[fpc-devel] Tests of observer feature [was: Considerations about observer]

[michael.vancanneyt at wisa.be]

On Thu, 29 Nov 2012, Graeme Geldenhuys wrote:

> Hi Luiz,
>
> First off, thanks for take the trouble it creating test projects.
>
>
> On 2012-11-29 02:59, luiz americo pereira camara wrote:
>>
>> Test1
>> As is today, if you have a reference to a IFPObserver is not possible
>> to use it to attach to, e.g., child objects. This occurs because AFAIK
>> you can't get a TObject from a interface reference.
>
>
> OK, there are quite a few things I consider wrong with your Test1
> application.
>
> 1) Nothing stops Michael from extending the IPFObserver interface to
>    include a GetObject function that returns a TObject reference of
>    the observer.
>    I have seen many such cases in the wild. Not sure if I agree
>    with it, but that is another story.
>
> 2) What exactly are you observing in Test1? What are you trying to
>    accomplish?
>    TMyParentView is a TObject. Adding children to the Children property
>    doesn't notify the observer about anything.
>    ... now if the Observer property is holding reference to something
>    that should observer each of the Children, well, then that is very
>    easy to accomplish too. Simply changes the Observer property to
>    a TObject instance.
>
> 3) Something Michael should fix. TFPObjectList doesn't support
>    IPFObserver. TObjectList does though. I guess many of the list
>    classes in the Contnrs unit should be double checked.

No. This is left out on purpose.

If you want observer support, you need TObjectList and TList.

The primary reason of existence for TFPList and TFPObjectList is speed and
minimal overhead. TList and it's observer/notification capabilities introduce 
a serious speed penalty.

For instance when doing a Clear, all items are removed one by one as opposed 
to just de-allocating the array used to hold them.

Michael.