title: Showing an error message on form submit in angular2?
body: <p>I have implemented model driven form in <a href="http://plnkr.co/edit/HzZsf1DEbRTcwSyzyStu?p=preview" rel="noreferrer">this demo</a>. If the user doesn't enter anything and submits the form I am showing an error message using this logic</p>
  
  <pre><code>&lt;div *ngIf="(!myForm.find('sku').valid &amp;&amp; submitted)"&gt;**sku is required&lt;/div&gt;
  </code></pre>
  
  <p>I am passing a boolean variable 'submitted' to check whether a control is valid or not when submitted. Is there any way to check the state of the control without passing a variable manually? Angular2 forms gives us 6 classes like <code>ng-touched</code>, <code>ng-untouched</code>, <code>ng-valid</code>, <code>ng-invalid</code>, <code>ng-pristine</code>, and <code>ng-dirty</code>. I want to show the error message using only these classes.</p>