怎么触发gridview 的SelectedIndexChanged事件?

<asp:GridView onclick="javascript:SelectedIndexChanged()" ID="GridView1" runat="server">
        </asp:GridView>

<script type="text/javascript">
function SelectedIndexChanged()
{
     event.cancelBubble=true;
     var the_obj = event.srcElement;

if(the_obj.tagName.toLowerCase() != "table" && the_obj.tagName.toLowerCase() != "tbody" && the_obj.tagName.toLowerCase() != "tr")
     {
         cur_row = the_obj.parentElement.rowIndex;
if(cur_row!=0)
{
     __doPostBack("GridView1",cur_row);
}
      }
}
</script>