Ionic 2 storage not working on iOS

Ionic 2 storage not working on ios but working on Android. I am using this one import { Storage } from '@ionic/storage'; to store data locally.

I made sample like this

import { Storage } from '@ionic/storage';

export class MyApp {
  constructor(private storage: Storage) { }

  setData() {
    // set a key/value
    storage.set('username', 'johndoe');
  }
  getData() {
    // get a key/value pair
    storage.get('username').then((val) => {
      alert('Your username is', val);
    });
  }
}

It works perfectly on Android. But when I try to build on iOS, it doesn't work. Data is not showing. Some recommendation on how to store persistent data in ionic 2 that works perfectly on android and iOS platforms.