使用Observable的Angular2 HTTP订阅显示未定义的数据

Question

我不知道自己在做错什么，但是以某种方式我无法读取数据，尽管当我放入控制台时，数据是作为响应来自服务器的，甚至数据也已显示在服务extractData方法中，但是在订阅函数内部的组件中，它给了我未定义的信息。 帮帮我，我做错了，我假设这是异步的问题，但是，我不知道该如何纠正。 任何帮助将是可观的。 提前感谢

Component.ts

import { Component, Input, OnInit } from '@angular/core';
import {AdminService} from './admin.service';
import {logistics} from '../shared/model/logistics';
import 'rxjs/add/operator/map';
import 'rxjs/add/operator/catch';
import 'rxjs/add/operator/debounceTime';
import 'rxjs/add/operator/distinctUntilChanged';
import 'rxjs/add/operator/switchMap';
import 'rxjs/add/operator/toPromise';
import { Observable }     from 'rxjs/Observable';
import {Response } from '@angular/http';
@Component({
    moduleId:module.id,
    selector: 'admin',
    templateUrl: 'admin.component.html',
    styleUrls:['admin.component.css'],
    providers:[AdminService]
})

export class AdminComponent implements OnInit{
   @Input() public allocatedAssetsList: logistics[];


    mode = 'Observable';
    public errorMsg = '';
    constructor(private adminService: AdminService) {

    }

    ngOnInit(){
        this.listByEmpId("123");

    }

    listByEmpId(empId:string){

        this.adminService.getAllocatedAssets(empId).subscribe(
        res => this.allocatedAssetsList = res,
        error =>  this.errorMessage = <any>error);
    }
}

服务

import { Injectable }     from '@angular/core';
import { Http, Response } from '@angular/http';
import { Hero }           from './hero';
import { Observable }     from 'rxjs/Observable';
import { Headers, RequestOptions } from '@angular/http';
import {logistics} from '../shared/model/logistics';
import 'rxjs/add/operator/map';
import 'rxjs/add/operator/catch';
import 'rxjs/add/operator/debounceTime';
import 'rxjs/add/operator/distinctUntilChanged';
import 'rxjs/add/operator/switchMap';
import 'rxjs/add/operator/toPromise';


@Injectable()
export class AdminService {
    constructor (private http: Http) {}
    private listAssetsURL = '/api/logistics/list/';  // URL to web API

    private extractData(res: Response) {
        let body = res.json();
        return body || { };
    }

    private handleError (error: any) {
        // In a real world app, we might use a remote logging infrastructure
        // We'd also dig deeper into the error to get a better message
        let errMsg = (error.message) ? error.message :
            error.status ? `${error.status} - ${error.statusText}` : 'Server error';
        console.error(errMsg); // log to console instead
        return Observable.throw(errMsg);
    }

    getAllocatedAssets (empId: string): Observable<logistics[]> {

        this.listAssetsURL+= empId;
        //let body = JSON.stringify({ empId });
        let headers = new Headers({ 'Content-Type': 'application/json' });
        let options = new RequestOptions({ headers: headers });

        return this.http.get(this.listAssetsURL)
            .map(this.extractData)
            .catch(this.handleError);
    }
}

Answer 1

listByEmpId(empId:string){

    this.adminService.getAllocatedAssets(empId).subscribe(
    res => {
      this.allocatedAssetsList = res;
      console.log(this.allocatedAssetsList);
    },
    error =>  this.errorMessage = <any>error);
}

Answer 2

这可能是因为您试图在实际从服务返回数据之前访问您的locatedAssetsLists。

如果要在模板中访问它，则可以使用简单的ngIf来确保仅在数据可用后才尝试显示它。

如果不是这样，我们需要有关您的问题的更多信息以提供帮助。