Question

在我的Angular 2项目中，ListingService无法通过post从服务器获取数据。我收到了这个错误：

EXCEPTION: TypeError: Cannot read property 'post' of undefined in [null]
ORIGINAL EXCEPTION: TypeError: Cannot read property 'post' of undefined
ORIGINAL STACKTRACE:
TypeError: Cannot read property 'post' of undefined
at ListingService.getListings (http://localhost:3000/app/listing.service.js:30:30)
at ListingsComponent.getListings (http://localhost:3000/app/listings.component.js:45:41)
at ListingsComponent.ngOnInit (http://localhost:3000/app/listings.component.js:41:26)
at AbstractChangeDetector.ChangeDetector_HostListingsComponent_0.detectChangesInRecordsInternal (eval at <anonymous> (http://localhost:3000/node_modules/angular2/bundles/angular2.dev.js:10897:14), <anonymous>:22:99)
at AbstractChangeDetector.detectChangesInRecords (http://localhost:3000/node_modules/angular2/bundles/angular2.dev.js:8824:14)
at AbstractChangeDetector.runDetectChanges (http://localhost:3000/node_modules/angular2/bundles/angular2.dev.js:8807:12)
at AbstractChangeDetector._detectChangesContentChildren (http://localhost:3000/node_modules/angular2/bundles/angular2.dev.js:8871:14)
at AbstractChangeDetector.runDetectChanges (http://localhost:3000/node_modules/angular2/bundles/angular2.dev.js:8808:12)
at AbstractChangeDetector._detectChangesInViewChildren (http://localhost:3000/node_modules/angular2/bundles/angular2.dev.js:8877:14)
at AbstractChangeDetector.runDetectChanges (http://localhost:3000/node_modules/angular2/bundles/angular2.dev.js:8811:12)

我的ListingService.ts看起来像这样：

import {Injectable, Injector} from 'angular2/core';
import {HTTP_PROVIDERS, Http, Headers} from 'angular2/http';
import {Listing} from './listing';
import 'rxjs/add/operator/map';
@Injectable()
export class ListingService {
 http: Http;
 listings: Array<Listing>;
 getListings() {
    var headers = new Headers();
    headers.append('Content-Type', 'application/json');
    this.http.post('http://144.376.29.134:and-so-on', JSON.stringify(
    {"id":1, "title": "Title", "description": "Проводите", "discount": "21%", "imageUrl": "http://lorempixel.com/400/200/sports", "tags": [{"tag": "Еда"}]
    }),{headers:headers}
    ).map(res => res.json())
    .subscribe((res:Array<Listing>) => this.listings = res);
    return Promise.resolve(this.listings);
 }
 getListing(id: number) {
    return Promise.resolve(this.listings)
    .then(listings => listings.filter(l => l.id === id)[0]);
 }
}

使用ListingService的ListingsComponent看起来像这样：

import {Component, OnInit} from 'angular2/core';
import {HTTP_PROVIDERS, Http, Headers} from 'angular2/http';
import {Listing} from './listing';
import {ListingService} from './listing.service';
import 'rxjs/add/operator/map';
@Component({
  ....
})
export class ListingsComponent implements OnInit {
 listings: Array<Listing>;
 constructor(private listingService:ListingService, private _router: Router) {}
 ngOnInit() {
  this.getListings();
 }
 getListings() {
  this.listingService.getListings().then(listings => this.listings = listings);
 }
 getListing(id: number) {
  return Promise.resolve(this.listings)
  .then(listings => listings.filter(l => l.id === id)[0]);
 }
 gotoDetail(listing: Listing) {
  this._router.navigate(['ListingDetail', { id: listing.id }]);
 }
}

这可能是什么问题？

Answer 1

您必须将HTTP_PROVIDERS添加到组件providers数组中，如下所示：

providers: [HTTP_PROVIDERS]

或者最好是在这样的引导程序中：

bootstrap(AppComponent, [HTTP_PROVIDERS]);

您错过了constructor中的ListingService http注入：

export class ListingService {
   constructor(private http : Http){}
}

<强>附录

您没有收到任何列表的原因是因为您使用的是Promise而不是Observable：

getListings() ListingService中的

返回此内容：

return this.http.post("bla bla").map(res => res.json).map((res) => {
    return this.listings = res;
});

然后在getListings()中的ListingsComponent订阅

getListings() {
  this.listingService.getListings().subscribe(listings => this.listings = listings);
}

Answer 2

您应该从服务中的请求中返回observable对象：

@Injectable()
export class CompanyService {
  constructor(http:Http/*, routeParams: RouteParams*/) {
    this.http = http;
  }

  getCompanies() {
    return this.http.get('https://angular2.apispark.net/v1/companies/')
            .map(res => res.json());
  }
}

从您的组件订阅一个监听器：

export class CompanyList implements OnInit {
  public companies: Company[];

  constructor(private service: CompanyService) {
    this.service = service;
  }

  ngOnInit() {
    this.service.getCompanies().subscribe(
      data => this.companies = data);
  }
}

希望它可以帮到你，亨利

TypeError：无法读取[null]中未定义的属性'post'

2 个答案: