Send data from service to observable Get request

Question

I am new to Angular and Observables. I have a service that receives a URL I want to pass to my observable and render data every time a new URL is passed to it with NgFor. Any example would help. Please help nothing seems to work. Thanks in advance

SERVICE File

import { Injectable } from '@angular/core';
import { HttpClient, HttpErrorResponse, HttpHeaders, HttpParams } from '@angular/common/http';
import { Observable } from 'rxjs';
import { Event } from '../event/event.interface';
import { map } from 'rxjs/operators';

@Injectable({
  providedIn: 'root'
})

export class ClientService {

  eventUrl ;

  constructor(private http: HttpClient) {
  }

 receiveEvent(eventId){
    this.eventUrl = eventId;
   console.log(this.eventUrl)
 }

renderEvent(eventUrl): Observable<Event[]>{
  return this.http
  .get<Event[]>(eventUrl)
}

RECEIVING COMPONENT file

import { Component, OnInit, Input, Output, EventEmitter } from '@angular/core';
import { ClientService } from '../service/clientService';
import { HttpParams, HttpClient } from '@angular/common/http';


@Component({
  selector: 'hero-review',
  templateUrl: './review.component.html',
  styleUrls: ['./review.component.css']
})
export class ReviewComponent implements OnInit {

public events = [];

  constructor(private _clientService: ClientService) { 
  }

  ngOnInit() {

    this._clientService.renderEvent('Need to be dynamic URL').subscribe(data => this.events = data);
  }
}

SENDING COMPONENT file

sendEvent(eventId){
  let reqUrl = "myEndpoint" + eventId;
  this._clientService.receiveEvent(reqUrl);
}

Answer 1

// This sample using angular 9/10
// Component name:  list.component.ts

import { HttpClient } from '@angular/common/http';
import { Component, OnInit } from '@angular/core';
import { NgZone} from '@angular/core';
import {HttpServiceService} from './../http-service.service';

@Component({
  selector: 'app-list',
  templateUrl: './list.component.html',
  styleUrls: ['./list.component.scss']
})
export class ListComponent implements OnInit {

  constructor(
     private http: HttpServiceService,
     private zone: NgZone
    ) { }
  brews: object;
  ngOnInit(): void {
      this.http.getPeople().subscribe(data => {
      this.brews = data;
      alert(JSON.stringify(this.brews));
      console.log(this.brews);
      });
  }
}
//--------------------------------

// This is my http service
// Component Name: http-service.service.ts

import { Observable, of } from 'rxjs';
import { Injectable } from '@angular/core';

@Injectable({
  providedIn: 'root'
})
export class HttpServiceService {

  constructor() { }
  getPeople(): Observable<any>{
    const myNameArray = [{
      firstName: 'Algem',
      lastName: 'Mojedo',
      age: 63
    }];
    return of(myNameArray);
 }
}

//--------------------------
// should display in alert

localhost:4200 says
[{"firstName":"Algem","lastName":"Mojedo","age":"60"}]

Happy coding..

Answer 2

I think I understand your problem.

The http.get(url) is a single-use observable. It's not a stream that can be triggered multiple times like subjects can. You will need to create your own subject and use that as a proxy.

export class ClientService {

 constructor(private http: HttpClient) {
 }

 private eventPublisher: Subject<Event[]> = new Subject<Event[]>();

 receiveEvent(eventId){
   // call http client here, and publish results to event publisher
   const eventUrl = eventId;
   this.http.get<Event[]>(eventUrl).subscribe(response => {
     this.eventPublisher.next(response);
   });
 }

 renderEvent(eventUrl): Observable<Event[]>{
  // do not subscribe to http client here, subscribe to event publisher
  return this.eventPublisher.asObservable();
 }

This is the pub-sub design pattern (publisher - subscriber). It might be useful to read up on other solutions to this design pattern using Angular, as this is a fairly trivial example.

Edit:

You will also want to unsubscribe in your component once you're done with the subscription to avoid memory leaks.

Something like this is a simple pattern:

export class MyComponent implements OnInit, OnDestroy() {
  constructor(private myService: MyService) { }

  private destroyed: Subject<void> = new Subject<void>();

  ngOnInit(): void {
    this.myService.myMethod().pipe(
      takeUntil(() => this.destroyed)
    ).subscribe(() => { 
      // do stuff
    });
  }

  ngOnDestroy(): void {
    this.destroyed.next(undefined);
    this.destroyed.complete();
  }
}

Although it does get repetitive if you need to start doing it a lot. I personally use this method: https://stackoverflow.com/a/45709120/5367916