Oh, sorry, I did not mean to ignore your comments. I should have
mentioned we are having a bi-annual "test sprint" and work exclusively
on the test suite. You made a lot of good comments that require some
thought and careful consideration, for which I simply had no spare CPU
cycles last week or this week. Sorry, will definitely respond in
detail early next week.
-andy
*From: *John Hendrikx <john.hendr...@gmail.com>
*Date: *Tuesday, September 17, 2024 at 23:05
*To: *Andy Goryachev <andy.goryac...@oracle.com>,
openjfx-dev@openjdk.org <openjfx-dev@openjdk.org>
*Subject: *Re: [External] : Re: Proposal: Focus Traversal API
Andy,
As you're not responding to any of the suggestions or any of my
questions, but are only re-iterating points that I believe are not
going to be a benefit to the long term viability of FX, I see no point
in continuing the discussion further.
--John
On 18/09/2024 01:09, Andy Goryachev wrote:
Dear John:
You do bring a lot of good points, no doubt. And I do agree with
a lot of the suggestion, but I still want to emphasize two points:
1. The backward compatibility should not be dismissed that
easily. There is a number of existing applications out there and
we do not want to break them. Whether the behavior is specified
or not is irrelevant, we do not want to cause mayhem from the
customers and developers alike whose keyboard navigation suddenly
changed.
2. I question the cost benefit analysis of the redesign idea.
While I agree with you that it might help with some unusual cases,
the overall benefit is rather limited. The benefit of the
proposed solution is, in my opinion, far greater: it allows for
custom traversal policies (a feature that has been requested
multiple times) and enables focus traversal from custom
components, something of a lesser value, but still important.
Exposing the existing APIs is a relatively cheap solution that
will give us two features at nearly zero cost. On the other hand,
I doubt that our team, or yourself, are willing commit substantial
development effort to redesign the thing to use events. Which
brings me to the choice I mentioned earlier: realistically, we
have a choice of providing two requested features soon, or never.
I would also encourage other members of the development community
to voice their opinion on the subject, perhaps there is something
else we can do to move forward.
Thank you
-andy
*From: *John Hendrikx <john.hendr...@gmail.com>
<mailto:john.hendr...@gmail.com>
*Date: *Saturday, September 14, 2024 at 09:41
*To: *Andy Goryachev <andy.goryac...@oracle.com>
<mailto:andy.goryac...@oracle.com>, openjfx-dev@openjdk.org
<openjfx-dev@openjdk.org> <mailto:openjfx-dev@openjdk.org>
*Subject: *[External] : Re: Proposal: Focus Traversal API
Hi Andy,
First let me say that when it comes to designing an API, you
really need to take the time to think the solution through. The
current internal solution was probably kept internal for exactly
that reason, insufficient time to work out the kinks and look into
alternatives.
An API is almost impossible to change later, so the general rule
is that if you're not sure about an API, then its better to have
no API. This is why I think it is important that we first look for
what the API should look like, then worry about how this can be
fitted onto JavaFX. Making concessions related to the current
implementation before having a clear idea of how the API should
preferably work is not part of that. You start making concessions
only when it turns out the preferred design would encounter
unresolvable problems in the current implementation.
Since I think there is very little public API related to focus
traversal, nor is there any specification of how it currently
works, I think we have a lot of room to maneuver. This is why I
think we should first reach a consensus on the API, then look how
it can be fitted on top of FX. Sometimes a well thought out API
also is a natural fit, and may be easier to migrate to than you think.
On 14/09/2024 00:17, Andy Goryachev wrote:
Dear John, Everyone:
Thank you for a thoughtful response! Some of the ideas you
described definitely deserve further consideration. If I were
to summarize:
1. move the focus traversal logic away from the components and
into the Scene
2. re-implement focus traversal through TraversalEvents rather
than responding directly to KeyEvents
3. (more) standard policies
4. using CSS
(there is of course more topics in your response, but let me
start with the 4 above)
#1
I generally like this idea. In some sense it is already how
things work internally, but without the ability to customize
that (i.e. by introducing custom traversal keys, or removing
existing ones). The downside is substantial: not only we'd
need to re-design the whole of the focus traversal, but also
rework the existing control's behaviors. Did I mention the
risk of regression, given the absence of comprehensive
behavioral tests?
There's two things here.
1. There is no need to re-design the whole focus traversal. The
old internal system can be gradually replaced (it works by
directly consuming KeyEvents after all).
