title: How to check if UITextField's text is valid email?
body: <p>I have a view controller with 3 UITextFields (username, email, and password).</p>
  
  <p>I need a method that checks first, if all fields have text in them, then check if the email's textfield is a valid email, perhaps by checking if it has an <code>@</code> sign in it.  Can anyone help with this?</p>