title: detecting the change of content of UITextField when the change is not made by the keyboard
body: <p>I have a <code>UIButton</code> and a <code>UITextField</code>,when the button is pressed the textfield's content string will be equal to: <code>This is a test string</code>, how can I detect that this text field has changed its contents in this case?</p>
  
  <p>p.s. <code>UITextField's</code> delegate methods do not work in such case</p>
  
  <p><strong>UPDATE:</strong> I want this behavior to be on iOS 6+ devices.</p>