When using Angular, a service can be declared in the viewProviders of the parent component and then accessed in the viewProviders of the child

Question

When using Angular, a service can be declared in the viewProviders of the parent component and then accessed in the viewProviders of the child

Imagine a scenario where there is a parent component called AppComponent, a directive named MyDirective, and a service named SimpleService.

In this case, MyDirective is utilized in the template of AppComponent and injects SimpleService using the Host decorator. To avoid using the instance from the parent of AppComponent, a new instance is created within the viewProviders of AppComponent.

However, a situation arises with the introduction of a child component called HelloComponent under AppComponent. Now, HelloComponent also uses MyDirective, but in this case, I want the MyDirective inside HelloComponent to utilize the same instance of SimpleService from AppComponent. How can this be achieved?

I attempted utilizing

{provide: SimpleService, useExisting: SimpleService}

, but it resulted in a cyclic dependency error.

Sample code: https://stackblitz.com/edit/angular-7h352z?file=src%2Fapp%2Fhello.component.ts

angular typescript web-frontend

Answer 1

Answer №1

To implement this as a singleton service, all you need to do is apply the following decorator to your code:

@Injectable({
  providedIn: 'root',
})

By adding this code snippet, you will ensure that there is only one instance of this service created and shared throughout your application.

Answer 2

To implement this as a singleton service, all you need to do is apply the following decorator to your code:

@Injectable({
  providedIn: 'root',
})

By adding this code snippet, you will ensure that there is only one instance of this service created and shared throughout your application.

Answer 3

Answer №2

Utilize the providers property to make a provider accessible to both its content children and view children.

Give this a shot:

providers: [{provide: NewService, useValue: NewService }]

See Example

Answer 4

Utilize the providers property to make a provider accessible to both its content children and view children.

Give this a shot:

providers: [{provide: NewService, useValue: NewService }]

See Example

Answer 5

Answer №3

Utilize the @SkipSelf() decorator in the constructor

@Component({
  selector: 'hello',
  template: `child <input myDirective >{{value}}`,
  styles: [`h1 { font-family: Lato; }`],
  viewProviders: [SimpleService]

})
export class HelloComponent implements OnInit  {
  constructor(@Host() @Optional() @SkipSelf() private simpleService: SimpleService) {}
  value:any
  ngOnInit()
  {
    this.value=this.simpleService?this.simpleService.message:"No service"
  }
}

Please note that if you need both services, you can inject the own service as follows:

constructor(
     @Host() @Optional() @SkipSelf() private simpleService: SimpleService
     private simpleServiceChild:SimpleService
   ) {}

Answer 6

Utilize the @SkipSelf() decorator in the constructor

@Component({
  selector: 'hello',
  template: `child <input myDirective >{{value}}`,
  styles: [`h1 { font-family: Lato; }`],
  viewProviders: [SimpleService]

})
export class HelloComponent implements OnInit  {
  constructor(@Host() @Optional() @SkipSelf() private simpleService: SimpleService) {}
  value:any
  ngOnInit()
  {
    this.value=this.simpleService?this.simpleService.message:"No service"
  }
}

Please note that if you need both services, you can inject the own service as follows:

constructor(
     @Host() @Optional() @SkipSelf() private simpleService: SimpleService
     private simpleServiceChild:SimpleService
   ) {}

When using Angular, a service can be declared in the viewProviders of the parent component and then accessed in the viewProviders of the child

Answer №1

Answer №2

Answer №3

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