GenericController.ts

import {OnDestroy, OnInit} from '@angular/core';
import {BehaviorSubject, Observable, Subject, Subscription} from 'rxjs';
import {filter, takeUntil} from 'rxjs/operators';

export class GenericController implements OnDestroy, OnInit {

  private unsubscribe$ = new Subject<void>();

  isLoadingAsync: Observable<boolean>;
  /* Is loading */
  private isLoadingAsyncSubject = new BehaviorSubject(false);
  private isLoadingBasicDataSubject = new BehaviorSubject(null);
  private isLoadingBasicData: Observable<void>;

  unsubscribeOnDestroy = <T>(value: Observable<T>): Observable<T> => value.pipe(takeUntil(this.unsubscribe$));

  constructor() {
    this.isLoadingAsync = this.isLoadingAsyncSubject.asObservable();
    this.isLoadingBasicData = this.isLoadingBasicDataSubject.asObservable().pipe(filter(data => data != null && !data));
  }

  get isLoading(): boolean {
    return this.isLoadingAsyncSubject.value;
  }

  set isLoading(value: boolean) {
    this.isLoadingAsyncSubject.next(value);
  }

  ngOnInit(): void {
    this.isLoading = true;
    const result = this.loadBasicData();
    this.isLoadingBasicDataSubject.next(true);
    if (result) {
      result.add(() => {
        this.isLoadingBasicDataSubject.next(false);
        this.isLoading = false;
      });
    } else {
      this.isLoadingBasicDataSubject.next(false);
      this.isLoading = false;
    }
  }

  ngOnDestroy() {
    this.isLoadingBasicDataSubject.complete();
    this.isLoadingAsyncSubject.complete();
    this.unsubscribe$.next();
    this.unsubscribe$.complete();
  }

  loadBasicData(): Subscription {
    return null;
  }

  onLoadData(): Observable<void> {
    return this.isLoadingBasicData;
  }

}