Question

我尝试访问管道中的缓存数据，但总是收到以下错误：

Cannot read property 'subscribe' of undefined

服务：

import { Injectable } from '@angular/core';
import {Observable} from 'rxjs/Rx';
import 'rxjs/observable/of';
import 'rxjs/add/operator/map';

@Injectable()
export class FormDataService {

  private apiUrl = "http://localhost";
  private data:any;
  private observable: Observable<any>;

  constructor(
    private _http: Http
  ){}

  getCountries() {
    if(this.data) {
      console.log("data available");
      return Observable.of(this.data);
    } else if(this.observable) {
      console.log("request pending")
      return this.observable;
    } else {
      console.log("request data");
      this.observable = this._http.get(this.apiUrl + "/country")
        .map(res => {
          console.log("data received");
          this.observable = null;
          this.data = res.json();
        });
    }
  }

管道：

export class ResolvePipe implements PipeTransform {

  constructor(
    public _formDataService: FormDataService
  ) {}

  transform(value: number, args: any[]): any {
    return this._formDataService.getCountries().subscribe(
      data => {
        console.log(data);
        return data;
      }
    )
  }
}

我有另一个问题：

api返回一个对象数组

[{id:1,label:"USA",id:2, label:"DE", ...}]

管道应该用标签替换id（值）...你会在哪里这样做？在服务或管道？

编辑：

formdata.service.ts:27 request data
formdata.service.ts:30 data received
formdata.service.ts:27 request data
formdata.service.ts:24 request pending (822 times)
formdata.service.ts:30 data received

Answer 1

缺少回复

  getCountries() {
    if(this.data) {
      console.log("data available");
      return Observable.of(this.data);
    } else if(this.observable) {
      console.log("request pending")
      return this.observable;
    } else {
      console.log("request data");
      this.observable = this._http.get(this.apiUrl + "/country")
        .map(res => {
          console.log("data received");
          this.observable = null;
          this.data = res.json();
        });
      return this.observable; // <<<<
    }
  }

否则将返回null，null不提供subscribe方法。

无法订阅缓存服务

1 个答案: