Angular2:TypeError:无法读取未定义的属性“Symbol(Symbol.iterator)" [英] Angular2: TypeError: Cannot read property 'Symbol(Symbol.iterator)' of undefined

问题描述

我是 observables 的新手，正在试验 Christoph Burgdorf 的 Angular2 博客中的观察值.运行此代码会产生:

例外:类型错误:无法读取未定义的属性 'Symbol(Symbol.iterator)'

在成分服务中发出 REST get 调用后...rawsearch.警报还会弹出 [object Object] 消息.我已验证端点运行良好.

关于如何调试的任何建议将不胜感激.

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.

import {Injectable} from 'angular2/core';从'angular2/http'导入{Http}；从 'rxjs/Observable' 导入 {Observable}；导入 'rxjs/add/operator/debounceTime';导入 'rxjs/add/operator/distinctUntilChanged';导入 'rxjs/add/operator/switchMap';导入 'rxjs/add/operator/map';@Injectable()导出类 IngredientService {endpoint_url: String = "http://localhost:5000/ingredient/";结果:Observable>；构造函数(私有http:Http){}搜索(条款:可观察的<字符串>，去抖动持续时间= 400){返回terms.debounceTime(debounceDuration).distinctUntilChanged().switchMap(term => this.rawSearch(term));}获取数据:对象[]；原始搜索(术语:字符串){控制台日志(术语)；this.http.get(this.endpoint_url + term).订阅(资源=>{this.getData = res.json();console.log(this.getData);返回 this.getData;},错误 =>警报(错误))；}}

为了完整起见，我包含了 ingredientsearch.ts

组件

import {Component} from 'angular2/core';从'angular2/common'导入{Control}；从'./ingredientservice'导入{IngredientService}；从 'rxjs/Observable' 导入 {Observable}；@成分({选择器:'成分搜索'，模板:`<div><h2>成分搜索</h2><input type="text" [ngFormControl]="term"/><ul><li *ngFor="#item of items | async">{{item}}</li>

`，提供者:[成分服务]})导出类 IngredientSearch {项目:可观察的<数组<字符串>>；term = new Control();构造函数(私有成分服务:成分服务){console.log("即将调用服务");this.items =成分服务.search(this.term.valueChanges);}}

使用推荐的修复更新了代码片段.

rawSearch(term: string) {this.getData = ([]);this.http.get(this.endpoint_url + term).订阅(资源=>{this.getData = res.json();console.log(this.getData);返回 this.getData;},错误 =>{警报(错误)；});返回 this.getData;}

解决方案

在绑定视图时 - 在服务返回之前未定义项.将 items 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.

I'm new to observables and experimenting with an basic autocomplete variation of Christoph Burgdorf's Observables in Angular2 blog. Running this code produces:

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

after issuing the REST get call in ingredientservice...rawsearch. The alert also pops with an [object Object] message. I've verified the endpoint is running fine.

Any recommendations on how to debug this would be greatly appreciated.

ingredientservice.ts waits for a change on a text string, debounces it and performs a REST call to get autocomplete matches from an endpoint.

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));
  }
}

for completeness I have included the component 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);
  }
}

Updated code snippet with recommended fix.

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;
  }

解决方案

Items is undefined when the view is bound - before the service returns. Initialize items to an empty array. Or use an Observable wrapper and the async operator in your template.

这篇关于Angular2:TypeError:无法读取未定义的属性“Symbol(Symbol.iterator)"的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！