以角度每 x 秒发出一次 http 请求

I'm trying to refresh an http call every x seconds in angular2.

  ionViewDidLoad() {

    let loader = this.LoadingController.create({
      'content':'Please Wait'
    });
    loader.present().then(()=>{
      this.http.request('http://mywebserver.com/apps/random.php').map(res=> res.json()).subscribe(data=>{
        console.log(JSON.stringify(data));
        loader.dismiss();
        this.fact = data;
      },err=>{
        loader.dismiss();
        let alert = this.alertCtrl.create({
          title: 'Error!',
          subTitle: 'Please check your Internet Connectivity',
          buttons: ['OK']
        });
      alert.present();
    })
    })

  }

我在页面新加载时获取数据.但现在我的问题是刷新 http 调用以每 x 秒获取新数据

import {Observable} from 'rxjs/Rx';
...
constructor(...) {
  Observable.interval(30000).subscribe(x => { // will execute every 30 seconds
    this.ionViewDidLoad();
  });
}

Observable.interval(3000)
          .timeInterval()
          .flatMap(() => this.http.request('http://mywebserver.com/apps/random.php')
          .map(res=> res.json())
          .subscribe(data=>{
              console.log(JSON.stringify(data));
              loader.dismiss();
              this.fact = data;
            });