title: Activity Indicator is not visible on xaml page in xamarin.forms?
body: <p>I have an activity indicator on xaml page. Initially its IsVisible property is false. I have a button on page. When user click on button it calls a web service to get data. I change the value of IsVisible property to true before calling the service so that activity indicator starts to display on page and after successful calling of service I change its value to again false so that it doesn't show any more on page. </p>
  
  <p>But it is not working. I know the actual problem. When we call the web service the UI thread gets block and it doesn't show the activity indicator. 
  How I can enable the UI thread when web service gets called so that activity indicator can show on page until we get the data?</p>