Angular 4 http不返回响应

Question

I have created a simple service to get data via a http request. The data is in json form and I use the map function so that it matches the Blog data type. However when I invoke the method "getBlogs" from the service to get the data nothing is returned. Any thoughts on what I am missing?

The Component.

import {Http} from '@angular/http';
import {forEach} from '@angular/router/src/utils/collection';
import {BlogService} from '../services/blog.service';
import {Component, OnInit} from '@angular/core';
import {Blog} from '../blog/blog';
import {Observable} from 'rxjs/Rx';
import 'rxjs/add/operator/map';
import 'rxjs/Rx';

@Component({selector: 'app-blog-list', templateUrl: './blog-list.component.html',
styleUrls: ['./blog-list.component.css'],
providers: [BlogService]})
export class BlogListComponent implements OnInit {

  blogArray: Blog[] = [];
  blogTitle: string;
  loading: boolean;
  private blogsUrl = 'http://www.mocky.io/v2/59a49eb3100000be05b2aba6';

  constructor(private blogService: BlogService, private http: Http) {}

  ngOnInit() {
    this.blogService
      .getBlogs(this.blogsUrl)
      .subscribe(res => {
        this.blogArray = res;
        console.log('theBlogArray', this.blogArray);
      });
  }

}

The Service

import { Observable } from 'rxjs/Rx';
import 'rxjs/add/operator/map';
import 'rxjs/Rx';
import {Headers, Http } from '@angular/http';
import { Injectable } from '@angular/core';
import {Blog} from '../blog/blog';

@Injectable()
export class BlogService {


  private loading: boolean;
  constructor(private http: Http) {}


  getBlogs(url: string): Observable<Blog[]> {
    this.loading = true;
    return this.http.get(url)
      .map((response) => response.json());
  }

}

As mentioned in the answers it might be a CORS issue. However, I do not get any errors at all in the console. Just in case I enabled the CORS chrome extension (it's called Allow-Control-Allow-Origin: *) on my browser, which is what I usually do when I have CORS issues and I made sure to put it in the header of mocky, again as suggested. Nothing yet, no complain from the console and webpack compiles successfully.

If I hard code the values of the json request into an array in the service an access it via component, the values are returned and I can console.log them and display them on the html.

Answer 1

ngOnInit() {
    this.blogService.getBlogs(this.blogsUrl)
      .subscribe(res => {this.blogArray = res;
console.log('theBlogArray: ', this.blogArray);// this will work and use it in template like{{blogArray}}
);


  }

You are getting the data the only thing is that you are console logging it outside as it is a async call you cannot log in synchronous context.

Update

I tried this same url using angular it is giving some CORS issue there is something wrong with the backend there please check console. you will get error

Answer 2

The console print outside of the subscription will not wait for response.So try like

ngOnInit() {
    this.blogService.getBlogs(this.blogsUrl)
        .subscribe(res => {
           this.blogArray = res;
           console.log('theBlogArray: ', this.blogArray);
    }, Err => console.log(Err));
}

.

// Service   
import 'rxjs/add/operator/catch';

return this.http.get(url)
  .map((response) => response.json())
  .catch(Err);

Answer 3

The reason why I was not seeing the response from the http request was because I was making a reference to the blog-list component inside the main app component without importing blog-list in the main app component.

I was doing this

<app-nav-bar></app-nav-bar>
<app-blog-list></app-blog-list>

Which required me to do this

import { Component } from '@angular/core';
import { BlogListComponent } from './blog-list/blog-list.component';

    @Component({
      selector: 'app-root',
      templateUrl: './app.component.html',
      styleUrls: ['./app.component.css']
    })
    export class AppComponent {
      title = 'app';
    }

I am still unsure why I am able to access the value of the hard coded array from the service and not from the http request without importing blog-list.component into the main app.

blog.service

public blogExample: Blog;
  private loading: boolean;

  constructor(private http: Http) {
    this.blogExample = {
      id: 1,
      title: 'title',
      content: 'content'
    };
  }

blog-list.component

ngOnInit() {
    this.blogService
      .getBlogs(this.blogsUrl)
      .subscribe(res => {
        this.blogArray = res;
        console.log('theBlogArray', this.blogArray);
      });

    console.log('blogExample', this.blogService.blogExample);

  }