Pull to refresh not working in my App

Ionic Framework ionic-v3
1

Pull to refresher not working anyone can help me

TS

  ionViewDidEnter() {

		this.http.get( this.url )
	    .map(res => res.json())
	    .subscribe(data => {
	      // we've got back the raw data, now generate the core schedule data
	      // and save the data for later reference
	      this.items = data;
	    });
	}
	
	doRefresh(refresher){
    this.http.get(this.url) . subscribe ((data) => {
      this.items = data;
 
      if(refresher != 0)
         refresher.complete();
    }); 
};

HTML

<ion-content>
<ion-refresher (ionRefresh)="doRefresh($event);">
    <ion-refresher-content 
      pullingText="Pull to refresh"
      pullingIcon="arrow-dropdown"
      refreshingSpinner="circles"
      refreshingText="..fetching">
    </ion-refresher-content>
 </ion-refresher>
</ion-content>