title: how to use event onChange in ionic2
body: <p>Basically I am trying to make a registration form in which I have some drop down lists. And I want to apply "(change)" event on it which will trigger a function whenever value will be changed or we can say value be selected from that drop down list and based on that I will be assigning next fields dynamically but this event is not working on drop-down while its working fine with text fields.
  Can someone help me out with this?</p>
  
  <p>Sample code:</p>
  
  <p>home.html --></p>
  
  <pre><code>&lt;ion-header&gt;
    &lt;ion-navbar&gt;
      &lt;ion-title&gt;Home&lt;/ion-title&gt;
    &lt;/ion-navbar&gt;
  &lt;/ion-header&gt;
  &lt;ion-content padding&gt;
  
  &lt;form [formGroup]="myForm"&gt;   
      &lt;ion-item&gt;
          &lt;ion-label&gt;Dropdown1 :&lt;/ion-label&gt;
          &lt;ion-select formControlName="dd" (ionChange)='f()'  #dd&gt;
           &lt;ion-option value='1'&gt;A&lt;/ion-option&gt;
              &lt;ion-option value='2'&gt;B&lt;/ion-option&gt;
              &lt;ion-option value='3'&gt;C&lt;/ion-option&gt;
              &lt;ion-option value='4'&gt;D&lt;/ion-option&gt;
          &lt;/ion-select&gt;
      &lt;/ion-item&gt;
  
       &lt;ion-item&gt;
      &lt;ion-label&gt;Dropdown2 :&lt;/ion-label&gt;
      &lt;ion-select&gt;
       &lt;ion-option value='1'&gt;E&lt;/ion-option&gt;
          &lt;ion-option value='2'&gt;F&lt;/ion-option&gt;
          &lt;ion-option value='3'&gt;G&lt;/ion-option&gt;
          &lt;ion-option value='4'&gt;H&lt;/ion-option&gt;
      &lt;/ion-select&gt;
  &lt;/ion-item&gt;
  
  &lt;/form&gt; 
  &lt;/ion-content&gt;
  </code></pre>
  
  <p>home.ts --></p>
  
  <pre><code>import { Component } from '@angular/core';
  
  import { NavController } from 'ionic-angular';
  
  @Component({
    selector: 'page-home',
    templateUrl: 'home.html'
  })
  export class HomePage {
  
    constructor(public navCtrl: NavController) {
  
    }
  
    function f(){
    alert('Value Changed!');
    alert(this.myForm.dd);
  
    }
  
  }
  </code></pre>