title: AutoCompleteTextView allow only suggested options
body: <p>I have a <code>DialogFragment</code> that contains <code>AutoCompleteTextView</code>, and <code>Cancel</code> and <code>OK</code> buttons.</p>
  
  <p>The <code>AutoCompleteTextView</code> is giving suggestions of usernames that I'm getting from server.</p>
  
  <p>What I want to do is to restrict the user to be able to enter only existing usernames.</p>
  
  <p>I know I can do check if that username exists when the user clicks <code>OK</code>, but is there some other way, let's say not allow the user to enter character if there doesn't exist such username. I don't know how to do this because on each entered character I'm getting only up to 5 suggestions. The server is implemented that way.</p>
  
  <p>Any suggestions are welcomed.
  Thank you</p>