How can I use a service to initialize a variable once on app.module and use it later in other components?

Thieb

I have to generate a list of objects once the app starts using the service from the backend API, the question is how to initialize the list with other components and access it?

For example, in app.module.ts I want something like:

    export class AppComponent {
  title = 'General Title';
  myListFromServiceApi:[DataType]; 
  }

How to call it in mycomponent.ts

ngOnInit() {
this.myListFromServiceApi= ??
}

edit

I already have the service, but I want to avoid calling the service every time a component is added to the view, i.e. once in the life of the application if possible, how can I achieve this?

Jan Wendland

You can use the rx operator to prevent multiple executions of side effects (http requests in your case) when subscribing to multiple subscribers, and return an observable that is piped from the service , ie :shareshareDataTypeService

export class DataTypeService {

  dataTypes$: Observable<DataType>;

  constructor(private http: HttpClient) {
    this.dataTypes$ = this.http.get('/api/datatypes').pipe(share());
  }

  getDataTypes() {
    return this.dataTypes$;
  }
}

In your component you can inject DataTypeService, subscribe to the returned observable getDataTypes()and the request will only be executed once.

constructor(private dataTypeService: DataTypeService){
   this.dataTypeService.getDataTypes().subscribe(dataTypes => {
       this.myListFromServiceApi = dataTypes;
   })
}

If you only want to use these data types in templates, you can also store the returned observable directly getDataTypes()on the component and take advantage of the pipelineasync

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