Angular 2 : TypeError: Cannot read property 'Symbol(Symbol.iterator)' of undefined

Question

我是 observables 的新手，正在尝试使用 Christoph Burgdorf 的 Observables in Angular2 blog 的基本自动完成变体。 .运行这段代码会产生:

异常:TypeError:无法读取未定义的属性“Symbol(Symbol.iterator)”

在 ingredientservice...rawsearch 中发出 REST get 调用后。警报还会弹出 [object Object] 消息。我已验证端点运行正常。

任何关于如何调试它的建议将不胜感激。

ingredientservice.ts 等待文本字符串的更改、去抖动并执行 REST 调用以从端点获取自动完成匹配项。

import {Injectable} from 'angular2/core';
import {Http} from 'angular2/http';
import {Observable} from 'rxjs/Observable';
import 'rxjs/add/operator/debounceTime';
import 'rxjs/add/operator/distinctUntilChanged';
import 'rxjs/add/operator/switchMap';
import 'rxjs/add/operator/map';

@Injectable()
export class IngredientService {
  endpoint_url: String = "http://localhost:5000/ingredient/";
  results: Observable<Array<string>>;
  constructor(private http: Http) { }

  search(terms: Observable<string>, debounceDuration = 400) {
    return terms.debounceTime(debounceDuration)
      .distinctUntilChanged()
      .switchMap(term => this.rawSearch(term));
  }

  getData: Object[];
  rawSearch(term: string) {
    console.log(term);

    this.http.get(this.endpoint_url + term)
      .subscribe(
      res => {
        this.getData = res.json();
        console.log(this.getData);
        return this.getData;
      },
      error => alert(error));
  }
}

为了完整起见，我包含了组件 ingredientsearch.ts

import {Component} from 'angular2/core';
import {Control} from 'angular2/common';
import {IngredientService} from './ingredientservice';
import {Observable} from 'rxjs/Observable';

@Component({
  selector: 'ingredient-search',
  template: `
    <div>
      <h2>Ingredient Search</h2>
      <input type="text" [ngFormControl]="term"/>
      <ul>
        <li *ngFor="#item of items | async">{{item}}</li>
      </ul>
    </div>
  `,
  providers: [IngredientService]
})

export class IngredientSearch {
  items: Observable<Array<string>>;
  term = new Control();
  constructor(private ingredientService: IngredientService) {
    console.log("About to call service");
    this.items = ingredientService.search(this.term.valueChanges);
  }
}

更新了代码片段并推荐修复。

rawSearch(term: string) {
    this.getData = ([]);
    this.http.get(this.endpoint_url + term)
      .subscribe(
      res => {
        this.getData = res.json();
        console.log(this.getData);
        return this.getData;
      },
      error => {
        alert(error);
      });
    return this.getData;
  }

Answer 1

当 View 绑定(bind)时，项目是未定义的——在服务返回之前。将项目初始化为空数组。或者在模板中使用 Observable 包装器和异步运算符。