Back in 2010, in the thread about observer support in fcl, i asked if the
actions would be customizable so i could, e.g., notify/observe if a child was
added or removed in a tree structure. The answer was yes.
Looking at the recent added support, it limit the actions (called operations)
to 5 types
TFPObservedOperation = (ooChanged,ooFree,ooAddItem,ooDeleteItem,ooCustom);
I ask to change to a mechanism that could allow customizable operations (more
than one)
I'm asking that because i have implemented a similar mechanism that support
operations like Load, ChildAdd, ChildDelete, ChildChange. I believe that more
developers are in the same situation,i.e., using observer pattern to an action
not handled by those 5 types. It would be helpful to use the native
implementation otherwise i will have to keep(re-implement) the observer support
over TPersistent.
BTW:
The names of the TFPObservedOperation are not consistent:
ooChanged is in preterit while others not
ooChanged does not has Item suffix
it should be
ooChange,ooAdd,ooDelete
or
ooChanged,ooAdded,ooDeleted
or
ooChangeItem,ooAddItem,ooDeleteItem
or
ooChangedItem,ooAddedItem,ooDeletedItem
The changes: http://svn.freepascal.org/cgi-bin/viewvc.cgi?view=rev&revision=22257
See the cited email:
Michael Van Canneyt escreveu:
On Thu, 20 May 2010, Florian Klaempfl wrote:
I've no opinion if it's usefull to add or not, I use TPersistent+ too
little but my concern is: if I create an observer for an instance, I'd
expect to get notified about every change to the instance. But I cannot
see how this will be achieved, no existing class is prepared for this?
Not every change. What you get notified about is defined by the class
that uses the observable interface. TStrings will notify you of
additions/removals, and TList/TObjectList as well.
It will send some kind of info (like index or address of the object) to
know what and where the item was added or removed?
Yes.
Can the same Obsever observe (:-D) more than of one type of object? e.g.
i want to observe a object list for adding or removals, but also want to
know if one of the child objects changed.
Yes. You can observe any object that will implement the IFPObservable
interface.
Michael.
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