After a research of the current ListView code I suggest a few changes,
that unify the use of an ListView in general.
1) "AllocBy" is a stupid Delphi invention, that better should become
"Capacity". The Capacity property can have a more specific meaning, not
restricted to virtual (OwnerData) listviews, and for compatibility
reasons the AllocBy property can become an alias for Capacity.
2) A "Count" property can be added, that reflects the current number of
listview items. At least in non-virtual mode it should retrieve that
number from the widget, to prevent sychnronization problems. When no
widget exists yet, or the widget doesn't support such a method, the
number of cached listview items can be returned instead (widgetset
specific implementation, as for Capacity).
3) The current cache of *all* (predefined) listview items should be
used/implemented properly. When the widget can be created only after
reading *all* properties, including the predefined items, there exists
no need to duplicate all these items in the widget, i.e. the widget can
run in OwnerData mode internally. Otherwise the item list can be cleared
after the items have been copied into the widget.
3a) In OwnerData mode the ListItems should cache the *actually* required
range of items, visible in the widget. That range should be under
control of the widget or user code, depending on the amount of work and
memory for the creation of the cached items. A default TVirtualListView
class can implement an default cache, eventually with an accordingly
equipped item list class.
4) Many methods can be removed from the current code. In detail the
construction and destruction of the cached items deserves no special
handling, when the ListItems are used as a cache *only*. (see 3).
I'm willing to implement above steps, if there exists any interest.
Since I don't have access to an Mac, can somebody shed some light on the
requirements of that platform, which may conflict with above topics?
Or is the Lazarus team not interested at all, in a *working*
implementation of the listview control? At least I'm missing any
response on my recent patches and messages :-[
DoDi
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