title: IPostbackEventHandler VS IPostbackDataHandler
body: <p>1)
  User selecting an item in <em>DropDownList</em> is considered to be postback data, and for that reason <em>DropDownList</em> implements <em>IPostbackDataHandler</em>. </p>
  
  <p>a) But why isn’t  user moving ( in <em>Calendar</em> control ) to another month also considered a postback data? Thus, why does <em>Calendar</em> implement <em>IPostbackEventHandler</em> and not <em>IPostbackDataHandler</em>?</p>
  
  <p><br></p>
  
  <p>2)<br>
  a) I assume that controls implementing <em>IPostbackEventHandler</em> instead of <em>IPostbackDataHandler</em> never receive postback data?</p>
  
  <p><br></p>
  
  <p>b) If control implements <em>IPostbackDataHandler</em>, then control’s postback event will be fired each time its data changed, even if that control didn’t caused a postback</p>
  
  <p>But if control implements <em>IPostbackEventHandler</em>, then only time that control’s postback event will be raised is if that control also triggered a postback?</p>