open a asp:gridview footer on ext add button click

[landerajshree]

bello,
i have taken ext viewport and border layout.and in center region i have taken a asp:gridview.
but my problem is that i have taken a ext add button for showing a asp:gridview footer..but its nt working

here is my codebehind addbtn code

protected void btnadd_Click(object sender, DirectEventArgs e)
{
Gridview1.FooterRow.Visible = true;


}

please tell me how to do that.......

regards,
Rajshree.