Angular 9 應用“NgFor only support binding to Iterables such as Arrays”報錯

Question

我正在使用 Angular 9 開發聯系人應用程序。我通過以下服務獲取聯系人列表：

import { Injectable } from '@angular/core';
import { Observable } from 'rxjs';
import { HttpClient, HttpHeaders } from '@angular/common/http';

import { Contact } from '../models/Contact';

const httpOptions = {
  headers: new HttpHeaders({
    'Content-Type': 'application/json'
  })
}

@Injectable({
  providedIn: 'root'
})

export class ContactsListService {

  contactsUrl = 'https://randomuser.me/api/?&results=500&inc=name,location,email,cell,picture';

  constructor(private http:HttpClient) { }

  getContcts():Observable<Contact[]> {
    return this.http.get<Contact[]>(`${this.contactsUrl}`);
  }

}

聯系人列表組件如下：

import { Component, OnInit } from '@angular/core';
import { from } from 'rxjs';
import { ContactsListService } from '../../services/contacts-list.service';
import { Contact } from '../../models/Contact';

@Component({
  selector: 'app-list',
  templateUrl: './list.component.html',
})

export class ListComponent implements OnInit {

  contactsList:Contact[];

  constructor(private ContactsListService:ContactsListService) { }

  ngOnInit(): void  {
      this.ContactsListService.getContcts().subscribe(contactsList => {
        this.contactsList = contactsList;
      });

  }
}

嘗試以這種方式迭代聯系人列表

<ul *ngFor="let contact of contactsList">
    <li>{{contact.name.first}}</li>
</ul>

拋出錯誤： Cannot find a differ supporting object '[object Object]' of type 'object'. NgFor only supports binding to Iterables such as Arrays Cannot find a differ supporting object '[object Object]' of type 'object'. NgFor only supports binding to Iterables such as Arrays 。

這很可能意味着contactsList不是一個數組。

我究竟做錯了什么？

Answer 1

URL 返回形式為 object

{
  results: [],
  info: {}
}

使用 RxJS map到 map 從 ZDB974238714CA8DE634A7CE1D083A 獲得的results 。

服務

import { Injectable } from '@angular/core';
import { Observable } from 'rxjs';
import { HttpClient, HttpHeaders } from '@angular/common/http';

import { pipe } from 'rxjs';
import { map } from 'rxjs/operators';

import { Contact } from '../models/Contact';

export class ContactsListService {
  contactsUrl = 'https://randomuser.me/api/?&results=500&inc=name,location,email,cell,picture';

  constructor(private http:HttpClient) { }

  getContcts():Observable<Contact[]> {
    return this.http.get<Contact[]>(`${this.contactsUrl}`)
      .pipe(map(response => response['results']));
  }
}

在聲明時將空數組分配給contactsList 。

零件

import { Component, OnInit } from '@angular/core';

import { from } from 'rxjs';

import { ContactsListService } from '../../services/contacts-list.service';
import { Contact } from '../../models/Contact';

@Component({
  selector: 'app-list',
  templateUrl: './list.component.html',
})

export class ListComponent implements OnInit {
  contactsList: Contact[] = []; // assign empty array

  constructor(private ContactsListService:ContactsListService) { }

  ngOnInit(): void  {
    this.ContactsListService.getContcts().subscribe(
      contactsList => { this.contactsList = contactsList; },
      error => { // always good practice to handle error when subscribing to HTTP observables }
    );
  }
}

Answer 2

似乎端點' https://randomuser.me/api/?&results=500&inc=name,location,email,cell,picture '不返回數組。 要檢查它，您可以在瀏覽器中打開它，或者在您的應用運行時檢查 chrome 開發人員工具的網絡選項卡