get postback value from iframe

Hi all, I have a page with iframe. The idea is to change some data on my page without postback by using iframe postback with width=0px After the btnParent was clicked I needed to send data to the iframe. I click iframe button with javascript. Then parent control txtParent2 have to get data from iframe. It almost worked but txtParent2 .Text is empty. What's wrong? *********************** My test Parent Page: ************************ <%@ Page Language="C#" %> <!DOCTYPE html> <script runat="server"> </script> <html xmlns="http://www.w3.org/1999/xhtml"> <head runat="server">     <title>ParentPage</title>  <script type="text/javascript">      function clickIframeButton() {          hiddenFrame.do ...