Angular 2.安排一项服务

我有一个ionic 2项目，客户通过定制提供商调用的服务检查剩余的单元。此时，客户可以输入参考号，供应商将一如既往地返回设备，一切正常。我想要的是在后台定期呼叫此服务，比如说每30分钟检查一次，以便当单位低于某个值时，我可以通知客户

GetUnitsProvider:

    import { Injectable } from '@angular/core';
    import { Http } from '@angular/http';
    import 'rxjs/add/operator/map';
    import { Observable } from 'rxjs/Rx';
    import { Meter } from '../models/meters';

    @Injectable()
    export class GetUnitsProvider {
      constructor(public http: Http) {} 
        // get the customer units
        loadUnitsBalance(id:number): Observable<Meter[]> {
        return this.http.get(`http://example.com/balance.pl?referencenumber=${id}&api=json`)
          .map(res => <Meter[]>res.json());
        }
    }

为您服务：

constructor(public http: Http) {
  Observable.interval(30 * 60 * 1000)
            .switchMap(this.http.get(`...`))
            .map(res => res.json())
            .subscribe(res => this.check(res))
}

private check(res: <Meter[]>) {
  // check whether to notify the user
}

constructor(public http: Http) {
  Observable.interval(30 * 60 * 1000)
            .switchMap(this.http.get(`...`))
            .map(res => res.json())
            .subscribe(res => this.check(res))
}

private check(res: <Meter[]>) {
  // check whether to notify the user
}

providers: [
    {
        provide: APP_INITIALIZER,
        use: GetUnitsProvider,
        deps: [Http],
        multi: true
    }
],