The dive list is fed data by means of a sorted "DiveTripModel".
There are two modes: list and tree. This was implemented rather
elegantly with a general "TreeModel", which can represent trees
of arbitrary depths.
Nevertheless, we have at most two levels and on the second level
only dives can reside. Implementing proper model-semantics
(insert, delete, move) will be quite a challenge and implementing
it under the umbrella of a very general model will not make it
easier.
Therefore, for now, hardcode the model:
At the top-level there are items which may either be a trip
(can contain multiple dives) or a dive (contains exactly one dive).
Thus, we can completely de-virutalize the DiveItem and TripItem
classes, which are now trivial wrappers around dive * and dive_trip *.
Signed-off-by: Berthold Stoeger <bstoeger@mail.tuwien.ac.at>
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