2. Regression. When nothing is specified, and the fact that
controls **ought** to work like other common controls in different
UI toolkits, is it a regression when focus traversal works the
same as those other platforms, even if it may be a regression from
the point of view of FX? For example, a Spinner will currently
react to any mouse key, where as other common toolkits only react
to the left mouse button. Is it a regression if FX is adjusted to
also only react to the left mouse button? It's not specified
anywhere.
I think we have sufficient space to maneuver here as long as we
are not making focus traversal completely different from how it
commonly works in UI's.
Can there be regressions versus the current (unspecified)
implementation? Sure, there can be. Is that necessarily bad?
That depends. If the new focus traversal works like it does on
all other toolkits, then no, it is more of a bug fix. Did we
break something with the new implementation? That's always
possible, but will then be fixed as soon as it is reported.
#2
This may or may not be an integral part of #1. Potentially,
it allows for injection of events by the application code, as
well as simplifies creation of complex custom controls. The
latter becomes possible with the original proposal, so net
benefit is limited to the first part, I think.
I think TraversalEvents are quite central to making this an API
that will really stand the test of time. It leverages the
existing event system, giving you all the power that comes with
it. You did not answer my question about the TraversalEvents in
your design. Why are the Events when they can't be triggered,
filtered or consumed?
#3
One obvious possibility is to enable creation of a simple
policy based on a list of Nodes. I must mention one use case
that is impossible to cover with pre-defined policy is one
where navigation depends on some state. Such a policy must be
implemented programmatically. I think one property should be
sufficient - I am strongly against adding two properties here.
Programmatic escapes can always be achieved by responding directly
to a TraversalEvent. I think however this should be a rare case,
and standard policies should really cover almost all use cases.
It may be a gap that should be investigated, and the API adjusted
for (usually the "exceptions" are well worth looking into to see
if with a tweak they can't become "standard"). As for being
"strongly against" having two properties -- that's an odd stance
to take without motivating it. It could also be rolled into "one"
where the Policy is a record with the two values, but I think
we're getting ahead of ourselves here. First the API, then the
implementation.
I do think however there is great value in having the Logical and
Directional navigation split. Often you'll only want to replace
one of these with a custom policy (or a different standard
policy), so that the other navigation method can be used to escape
the control. For example, a Toolbar could be tabbed in an out of
(using Logical navigation) while the Directional navigation is
cyclic (and thus can't be used to escape the control's context).
#4
The idea of using CSS to specify traversal policy seems wrong
to me: the CSS defines the presentation aspects (styles)
rather than behavioral ones. I know it is possible to set
custom skins and the corresponding behavior via CSS, and we
know why (skins define the appearance), but we should not go
beyond that, in my opinion.
I see no problem styling such properties. They're FX properties,
and it would be very convenient to style them to globally alter
how focus works, instead of having to rely on, say, Builders or
Factories for controls where traversal policies can be applied.
There are also already properties that don't only influence the
look of controls. "-fx-skin" being the most obvious one, but
there is also "-fx-focus-traversable", "-fx-context-menu-enabled",
"-fx-block-increment", "-fx-unit-increment", "-fx-pannable",
"-fx-initial-delay", "-fx-repeat-delay", "-fx-collapsible",
"-fx-show-delay", "-fx-show-duration", "-fx-hide-delay", and
probably more. Aside from "-fx-skin" none of these properties
have a visual impact, but instead alter behavior.
Note: I'm not saying this needs to be there immediately. I just
want to make sure we're not closing off this direction, as again,
it would be a huge hassle to do this programmatically. In "code"
the only things I usually do on my controls are the following:
- I define the container hierarchy (VBox, HBox, which children go
where)
- I set a style name
- I set anything that unfortunately cannot be CSS styled (things
like ALWAYS, SOMETIMES, NEVER grow policies, Grid sizes, etc,
things that are clearly "visual" but still can't be styled).
All the rest I don't touch, or want to touch. Having to select a
traversal policy for every control of type X I create is just
cumbersome and unnecessary. There will be a call then to set this
"globally", and then there will be the question, do we make
something custom with many limitations because it doesn't fit our
conceptions of what (FX) CSS is for (ie, not style, but
only *visual* style) or do we just expose these properties as
Styleable leveraging an existing powerful system with almost zero
effort?
--
There is one more aspect of the problem that I think we should
consider. The current proposal does not change the
implementation in any material way, nor does it change the
behavior, thus can be done quickly. The benefit everyone gets
from it is ability to trigger focus traversal and to control
it via custom policies. Any other solution will require
resources and the bandwidth we currently don't have, which
means the /probability/ of it being added to FX is virtually
zero. Let me emphasize, I am not against attempting to
discuss or implement the best possible solution, but we should
be aware of the limitations of the reality we live in.
