I have an iframe that shows a graph, controlled by a form. I already included in the script to show a loading gif when the iframe is loading. However this gif only appears when the iframe is loaded for the first time. However, when I make changes in the form to display the data I want to see, the iframe reloads to show a new graph, but the 'loading' gif does not reappear. How can I fix this? this is the code I already have for the loading gif:

<form id="form1" runat="server">
    <div id="divLoading">
    <img src="images/loading.gif" alt="" />
    <div id="divFrameHolder" style="display:none"> 
<iframe src="grafiek.php" width="800" height="400" name="grafiek" onload="hideLoading()" frameborder="0" marginwidth="0" marginheight="0" scrolling="no" align="middle" allowtransparency="true"></iframe>