角4从特定的json获取数据

Question

我可以从简单的json获得数据，但是我尝试从一个更复杂的json (对我来说)获得数据，我可以获得初始数据，但是我在获取其余的数据时遇到了困难。My (链接)：

0   
table   "C"
no  "043/C/NBP/2018"
tradingDate "2018-02-28"
effectiveDate   "2018-03-01"
rates   
0   
currency    "dolar amerykański"
code    "USD"
bid 3.3875
ask 3.4559
1   
currency    "dolar australijski"
code    "AUD"
bid 2.6408
ask 2.6942
2   
currency    "dolar kanadyjski"
code    "CAD"
bid 2.6468
ask 2.7002

我可以得到这样的数据，不，tradingDate或effectiveDate，但我不能从利率数据，例如。货币，代码，出价或索要。如何从我的json中获得这些数据？我的服务：

import { Injectable } from '@angular/core';
import { Observable } from 'rxjs/Observable';
import "rxjs/Rx";
import {Npb} from './npb';

import { Http , Response, HttpModule} from '@angular/http';

@Injectable()
export class NbpService {

  private _postsURL = "http://api.nbp.pl/api/exchangerates/tables/c/?format=json";

  constructor(private http: Http) {
  }

  getPosts(): Observable<Npb[]> {
      return this.http
          .get(this._postsURL)
          .map((response: Response) => {
              return <Npb[]>response.json();              
          })         
  }
  private handleError(error: Response) {
      return Observable.throw(error.statusText);
  }
}

构成部分：

import { Component, OnInit } from '@angular/core';
import {NbpService} from './nbp.service';
import {Npb} from './npb';

@Component({
  selector: 'app-home',
  templateUrl: './home.component.html',
  styleUrls: ['./home.component.css'],
  providers: [NbpService]
})
export class HomeComponent implements OnInit {
  _postsArray: Npb[];
  constructor(private NbpService: NbpService, ) {
  }
  getPost(): void {
    this.NbpService.getPosts()
        .subscribe(
            resultArray => this._postsArray= resultArray,
            error => console.log("Error :: " + error)
        )
}

ngOnInit(): void {
    this.getPost();
}
}

和html：

 <tr *ngFor="let post of _postsArray">

    <td>USD</td>
    <td>{{post.effectiveDate}}</td>
    <td>{{post.tradingDate}}</td>
    <td>{{post.ask}}</td>
  </tr>

和Nbp：

export interface Npb {
    date: string;
    buy: string;
    sel: string;
}

Answer 1

你不能像你那样从询问中得到价值。因为ask在速率数组中。您可以执行<td>{{post.rates[0].currency}}</td>，这将为数组的第一个元素提供货币。

如果要打印所有费率，则必须执行另一个循环：

<tr *ngFor='let rate of post.rates'>
  <td>{{rate.currency}}</td>
  <td>{{rate.code}}</td>
  <td>{{rate.bid}}</td>
  <td>{{rate.ask}}</td>
</tr>

Answer 2

当你订阅你收到

[table:..,rates:[{currency:aa,code:bb,}{{currency:aa,code:bb,}..]

那是:一个元素的数组，所以

result[0]={table:..rates:[{...},{...}]}

和

result[0].rates={{...},{...}]

所以

getPosts(): Observable<Npb[]> {
      //See that I use httpClient
      return this.httpClient
          .get(this._postsURL)
          .map((response: any) => {  //see that we received response:any
              return response[0].rates;              
          })         
  }

注意:使用httpClient而不是“旧”http，请参阅https://angular.io/guide/http#httpclient