"Quickly" and API's are incompatible with each other. There is
nothing worse than exposing an API quickly, which then becomes a
burden on the system -- I think the current CSS API is a prime
example of where "quickly" has gone wrong, costing us tremendous
amounts of effort to make even minor changes to it.
I urge you to ignore the current implementation, think thoroughly
how (in an ideal world) you would want such an API to work (from a
user perspective, not from an implementor's perspective) and only
then see how this could be made to fit into JavaFX.
This is exactly what I did. I did not look at the implementation,
although I'm aware of some of it. I looked at how I as a user of
FX am building applications, the struggles I have with it
currently, (with controls for example "eating" KeyEvents), and how
I would like to be able to adjust focus traversal. Do I want to
respond to "KeyCode.LEFT" or do I want to respond to
"TraversalEvent.LEFT"? Do I also need to respond to
"KeyCode.NUM_PAD_LEFT"? These things should be abstracted, and
preferably I should just be able to choose from common navigation
standards. And when I do want to change such a standard, in 99%
of the cases that will be the case for all similar controls in my
application. How do I do such things currently if I want to
change something for all controls in my application? I use CSS.
Also I think this can be implemented gradually. Here's a
potential plan:
1. Have Scene listen to unused KeyEvents and translate them to
TraversalEvents
Benefit: gives custom controls a way to respond to keyboard based
navigation in a platform agnostic way; this probably already
removes the biggest roadblock for custom controls...
Public API: Limited to a new Event
2. Start converting existing controls to listen to TraversalEvent
instead of KeyEvent
This hits a lot of controls, but should be relatively easy to do,
and it can be all kept internal for now. It can be done in a few
batches.
Benefit: for each control converted, user can now programmatically
trigger focus changes, and by overriding things at Scene level can
completely change navigation keys
Public API: none
3. Implement a number of standard policies internally (OPEN,
CONFINED, CYCLIC, IGNORED)
Convert any controls that could use these as their default,
removing any custom logic if it happens to match one of the defaults.
Benefit: less code to maintain and debug, gives us experience with
which policies make sense and where the gaps are
Public API: none
Order: It is possible to do this before 2, and so some of the
control conversions could just consist of removing their custom
logic, and selecting a standard policy.
4. Expose policy property/properties on Parent
Any controls that are not using a custom policy anymore (of type
IGNORED) can now be user adjusted. We don't have to guarantee
that each policy makes sense for each control. Changing a default
IGNORED policy to a standard one will change the behavior (as
intended) but it need not be a "complete" behavior that users
like. This is not FX's problem, and can be improved upon later.
Benefit: users can now change policies on any existing control,
even ones with a custom policy; many of the controls may support a
switch between OPEN, CONFINED and CYCLIC out of the box.
Public API: new properties on Parent
5. Perhaps expose some helpful tools to calculate the "next" Node
for a given traversal option.
This can be done at any stage, and can be considered completely
separate. It is IMHO a relatively low priority need.
Benefit: less work for control implementors (although they could
just "copy" said code)
Public API: Maybe some methods in Node, or some kind of static helper.
6. CSS styleable properties
If we really want to give power to our users, and impress them
with a flexible focus traversal API, then make these properties
styleable.
Benefit: allow users to pick any control, and set is policy
globally or within a subset of controls (ie. dialogs, popups, etc).
Public API: Nothing in Java, but document as CSS properties
--John
Thank you,
-andy
*From: *openjfx-dev <openjfx-dev-r...@openjdk.org>
<mailto:openjfx-dev-r...@openjdk.org> on behalf of John
Hendrikx <john.hendr...@gmail.com>
<mailto:john.hendr...@gmail.com>
*Date: *Wednesday, September 11, 2024 at 19:05
*To: *openjfx-dev@openjdk.org <openjfx-dev@openjdk.org>
<mailto:openjfx-dev@openjdk.org>
*Subject: *Re: Proposal: Focus Traversal API
Hi Andy / List,
I've given this some thought first, without looking too much
at the proposal.
In my view, focus traversal should be implemented using
events, and FX should provide standard handling of these
events controlled with properties (potentially even CSS
stylable for easy mass changing of the default navigation policy).
## KeyEvent and TraversalEvent separation
I think the cleanest implementation would be to implement a
KeyEvent listener on Scene that takes any unused KeyEvents,
checks if they're considered navigation keys, and converts
these keys to a new type of event, the TraversalEvent. The
TraversalEvent is then fired at the original target. The
TraversalEvent is structured into Directional and Logical sub
types, and has leaf types UP/DOWN/LEFT/RIGHT and
NEXT/PREVIOUS. Scene is the logical place to handle this as
without a Scene there is no focus owner, and so there is no
point in doing focus traversal.
