>How to prevent entering new values ?
>Which is the best way to mark list box read only from VFP code ?

If my combo is read-only, then I don't want the user to be able to show the list of values, either. Therefore, something like this in the ReadOnly_ASSIGN method works for me:

LPARAMETERS lReadOnly

THIS.Enabled = !lReadOnly
IF lReadOnly
   THIS.DisabledForeColor = THIS.ForeColor
ELSE
   THIS.ResetToDefault("DisabledForeColor")
ENDIF

THIS.ReadOnly = m.lReadOnly