title: Prevent segue in prepareForSegue method?
body: <p>Is it possible to cancel a segue in the <code>prepareForSegue:</code> method?</p>
  
  <p>I want to perform some check before the segue, and if the condition is not true (in this case, if some <code>UITextField</code> is empty), display an error message instead of performing the segue.</p>