OnRowEditing event. Add this code to call javascript function from back code(Code behind)
Page.ClientScript.RegisterStartupScript(this.GetType(),"CallMyFunction","HideTextBox()",true);
Now on your .aspx page, write below code block
<script type="text/javascript">
function HideTextBox(){
$('#<%= IDSrch.ClientID %>').hide();
}
</script>
Make sure you put javascript code on .aspx page(not in any .js file). hope this will solve your problem.