<html><head><meta http-equiv="content-type" content="text/html; charset=utf-8"></head><body style="overflow-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;"><div><br></div><div><div><blockquote type="cite"><div>On Jan 13, 2026, at 9:35 AM, Andy Goryachev <andy.goryachev@oracle.com> wrote:</div><div><div><div dir="ltr" style="font-family: "Iosevka Fixed SS16", Arial, Helvetica, sans-serif; font-size: 12pt;"><br></div>
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I do want to ask Martin one thing though: what do you mean by "The only obvious gap in the public API is that there’s no way for a handler or filter to communicate with the dispatcher that invoked it." Can you give an example?</div></div></div></blockquote><div><br></div><div>This PR is the example. The Control class could implement primary and default handlers itself using existing mechanisms like rolling its own dispatchers. The only part it can’t do is have a primary handler communicate to the dispatcher that the default handlers should be skipped. There’s no existing mechanism for that; the only communication in that direction is the `consumed` bit. This PR had to add a global bit to all Events just for that.</div><div><br></div><div>Again, that global bit might be the best solution. It’s based on an existing web event standard and is easy to define and to ignore if it’s not appropriate for a given source. Engineering a more general solution might be a waste of time.</div></div><div><br><blockquote type="cite"><div><div><div dir="ltr" style="font-family: "Iosevka Fixed SS16", Arial, Helvetica, sans-serif; font-size: 12pt;">
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Thanks!</div>
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-andy</div>
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<b>From: </b>openjfx-dev <openjfx-dev-retn@openjdk.org> on behalf of Martin Fox <martinfox656@gmail.com><br>
<b>Date: </b>Tuesday, January 13, 2026 at 09:00<br>
<b>To: </b>John Hendrikx <john.hendrikx@gmail.com><br>
<b>Cc: </b>OpenJFX <openjfx-dev@openjdk.org><br>
<b>Subject: </b>Re: [External] : Re: Default event handlers<br>
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<div class="ms-outlook-mobile-reference-message skipProofing">I didn’t intend to re-open all of these debates. I just wanted to point out that JavaFX in general uses dispatchers to process events so there’s no existing concept of default handlers outside of
Control. If Control had implemented InputMap using a dispatcher we probably wouldn’t be having this conversation.</div>
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<div class="ms-outlook-mobile-reference-message skipProofing">I still believe this is a local problem for Control and it can craft its own solution. It doesn’t even have to involve handlers; look at how Scene and Menu handle accelerators. Whatever Control wants
to do almost all of the tools are there. The only obvious gap in the public API is that there’s no way for a handler or filter to communicate with the dispatcher that invoked it. Rather than add a specialized bit like this PR does I thought it might be worth
considering a more generalized solution (I can think of a few) but I’m actually fine with preventDefault() since it’s based on an existing standard.</div>
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<div class="ms-outlook-mobile-reference-message skipProofing">Martin</div>
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<div class="ms-outlook-mobile-reference-message skipProofing">On Jan 13, 2026, at 4:52 AM, John Hendrikx <john.hendrikx@gmail.com> wrote:</div>
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<div class="moz-cite-prefix">On 13/01/2026 00:43, Andy Goryachev wrote:</div>
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The reason I mentioned #2 is that it is somewhat relevant to the discussion, as in "why do we need to write custom dispatchers at all?" There should be only two methods, in my opinion, one that dispatches an event that bubbles up (with filters and handlers),
and one that sends an event to a single target Node and nothing else. <rant>Somehow, Swing got the Events right - it manages to dispatch one (1) event in total, and the dispatching stops once the event is consumed. The FX decided it needed to reinvent the
wheel and leave multiple booby traps in the process.</rant></div>
</blockquote><p class="ms-outlook-mobile-reference-message skipProofing">Although I agree that how FX solved events is sub-optimal, there is a real need here to communicate to the EventHandler on which object it resides. EventHandler instances are expensive when you need
to attach one to every Cell in a TableView, and so to re-use a single instance, you need to know which Cell the event applies to. The source field (which is supposed to be constant) has been abused for this, making events non-constant requiring cloning before
they can be dispatched to their final target. This cloning then caused the "isConsumed" problem. Perhaps we should just make the source field mutable as well, so the cloning isn't needed.</p><p class="ms-outlook-mobile-reference-message skipProofing">The solution to this problem at the time should not have been to modify events, but to have made event handlers be BiConsumers, with the Event **and** Node being passed to the callback (and a "convenience"
method that delegates to the BiConsumer variant that accepts only Consumer<Event> -- we may be able to still do this...)</p>
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This isn't exactly rocket science, we should be able to figure something out. Maybe there is another option that will satisfy everyone?</div>
