Adding attributes to a control in a datagrid (ASP.NET code)

CODE :

private void dgVanity_ItemCreated(object sender, System.Web.UI.WebControls.DataGridItemEventArgs e)
{
switch(e.Item.ItemType)
{
case (ListItemType.Item) :
TextBox tt = new TextBox();
tt = (((TextBox)(e.Item.FindControl("txtPreferredSpelling"))));
tt.Attributes.Add("onkeyup","validateFloat(this,10,2)");
break;

}

}