> {
  constructor(protected http: HttpService, protected resourse: Resourse) {}

  private entities: T[] = [];
  entitiesChanged$: Subject<T[]> = new Subject();

  getAllEntities() {
    this.http.get<T>(environment.endpoint + this.resourse).subscribe((res) => {
      this.entities = res;
      this.entitiesChanged$.next(this.entities);
    });
  }

  createEntity(entity: T) {
    return this.http
      .post(environment.endpoint + this.resourse, entity)
      .subscribe((_) => {
        this.entities.push(entity);
        this.entitiesChanged$.next(this.entities);
      });
  }
  deleteEntity(id: string) {
    return this.http
      .delete(environment.endpoint + this.resourse, id)
      .subscribe((res: any) => {
        this.entities = this.entities.filter((e: any) => e._id !== res.deleted);
        this.entitiesChanged$.next(this.entities);
      });
  }

  updateEntity(id: string, newEntity: T) {
    return this.http
      .put(environment.endpoint + this.resourse, id, newEntity)
      .subscribe((res: any) => {
        const updatedIndex = this.entities.findIndex(
          (e: any) => e._id === res.updated
        );
        this.entities[updatedIndex] = newEntity;
        this.entitiesChanged$.next(this.entities);
      });
  }

  getLatestEntities() {
    return this.entitiesChanged$.asObservable();
  }
}

还有扩展该类的服务：

@Injectable({
  providedIn: "root",
})
export class ExerciseService extends GenericCrudService<IExercise> {
  constructor(http: HttpService) {
    super(http, Resourse.exercise);
  }
}

我认为最好不要在练习服务中注入 http 客户端，因为它不需要它，并且只通过执行以下操作在通用客户端中创建它：

@Inject(HTTP_TOKEN?) http : HttpService 并在服务的任何地方使用 this.http。我的问题是，是否有可能并被推荐，如果可以，我怎样才能获得 HttpService 注入令牌，或者如果它不存在，我该如何创建一个？

Answer 1

只有一种“优雅”的方式可以在 Angular 中注入任何东西，那就是构造方法。另一种方法是在构造函数中注入 Injector 并在运行时的任何时刻注入 Injector.get(token)。

myService = this.injector.get(MyService);
constructor(private injector: Injector) {}

在你的代码中

export abstract class GenericCrudService<T> {
  protected http = this.injector.get(HttpService);
  constructor(protected injector: Injector, protected resourse: Resourse) {}
...
}
....
export class ExerciseService extends GenericCrudService<IExercise> {
  constructor(injector: Injector) {
    super(injector, Resourse.exercise);
  }
}

那么在任何后代中，您只会将注入器传递给父级，并且父级可以在此注入器的帮助下注入任何它想要的东西