Can't access property of existing service in component

Question

I have created a service simple service which loads at first a configuration from a JSON file. Because I want that the data is available when the app is started, I'm using the APP_INITIALIZER to load the data.

In the service itself the data is available and everything is fine. But when I use the service from inside a component it gets a strange behaviour. Please can somebody explain whats wrong with my code?

filterService.ts

export class FilterService {
   url:string = '/admin2/src/assets/import.filter.json';
   filters: Filter[];
   currentFilter: Filter;

   public loadFilters() {

      this.http.get(this.url).subscribe(response => {
        this.filters = <Filter[]>response;

        if (this.filters[0])
            this.currentFilter  = this.filters[0];
    });
}

this service is loaded during app init

app.module.ts

 @NgModule({
 ...
 providers: [
    FilterService,
    { provide: APP_INITIALIZER, useFactory: (filterService: FilterService) => () => filterService.loadFilters(), deps: [FilterService], multi: true },
 ],
 ...

Finally, in my component I'm doing:

filter.component.ts

constructor(private filterService: FilterService) {}

ngOnInit() { 
    console.log('import initialized'); 

    console.log(this.filterService);
    console.log(this.filterService.currentFilter);
    console.log(this.filterService.filters);
    console.log(this.filterService.getFilters());
}

And now I really don't understand what is happen in the console.log

  Object { http: {…}, url: "http://...}   // as expected
  undefined                               // ??                               
  undefined                               // ??
  undefined                               // ??

Why can't I access the object properties? It looks to me that everything is fine and available....

Answer 1

In your case =>

app-load.module.ts

import { NgModule, APP_INITIALIZER } from '@angular/core';
import { HttpClientModule } from "@angular/common/http";

import { FilterService } from './filter.service';

export function load_filters(filterService: FilterService) {
    return () => filterService.loadFilters();
}

export function get_filters(filterService: FilterService) {
    return () => filterService.getFilters();
}

@NgModule({
  imports: [HttpClientModule],
  providers: [
    AppLoadService,
    { provide: APP_INITIALIZER, useFactory: load_filters, deps: [FilterService], multi: true },
    { provide: APP_INITIALIZER, useFactory: get_filters, deps: [FilterService], multi: true }
  ]
})
export class AppLoadModule { }

app.module.ts

import { AppLoadModule } from './app-load/app-load.module';
@NgModule({
     imports: [AppLoadModule]
 })

I have followed this blog to create my APP_INITIALIZER => Please read it once(may be useful) https://www.intertech.com/Blog/angular-4-tutorial-run-code-during-app-initialization/