title: Determining which control caused PostBack
body: <p>I have this aspx:</p>
  
  <pre><code>&lt;asp:ImageButton ID="check" runat="server" ImageUrl="../img/process.png"  OnClick="check_Click" CausesValidation="false" UseSubmitBehavior="false"/&gt;
  </code></pre>
  
  <p>now in <code>Page_Load</code> I want to determine that is <code>PostBack</code> caused by <code>check</code> or no so I followed <a href="https://stackoverflow.com/questions/7269271/which-control-caused-the-postback">this</a> question's method with this code:</p>
  
  <pre><code>if(FindControl(Page.Request.Params.Get("__EVENTTARGET"))!=check)//if not caused by "check"
      //do something
  </code></pre>
  
  <p>but <code>Page.Request.Params.Get("__EVENTTARGET")</code> is empty .(I'm using my <code>ImageButton</code> in <code>UpdatePanel</code>)</p>
  
  <p>How can I reach to my goal?</p>