title: Allowing single digit in UITextField in iOS
body: <p>I have a <code>Verification ViewController</code>, I get 4 digit verification code by SMS and I need to enter those code to login, I have created the <code>ViewController</code> like this</p>
  
  <p><img src="https://i.stack.imgur.com/oLq5Q.png" alt=""></p>
  
  <p>As you can see four <code>UITextField</code>s, I need to allow only single digit for each <code>UITextField</code>, </p>
  
  <p>What I tried: I was trying to use <code>shouldChangeCharactersInRange:method:</code> , but its not getting called, I don't know what's wrong, I think because <code>UITextField</code>s are in <code>UITableView</code> so it is not working. </p>