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如下所示：
import {Component,OnInit} from 'angular2/core';
import {HTTP_PROVIDERS,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 }]);
}
}
这有什么问题？
您必须将HTTP_PROVIDERS添加到组件提供程序数组,如下所示：
原文链接：https://www.f2er.com/angularjs/142404.htmlproviders: [HTTP_PROVIDERS]
或者最好是在这样的引导程序中：
bootstrap(AppComponent,[HTTP_PROVIDERS]);
而且你在ListingService中缺少构造函数http注入：
export class ListingService {
constructor(private http : Http){}
}
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：
在ListingService中的getListings()中返回：
return this.http.post("bla bla").map(res => res.json).map((res) => {
return this.listings = res;
});
然后在ListingsComponent的getListings()中订阅这个：
getListings() {
this.listingService.getListings().subscribe(listings => this.listings = listings);
}
