On Wed, 19 Feb 2025 01:09:59 GMT, John Hendrikx <[email protected]> wrote:
> I'm going to assume that A and B are aware of each other, and are somehow
> working together, as this scenario makes little sense otherwise. The code
> that is using these two listeners is then likely coming from the same
> implementation (how else would A have a reference to B).
Yes, here is an example:
var property = new SimpleIntegerProperty(0);
ChangeListener<? super Number> listenerB = (obs, ov, nv) -> {
};
ChangeListener<? super Number> listenerA = (obs, ov, nv) -> {
property.set(5);
property.removeListener(listenerB);
};
property.addListener(listenerA);
property.addListener(listenerB);
property.set(1);
> So, given that, if an implementation decides to remove B, no matter when that
> happens exactly (outside a notification call, or within one), would it be
> reasonable to expect a callback still?
Here is how I walked through this in my head:
A gets 0->1; sets 5
A gets 1->5; setting 5 does nothing
B gets 0->5
A removes B (in the 1->5 event)
A removes B (in the 0->1 event)
That is, after A reacts to the new value 5, it's B's turn to react *before*
it's removed. It could be just me though.
> Here is a comparison table:
It looks good, but it doesn't strictly contradict the example. A listener
should stop receiving notifications immediately when it's removed, but here
it's not removed yet and still doesn't receive notifications.
>I feel I also should point out that such dependencies between listeners
>(where listener A removes B, or adds C or whatever) can only happen in code
>that is aware of these other listeners. There is no way to obtain a reference
>to a listener from the system, and so all of these scenario's have perfect
>knowledge of what each listener does and their life cycles. There can be no
>surprises here, listeners can't be added or removed by some other class or
>3rd party dependency without a reference to them.
Yes, this is just another case where I'm not sure we're doing the right thing,
not that I'm sure we're not.
-------------
PR Comment: https://git.openjdk.org/jfx/pull/1081#issuecomment-2667310653
