[External] : Re: Proof of concept pull request for Behavior API (PR 1265)

[John Hendrikx]

The normal procedure I think is also to first provide a JEP for review, 
before starting on the implementation...

Given the doubts raised, feedback given and potential alternatives 
proposed, I don't see why you are still moving forward with your own 
proposal. The critiques I've given have been mostly hand waved with 
arguments that have no place in JEP evaluation (time restrictions, 
existing code already works this way, false equivalency with MVC 
pattern), and therefore have IMHO not been taken serious at all.

This leaves me in the position of putting in a lot of work that will 
essentially be ignored as I feel an (internal) decision has already been 
reached, regardless of the feedback on the mailinglist.

The (partial) proposal I've made, and also simpler proposals so that 3rd 
parties could do a keybinding implementation, should be sufficient to 
reconsider the current proposal that is being moved forward.

I'll reiterate my problems with your proposal:

- Introduces a lot of API for what is essentially the configuration of 
internal event handlers
- The proposed API partially overlaps with the existing event handler 
API, meaning that some keys could be changed with just event handlers, 
while some can only be changed with the BaseBehavior API; it also 
provides for creating new functions and assigning them to keys, 
essentially a new (very limited) API for what was already possible in 
the much more flexible event handling API
- Introduces the term "Behavior" in public API without clearly 
specifying what that is, nor showing enough forethought that may make it 
possible in the future to have public Behaviors
- Introduces the term "InputMap" in public API, which is just an 
implementation detail of the internal event handlers
- Doesn't address the real issue IMHO, which is that JavaFX 
Skins/Behaviors install their Event Handlers directly on Controls, 
mixing them with user event handlers leading to all sorts of 
unpredictable behavior due to call order and internal handlers 
essentially stealing and consuming events before the user has a chance 
to look at them (and thus blocking any 3rd party key alterations) which 
leads to the (false) need to change key bindings and Behaviors directly...

So if you want me to work on such a proposal, fully fleshing it out, I 
would like to know if it will be given consideration. I would also like 
some more feedback on what is already there, as I think it is sufficient 
to decide if a full proposal is worth it or not.

My proposals in short:

1.

- Fix the issues with Events being stolen before users can get a them
     - Users should be able to have priority on Events, Michael Strauss 
already has a PR that fixes the issue in part
     - Events should not be consumed when not used (navigation does 
this) as this precludes the user being able to change their meaning
     - Even better would be if internal event handlers were isolated and 
did not mix themselves with user event handlers at all

The above can be done separately, and should already make it possible to 
do a lot of things that were close to impossible before when it comes to 
changing key handling, but certainly not everything.

- Building on top of the improved event handling system, introduce a 
flag to indicate an event is not to be consumed by internal event handlers

These two together can form the basis for a 3rd party Behavior 
implementation as standard behavior can be prevented from occurring.  It 
leaves platform dependent behavior to be addressed by such a 3rd party / 
user implementation as it is a very low level API.  Any key remapping 
logic would be provided by the 3rd party API.

2.

I also have a more fleshed out alternative proposal that attempts to 
introduce Behaviors into JavaFX as a first class concept, instead of a 
potential 3rd party add-on.  Recap:

- Introduce a Behavior interface with a single method "install" to be 
called by a Control
- The "install" method is provided a context object, BehaviorContext.  
This indirects any changes the Behavior can make to a Control, so the 
Control is fully aware of all changes and can uninstall them without 
further co-operation from the behavior.
- The BehaviorContext provides low level functions to add/remove event 
handlers and listeners, but can also provide higher level functions (in 
perhap a later PR) to allow for some kind of control provided input map 
system
- Standard Behaviors can be made public and can be easily subclassed or 
composed as they need not have any state.  State is tracked inside the 
behavorial installed listeners and handlers themselves (either directly 
or by referring to some shared State object).
- Clear separation of concerns; Behaviors, a resuable concept that can 
be applied to a control; BehaviorContext, manages behavior lifecycle by 
abstracting away direct Control access; behavior state management left 
up to the implementation and created (on demand and as needed) when 
"install" is called.
- Indirection from key mapping to semantic meaning is provided by 
introducing control specific events. These semantic events can be 
handled, filtered and consumed like all other events, allowing for 
changing/remapping/blocking or ignoring; this part can be left out from 
an initial implementation to further evaluate how such events might 
interact with Skins that need specific events (there is nothing stopping 
us from having some of these semantic events be handled by the Control 
directly, and some by the specific needs of the Skin)

To get at the internal key mappings, you'd need to subclass or compose a 
Behavior.  The Behaviors are setup to allow this easily.  To modify the 
bindings of a Control, one would install such a modified Behavior as a 
whole; overkill perhaps for one binding change, but convenient when 
multiple bindings are changed, and reusable accross controls (the 
Behavior only need to be created once).

The proposal also includes an indirection between Key/Mouse event and 
its semantic meaning.  This is achieved by firing higher level more 
meaningful events, but that's not the only option; it could also be done 
with overridable methods on the Behavior, or a behavior specific 
interface if the Event based proposal is seen as too audacious.

This proposal advocates a clear seperation of the Behavior from the 
Skin, essentially making them Controller and View, where the View has no 
knowledge of the Controller. I see no reason why this wouldn't be 
possible, given that it is a standard pattern.  That existing controls 
may be difficult to untangle is IMHO irrelevant, especially when this 
can be done one at a time.  I realize that Controllers (Behaviors) may 
have functions that are sort of View (Skin) specific; this is not an 
issue, as it should be fine to trigger a behavior without it being 
consumed; unconsumed behaviorial events just bubble up.  This allows 
Behaviors to have events specific to a Skin without them interfering if 
they're unused by an alternative Skin.  An alternative Skin that also 
needs new behavior will also need to create a new behavior to go along 
with it (or when paired with the standard one, accept that those new 
behaviors won't be triggered).

