离子存储以 Aync 方式获取值

Question

>我正在尝试在离子存储中存储 2 个值，但该值以异步方式重新生成，并且在值被重新引用之前正在发生请求

这里身份验证，url在离子存储中

import { Injectable } from '@angular/core';
import { Http, Response } from '@angular/http';
import 'rxjs/add/operator/map';
import {Headers} from '@angular/http';
import { Storage } from '@ionic/storage';
/*
  Generated class for the SeasonService provider.
  See https://angular.io/docs/ts/latest/guide/dependency-injection.html
  for more info on providers and Angular 2 DI.
*/
@Injectable()
export class SeasonService {
Auth;
url;
  constructor(public http: Http, public storage: Storage) {
    console.log('Inside SeasonService constructor');
    this.storage.get('Auth').then((Auth) => {
      console.log('Retrived Auth is', Auth);
      this.Auth = Auth;
    } );
    this.storage.get('url').then((url) => {
      console.log('Retrived url is', url);
      this.url = url;
    } );
   }
  public getSeasonList() {
          console.log('Season Auth is', this.Auth);
          console.log('Season url is', this.url);
        const headers: Headers = new Headers();
        headers.append('Authorization', 'Basic ' + this.Auth);
        headers.append('Content-Type', 'application/json');
        return (this.http.get('http://' + this.url +'/Windchill/servlet/rest/rfa/instances?module=SEASON',
        {headers: headers}).
        map((response: Response) =>  response.json()));
      }
}

输出是这样的

Here
auth-service.ts:49 Headers {_headers: Map(2), _normalizedNames: Map(2)}
auth-service.ts:77 There
season-service.ts:19 Inside SeasonService constructor
season-service.ts:34 Season Auth is undefined
season-service.ts:35 Season url is undefined
season-service.ts:22 Retrived Auth is d2NhZG1pbjp3Y2FkbWlu
season-service.ts:27 Retrived url is 192.168.146.52
auth-service.ts:79 Your CSRF is laxYnd5XE6d/r+W655087+8dY5Irxc7do94fxLgvY5ImgNeIwsgI1bYaQdAzxZDM5sMZsqgbXppFntGDoJhrq+puJJROnN+N1MEcy7d4Js8ozs7Oxpwfpe0zRvcIktg=
auth-service.ts:82 Your Auth is d2NhZG1pbjp3Y2FkbWlu
auth-service.ts:85 Your url is 192.168.146.52

Answer 1

在提出请求之前，您必须等待两个承诺得到解决。首先将存储代码移动到某种init方法。

public init(){
let promiseList: Promise<any>[] = [];
promiseList.push(
 this.storage.get('Auth').then((Auth) => {
      console.log('Retrived Auth is', Auth);
      this.Auth = Auth;
    } ));
promiseList.push(
    this.storage.get('url').then((url) => {
      console.log('Retrived url is', url);
      this.url = url;
    } ));
return Promise.all(promiseList);
}

现在在getSesonList之前调用init方法，如下所示：

this.sessionService.init().then((values)=>{
this.sessionService.getSeasonList();
});

这将确保在解析两个存储承诺后调用 getSeasonList 方法。

显然，您应该放置一些错误处理代码，但它取决于您。