angular 2 injection not work in inheritance

问题

recently we upgraded from Angular 2.0 to 2.4 and since then we have problems with inheritance. all dependencies gets undefined if we call the child.

the child don't have a constructor, what means it uses the father constructor.

this is the code:

@Injectable()
export class ChildComponent extends ParentComponent {

}


export class ParentComponent implements OnInit, AfterViewInit, AfterViewChecked {

    constructor(protected _activitySettingsControlService: ActivitySettingsControlService,
                protected _changeDetectionRef: ChangeDetectorRef,
                protected _elemRef: ElementRef,
                protected _apiService: ApiService) {

    }

all dependencies are undefind in this way.

what can be the reason ?

回答1:

Without a complete example, we can only guess. Consider using the below as a starting point for the requested minimal, complete and verifiable example.

Code sample showing component inheritance and service injection working together:

import { Component, Injectable } from '@angular/core';

@Injectable()
export class SomeDependency {
  public foo() {
    return 'bar';
  }
}

@Component({
  selector: 'parent-comp',
  template: `<h1>Hello from ParentComponent {{name}}</h1>`,
  providers: [
    SomeDependency
  ]
})
export class ParentComponent { 
  public name;
  constructor(private dep: SomeDependency) {
    this.name = this.dep.foo();
  }
}

@Component({
  selector: 'child-comp',
  template: `<h1>Hello from ChildComponent. SomeDependency returned {{name}}</h1>`,
  providers: [
    SomeDependency
  ]
})
export class ChildComponent extends ParentComponent { 

}


@Component({
  selector: 'my-app',
  template: `<child-comp></child-comp>`
})
export class AppComponent { 

}

See this plunker for a working example: http://embed.plnkr.co/5VNDF6/

I am (also) new to supplying examples in SO, so I might have missed some best practices. Hopefully people will comment on suggestions for improvements.

Of general note, this component inheritance is imho not the best way of doing things - I'd favor composition over inheritance for components. Inheritance - if really required - could be a better fit for services: http://embed.plnkr.co/jWiOTg/

来源：https://stackoverflow.com/questions/41789601/angular-2-injection-not-work-in-inheritance

标签

angular

dependencies