title: How to fire the `valueChanges` programmatically?
body: <p>On one of my pages I use a <code>FormBuilder</code> to fill a form at initialization. Every input gets a class whenever the input is <strong>not</strong> empty. This is done by adding a <code>ngClass</code> to every input, and subscribing on the <code>FormGroup</code>'s <code>valueChanges</code>.</p>
  
  <p>My problem occurs whenever the form is filled programmatically. Whenever a user changes any value on the form, <code>valueChanges</code> gets called, however, this is not the case when using a <code>FormBuilder</code>.</p>
  
  <p>My question is: How to get the <code>valueChanges</code> event to be fired whenever the <code>FormBuilder</code> is finished.</p>
  
  <p>I have tried using <code>this.FormGroup.updateValueAndValidity()</code>, but this did not result in anything.</p>