</blockquote><p class="ms-outlook-mobile-reference-message skipProofing">I think the issue isn't so much in event dispatching, but in the Skin/Behavior system itself. Skin/Behaviors in FX is like giving root access to every user on your system. Sure it is convenient that
everyone can do whatever they want, and as long as everyone behaves, everything works great. However one malicious user can interfere with others or leave behind hooks that later come to bite you.</p><p class="ms-outlook-mobile-reference-message skipProofing">Controls are HOSTS for Skins and Behaviors. Skins and Behaviors are clients. They should be restricted to a very specific subset of functionality that benefits the host and is predictable for the
host:</p><p class="ms-outlook-mobile-reference-message skipProofing">- Skins get ownership of the children list of the Control; while a Skin is installed, the host should not be allowed to make modifications<br>
- Skins can monitor properties for changes but this should never lead to a direct observable change on the main control that a subsequent installed listener may observe; in other words, listener order should be irrelevant for what the Skin does in order to
share the listener infrastructure without interference. Skins are free to directly take action on the children (which they own exclusively), just not on the main control; such actions should instead be deferred, usually by requesting a layout (this is usually
already the case, but it is good to make this explicit so we can decide what a Skin is doing is a bug or not).<br>
- Behaviors can react to events at the lowest precedence, and exclusively only take action when receiving an event; this means that blocking all events will automatically mean the Behavior no longer does anything, but also that selectively blocking events allows
some control over Behaviors<br>
- Behaviors can co-modify properties on the Control, but this should be clearly documented; controls are free to restrict this set (ie. a Behavior has no business modifying the "wrapText" property, or things like layout properties -- most often they do their
work through pseudo class changes and modifying the value a control represents).</p><p class="ms-outlook-mobile-reference-message skipProofing">That should really be all that is needed for a functioning Skin/Behavior system; no need for root access.</p><p class="ms-outlook-mobile-reference-message skipProofing">Of course, root access to the Control is a ship that has sailed a long time ago; but that doesn't mean we can't introduce a client API for Skins/Behaviors. All that really takes is passing an object
to the Skin/Behavior when it is installed. This object is an interface with which the Skin/Behavior can do their work. Should they choose to not circumvent this API, and do all their work through this API, they can remove all their clean-up code, as the Control
can now do this automatically. This will greatly simplify skins, and remove a whole avenue of potential bugs.</p><p class="ms-outlook-mobile-reference-message skipProofing">All work done through this API can be monitored by the Control. The control can:<br>
- Track what is installed (for later clean-up)<br>
- Reject installation of listeners/handlers it doesn't want to expose<br>
- Ensure that event handlers are installed at lowest precedence. This can be kept internal, so many solutions are possible: separate lists, default event handlers (internal API), priorities, etc.</p><p class="ms-outlook-mobile-reference-message skipProofing">Everything you'd expect a host Control to be able to do, including forcefully removing all traces of a previously installed Skin, and disallowing it further access should it attempt to use the API
again after a new Skin is installed. That's however not a requirement; all we'd need is that interface, and encourage Skins/Behaviors to use it. Correctly behaved Skins/Behaviors then get all the benefits, and will stop interfering with user code. This means
of course modifications to existing skins, but it is mostly in their registration logic (which I think we modified like 5 times already).</p><p class="ms-outlook-mobile-reference-message skipProofing">The minimum API needed can be fairly small, and does not need to include accessors for every property and handler with some smart signatures. For example:</p><p class="ms-outlook-mobile-reference-message skipProofing"> <span style="font-family: Consolas; font-size: 11pt; background-color: rgb(255, 255, 255);">
<T, P </span><span style="font-family: Consolas; font-size: 11pt; color: rgb(0, 0, 160); background-color: rgb(255, 255, 255);"><b>extends</b></span><span style="font-family: Consolas; font-size: 11pt; background-color: rgb(255, 255, 255);"> ReadOnlyProperty<T>>
</span><span style="font-family: Consolas; font-size: 11pt; color: rgb(0, 0, 160); background-color: rgb(255, 255, 255);"><b>void</b></span><span style="font-family: Consolas; font-size: 11pt; background-color: rgb(255, 255, 255);"> addListener(Function<C,
P> supplier, Consumer<T> subscriber)</span></p><p class="ms-outlook-mobile-reference-message skipProofing">Allows installation of a listener by doing:</p><p class="ms-outlook-mobile-reference-message skipProofing"> <span style="font-family: Consolas; font-size: 11pt; background-color: rgb(255, 255, 255);">
api.addListener(Slider::minProperty, v -> { ... });</span><br>
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In this way we can isolate and track what Skins/Behaviors are doing, ensure they don't interfere with user operations on the Control and also ensure guaranteed clean-up (if they refrain from accessing the Control directly).</p><p class="ms-outlook-mobile-reference-message skipProofing">--John</p><p class="ms-outlook-mobile-reference-message skipProofing"><br>
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