enable and disable the EDIT button (in action Pane) through SalesTableType class

hi all,
I want to disable the edit button on both SalesTableListPage and SalesTable Form

i have this written code in SalesTableType class and checkUpdate method.

if(salesTable.ConfirmationApprovalStatus == SalesApprovalStatus::Approved )
{
    ok = false;
}

but the problem is that this code is disabling EDIT button only on SalesTableListPage Form not on SalesTable Form.

Please suggest ..
Thanks