title: Ask for permission to allow access to Contacts iOS
body: <p>I am importing all the native address book contacts into my app. Currently, the alertview to ask for permission to 'allow access to the Contacts' is done at the launch of the app. </p>
  
  <p>How do I change it so permission is asked elsewhere in the app? At the click of a button, just like Instagram? </p>
  
  <p>See this picture:</p>
  
  <p><img src="https://i.stack.imgur.com/YzHnR.jpg" alt="enter image description here"></p>