我最近开始玩Angular并试图完成从DB获取一些资源,对它们进行排序和显示它们的简单任务 .
但是组件接收未定义且无法排序 .
我查看了以下主题
angular2 observable, getting undefined in component
angular2 services returns undefined
angular2 observable, getting undefined in component
我在angular.io开始了Google的教程,并根据我的需要扩展/修改了代码
并尝试了以下内容:
服务:
import { Album } from './album';
import { ALBUMS } from './mock-albums';
import { Injectable } from '@angular/core';
import { Headers, Http } from '@angular/http';
import 'rxjs/add/operator/toPromise';
import 'rxjs/add/operator/map';
@Injectable()
export class AlbumService {
private albumURL = '/api/albums';
constructor (private http: Http) { }
getAlbums(): Promise<Album[]> {
return this.http.get(this.albumURL)
.toPromise()
.then(response => {response.json().data as Album[];
console.log(response)})
.catch(this.handleError);
}
还尝试了其他线程建议的getAlbums()体内的以下3个
return this.http.get(this.albumURL)
.map(response => response.json().data as Album[])
.toPromise();
return this.http.get(this.albumURL)
.map(response => {response.json().data as Album[])
return this.http.get(this.albumURL)
.map(response => { return response.json().data as Album[]})
零件:
import { Component, OnInit } from '@angular/core';
import { Album } from './album';
import { AlbumService } from './album.service';
import { Subscription } from 'rxjs/Rx';
@Component({
selector: 'album-dashboard',
templateUrl: 'dashboard.component.html',
styleUrls: [ 'dashboard.component.css' ]
})
export class DashboardComponent implements OnInit {
albums: Album[] = [];
constructor(private albumService: AlbumService) { };
ngOnInit(): void {
this.albumService.getAlbums()
.then(result => this.albums = result.sort((function(a,b){
return (a.artist > b.artist) ? 1 : ((b.artist > a.artist) ? -1 : 0);
})))
}
.... the rest of the class continues
还在组件中尝试了以下内容:
this.albumService.getAlbums()
.subscribe(result => this.albums = result.sort((function(a,b){
return (a.artist > b.artist) ? 1 : ((b.artist > a.artist) ? -1 : 0);
})))
我得到以下错误,并得出结论,由于某种原因,服务在Promise结算之前返回,但我可能是错的
无法读取未定义的属性
需要注意的一点是,上面的服务代码上的console.log(响应)会打印出来自服务器的正确响应 . 因此,数据确实达到了正确的角度服务,但服务和组件之间发生了某些事情
1 回答
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