Thanks for reading.

--John



On 26/10/2023 00:59, Andy Goryachev wrote:
>
> Dear John:
>
> It is difficult to review the alternative proposal for a number of 
> reasons.  A prototype is a good start, but for any proposal to go 
> forward we need a bit more work.  Let me enumerate the steps that we 
> expect:
>
> 1. Provide an overview of the proposal following a JEP outline:
>
> *Summary*
>
> *Goals*
>
> *Non-Goals*
>
> *Motivation*
>
> *Description*
>
> *Alternatives*
>
> *Risks and Assumptions*
>
> *Dependencies*
>
> 2. A draft PR that provides a proof of concept, using, in this case, a 
> few complex controls like TextArea, TableView, ComboBox.
>
> 3. Address the question raised earlier, perhaps by providing code 
> examples (pseudo code is acceptable, I think).
>
> More specifically, I’d like to know how the following concerns will be 
> addressed by the new proposal:
>
> Q1. Changing an existing key binding from one key combination to another.
>
> Q2. Remapping an existing key binding to a different function.
>
> Q3. Unmapping an existing key binding.
>
> Q4. Adding a new key binding mapped to a new function.
>
> Q5. (Q1...Q4) scenarios, at run time.
>
> Q6. How the set behavior handles a change from the default skin to a 
> custom skin with some visual elements that expects input removed, and 
> some added.
>
> Q7. Once the key binding has been modified, is it possible to invoke 
> the default functionality?
>
> Q8. How are the platform-specific key bindings created?
>
> Q9. How are the skin-specific (see Q6) handlers removed when changing 
> the skins?
>
> Q10. When a key press happens, does it cause a linear search or a map 
> lookup?
>
> Thank you
>
> -andy
>
> *From: *John Hendrikx <john.hendrikx at gmail.com>
> *Date: *Tuesday, October 24, 2023 at 04:58
> *To: *Andy Goryachev <andy.goryachev at oracle.com>, 
> openjfx-dev at openjdk.org <openjfx-dev at openjdk.org>
> *Subject: *Re: [External] : Re: Proof of concept pull request for 
> Behavior API (PR 1265)
>
> On 23/10/2023 23:57, Andy Goryachev wrote:
>
>     You'd create a new class, `MyBehavior`,
>
>     By “customizing” I also mean at run time.  Creating new classes
>     wouldn’t work.
>
> This would also work at runtime, as the class you create can be 
> instantiated with parameters that control its key binding behavior.  
> Even though the standard Behaviors should probably be singletons (so 
> they can be reused and composed) or have public well documented 
> constructors, a custom behavior created by the user has no such 
> re-usability restrictions.
>
>     coupling
>
>     I don’t think it is our choice - it is up to the skin designed. 
>     If they add a node that needs to take input, or if the behavior is
>     drastically different, it is almost impossible to create a common
>     interface.  So skin and behaviors are coupled, besides we have to
>     design for the worst case (of a totally different skin).  The
>     division between S and B comes mostly from the division between V
>     and C in MVC.  From a distance, the user does not see it at all -
>     all they see is a control.
>
> JavaFX is not doing MVC.
>
> In MVC, the 3 components are not entangled; Model refers View, 
> Controller refers View and Model, View refers nothing; in JavaFX the 
> View (Skin) creates the Controller (Behavior); the View especially 
> normally can be created without any dependencies, and can be tested as 
> such; with Skins being tightly coupled to both Behaviors and Controls, 
> that doesn't even come close.
>
> For it to be MVC you'd need to:
>
> - Remove reference from Skin to Control
> - Do not let Skins create Behaviors
> - Instantation order should be, create a Skin first (with no Control 
> reference), then create the Control (with Skin as parameter or 
> setter), then create a Behavior (with Control as parameter, and one or 
> more Views (Skins))
>
> What JavaFX is exactly,  I don't know. It doesn't follow MVC (even 
> though it claims to) because in the current setup the Skin is both V 
> and C; that's not MVC.  At most it is MS (Model Skin), and so there is 
> no reason to expose anything beyond the Skin then, as that would just 
> be pretending to be something that it is not.
>
>     This suggest another metric at judging the usefulness of a design
>     - how easy it is to understand and perform 80% of most common tasks.
>
> Now that I explained how key remappings would work, I don't see how 
> this would disqualify the alternative proposal.
>
>     There are more interesting ideas at the end of the message I am
>     replying to - fxml, css, global changes - these go far beyond the
>     simple input map improvement.  I did mention this already, but
>     neither open source community, nor my employer might have the
>     resources to make such drastic changes.
>
> I didn't mention FXML, but yes, I gave some other things to think 
> about.  As for how drastic any of those are, that remains to be seen.  
> Certainly the global changes would not be that hard at all.  The CSS 
> proposal would need some research if there is some will to go there; 
> it assumes that the information needed can be transported in a 
> reasonable manner to the key binding system using the existing CSS 
> infrastructure.
>
>     So we have to be realistic, I think.  We are travelling to a
>     different planet in a small spaceship and we only have so much
>     material and oxygen to play with.  A simple improvement that helps
>     80% of use cases might be better than a major redesign (I still
>     think the event proposal involves major redesign).
>
> I think that if that's the case that we'd better focus on making it 
> possible for 3rd parties to deliver these features, and do the 
> simplest thing that would allow them to do so. That would be 
> prioritized event handlers (so a 3rd party can always intercept before 
> the Skin/Behavior gets to it) + a flag to skip system event handlers 
> (ala consumed) to allow bubbling up.
>
> On top of that any key remapping or behavior change system can be 
> constructed already.
>
> --John
>
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