Angular8 http and services missunderstand - angular-services

Question

I'm here because I do not understand how Http works in angular. I would create a "news" thread on my website. To do that I have created a service in my angular app that calls a .net core web API.
Also, I would add a paginate to my thread (I want to display news by 5 on the page).
I can get my values, that is not my issue here. But, to create my paginate, I need to have values for number of pages calculation.
I tried to add code to create my paginate (number of pages, number of elements...) but I always get 0 to these values and my array of news is filled after the onInit(). This is what I don't understand.
This is my component:
import { Component, OnInit, OnDestroy } from '#angular/core';
import { NewsService } from '../news.service';
#Component({
selector: 'app-home',
templateUrl: './home.component.html',
styleUrls: ['./home.component.css']
})
export class HomeComponent implements OnInit {
title = 'News';
news = [];
displayed = [];
numberOfPages = 0;
constructor(private newsService: NewsService) { }
ngOnInit() {
// I don't really understand these lines (mainly the subscribe part)
this.newsService.getAllNews().subscribe((data) => {
this.news = Array.from(Object.keys(data), k => data[k]);
// this console.log appears after the onInit(), why ?
console.log(this.news);
});
this.numberOfPages = this.news.length / 5; // Get 0 here, why ?
}
}
My service:
import { Injectable } from '#angular/core';
import { HttpClient } from '#angular/common/http';
#Injectable({
providedIn: 'root'
})
export class NewsService {
private finalData = [];
private apiUrl = 'https://localhost:5001/api/v1/posts';
constructor(private http: HttpClient) { }
getAllNews() {
return this.http.get(this.apiUrl);
}
}
In the browser console, I get this:
console screen
Maybe I forgot something in my code or I don't know what.
Someone can help me to achieve my goal? I want to understand how to proceed to make a working paginate for my news.

Answer 1

You should add
this.numberOfPages = this.news.length / 5;
inside the subscribe
this.newsService.getAllNews().subscribe((data) => {
this.news = Array.from(Object.keys(data), k => data[k]);
// this console.log appears after the onInit(), why ?
console.log(this.news);
});
like so:
this.newsService.getAllNews().subscribe((data) => {
this.news = Array.from(Object.keys(data), k => data[k]);
// this console.log appears after the onInit(), why ?
console.log(this.news);
this.numberOfPages = this.news.length / 5;
});
My guess is that when you try to initialise the this.numberOfPagesthe this.news.length is not yet set(data are not yet retrieved from the API). Hope this helps