Prioritized event handlers

[Martin Fox]

I understand John’s point: you want all the user installed filters and handlers across all levels to be processed before switching to system level processing. I also understand this prioritization proposal is designed to push our existing set of system handlers to a separate phase. But is that all we’re talking about here? I need some clarification.

Within a given control the order of event processing gets involved. If a Control is subclassed the subclass should get first shot at the event. The same is true for Behaviors and Skins. Beyond that I’m still not clear if the behavior or skin should get the event first or if the skin should get it via the behavior or the other way around. In any case, you’ve got the control, the behavior, the skin, and all of their subclasses trying to sort out the execution order.

Based on this discussion (and I might be mistaken on this) it sounds like you're trying to handle all this using this proposal, namely registering event handlers with a prioritization scheme. Wouldn’t it be easier to just grab the event and pass it around using Java method calls? Perhaps the call is handleEvent(). A control implements handleEvent() by passing the event off to the behavior’s handleEvent() which passes it off to the skin’s handleEvent(). The skin sends it up the superclass chain by calling super.handleEvent(), etc. so on.

This would make for an easy sell to outside developers. We can tell them that if they subclass a Control and implement handleEvent() they will get events first during the system phase. The same is true if they subclass a behavior or skin. They don’t need to buy into or even see a complicated event prioritization scheme to get exactly what they expect, namely first access to events.

But, again, maybe I’m off base here. Let me know.

Martin

> On Oct 30, 2023, at 12:53 PM, Andy Goryachev <andy.goryachev at oracle.com> wrote:
> 
> Dear Michael:
>  
> Thank you, this is very helpful.
>  
> Questions/Comments:
>  
> 1. Does this proposal changes the way events are dispatched with respect to priority?  In other words, does it first go through the list of all handlers registred on the leaf Node (high priority first, then lower, then lowest), then bubble up?  Or do they propagate upwards looking for high priority handlers first, then the process restarts for lower priorities, as I saw in some previous emails?  (I could be mistaken)
>  
> 2. Do you propose to abort event dispatching immediately after the event is consumed?  This probably should be mentioned earlier in the Motivation (the problem statement) section.
>  
> 3. I wonder if three priority levels are sufficient.  Let me explain.  We have two possible actors who can register an event listener: the application code and the FX (or, rather more specifically, the skin and its behavior, whatever that might be).
>  
> Application code might want to add handlers at three possible priorities:
>  
> App handler must always be called before any fx handler
> App hander does not care
> App handler must always be called after any fx handlers
>  
> For fx/skin handlers we might have fewer levels:
>  
> Skin handler does not care
> Skin handler must be called after all other skin handlers
>  
> This situation maps to 5 priorities and 4 effective levels (or 5).
>  
> We should also mention the fact that when any actor adds two or more handlers for the same event with the same priority, they get invoked in the order added.
>  
> Would you agree, or am I missing some critical aspect of the proposed solution?
>  
> Thank you
> -andy
>  
>  
>  
>  
>  
> From: openjfx-dev <openjfx-dev-retn at openjdk.org> on behalf of Michael Strauß <michaelstrau2 at gmail.com>
> Date: Friday, October 27, 2023 at 19:41
> To: openjfx-dev <openjfx-dev at openjdk.org>
> Subject: Re: Prioritized event handlers
> 
> Here is the proposal:
> https://gist.github.com/mstr2/4bde9c97dcf608a0501030ade1ae7dc1
> 
> Comments are welcome.
> 
> 
> On Fri, Oct 27, 2023 at 8:21 PM Andy Goryachev
> <andy.goryachev at oracle.com> wrote:
> >
> > Would it be possible to create a proposal in the JEP format outlining the proposed public API?
> >
> >
> >
> > Thank you
> >
> > -andy

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