title: NativeScript: Disable all controls while ActivityIndicator is shown
body: <p>Lets say there is a login page with username\password TextFields and login Button. When the button is pressed a request is set to a server and ActivityIndicator is shown.
  Currently I put StackLayout on top of all other controls not to give the user a possibility to click on them while processing the request. But in some cases TextField stays focused and the user can type there.</p>
  
  <p>I'm already using a component to wrap all TextFields to show validation errors:</p>
  
  <pre><code>@Component({
    selector: "field",
    template: "&lt;grid-layout&gt;&lt;ng-content&gt;&lt;/ng-content&gt;...&lt;/grid-layout&gt;"
  })
  export class FieldComponent {
    @ContentChild(NgModel) private input: NgModel;
    ...
  }
  </code></pre>
  
  <p>My question is can I set isEnabled property to false on TextField inside <code>ng-content</code> from <code>FieldComponent</code> having <code>NgModel</code> or in some another way?
  If it is impossible what is the best practices in this case to disable inputs when an app is busy? </p>