title: Check if a ComboBox value is selected
body: <p>I'm writing a form which includes some buttons and a combo box.
  The "Ok" button is disabled by default, and I wish to enable it only after an actual value (not the combo box's name) is selected.</p>
  
  <p>I know how to access the selected value, and how to check if a value has been selected - but these two can be done only after the form is close (using the"x" or using the "ok" button - which is disabled).</p>
  
  <p>Any ideas?</p>
  
  <p>Thanks.</p>