Description
The FirstItem and LastItem methods always set BoF and EoF correctly but the overhead involved in getting PrevItem and NextItem to do the same may be prohibitive when a filter is in force. By default, i.e. when AggressiveUpdate is false, PrevItem and NextItem only set BoF and EoF when they have tried and failed to move to an earlier (or later) item. Note, therefore, that you can be at the first or last item without BoF/EoF being set correctly. This behavior is similar to that adopted by the BDE.
By setting AggressiveUpdate to true, however, PrevItem and NextItem go to the extra trouble of checking for BoF/EoF. In a large file with a restrictive filter this could prohibitive as it might involve scanning every key.
AggressiveUpdate does not affect the behavior of the other navigation methods since they, by default, do not update the BoF or EoF properties. If you are navigating around a QDB file in this way and you do want BoF/EoF to be maintained (and any attached navigator updated) you can call UpdateNavigator manually.