This separation of KeyEvents into TraversalEvents achieves the
following:
- User can decide to act on **any** key, even navigation keys,
without the system interfering by consuming keys early,
unexpectedly or even consuming these keys without doing
anything (sometimes keys get consumed that don't actually
change focus...). The navigation keys have many possible dual
purposes, and robbing the user of the opportunity to use them
due to an overzealous component interpreting them as traversal
keys is very annoying. Dual purposes include for example
cursor control in TextField/TextArea, Scrollbars, etc. The
user should have the same control here as these FX controls have.
- Scene is interpreting the KeyEvents, and this interpretation
is now controllable. If I want a Toolbar (or the whole
application) to react to WASD navigation keys, then installing
a KeyEvent handler at Scene level or at any intermediate
Parent level that converts WASD to UP/LEFT/DOWN/RIGHT
Traversal events would affect this change easily.
- The separation also allows to block Focus Traversal only,
without blocking the actual Keys involved. If I want to stop a
Toolbar from reacting to LEFT/RIGHT, but I need those keys
higher up in the hierarchy, then I'm screwed. With the
separation, the key events are unaffected, and I can block
Toolbars from reacting specifically to traversal events only.
## Traversal Policy Properties on Parent
I think FX should provide several policies out of the box,
based on common navigation patterns. The goal here is to have
policies in place that cover all use cases in current FX
provided controls. This will provide a good base that will
cover probably all realistic work loads that custom controls
may have. The goal is not to support every esoteric form of
navigation, instead an escape hatch will be provided in the
form of disabling the standard navigation.
In order to achieve this, I think Parent should get two new
properties, which control how it will react to Directional and
Logical navigation. These will have default values that allow
navigation to flow from Node to Node within a Parent and from
Parent to its Parent when navigation options in a chosen
direction are exhausted within a Parent. Custom controls like
Combo boxes, Toolbars, Button groups, etc, can change the
default provided by a Parent (similar to how some controls
change the mouse transparent flag default).
These two properties should cover all realistic needs, and
IMHO should be considered to be CSS stylable in the future to
allow easy changing of default policies of controls (ie. want
all Toolbars to react differently to navigation keys, then
just style the appropriate property for all toolbars in one go).
Parent will use these properties to install an event handler
that reacts to TraversalEvents (not KeyEvents). This handler
can be fully disabled, or overridden (using setOnTraversalEvent).
- logicalTraversalPolicy
- directionalTraversalPolicy
The properties can be set with a value from a TraversalPolicy
enum. I would suggest the following options:
- OPEN
This policy should be the default policy for all Parents. It
will act and consume a given TraversalEvent only when there is
a suitable target within its hierarchy. If there is no
suitable target, or the target would remain unchanged, the
event is NOT consumed and left to bubble up, allowing its
parent(s) to act on it instead.
- CONFINED
This policy consumes all TraversalEvents, regardless of
whether there is something to navigate to or not. This policy
is suitable for controls that have some kind of substructure
that we don't want to accidentally exit with either
Directional or Logical navigation. In most cases, you only
want to set one of the properties to CONFINED as otherwise
there would be no keyboard supported way to exit your
control. This is a suitable policy for say button groups,
toolbars, comboboxes, etc.
- CYCLIC
Similar to CONFINED but instead of stopping navigation at the
controls logical boundaries, the navigation wraps around to
the logical start. For example, when were positioned on the
right most button in a button group, pressing RIGHT again
would navigate to the left most button.
- IGNORED
This is similar to the mouseTransparent property, and
basically leaves the TraversalEvent to bubble up. This policy
allows you to completely disable directional and/or logical
navigation for a control. Useful if you want to install your
own handler (the escape hatch) but still want to keep either
the default directional or logical navigation.
Possible other options for this enum could include a version
that consumes all TraversalEvents (BLOCK) but I don't see a
use for it at the moment. There may also be variants of
CONFINED and CYCLIC that make an exception for cases where
there is only a single choice available. A ButtonGroup for
example may want to react differently depending on whether it
has 0, 1 or more buttons. Whether these should be enshrined
with a custom enum value, or perhaps a flag, or just left up
to a custom implementation is something we'd need to decide still.
## Use Cases
1) User wants to change the behavior of a control from its
default to something else (ie. a Control that is CYCLIC can be
changed to OPEN or CONFINED)
Just call the setters with the appropriate preferred policy.
This could be done in CSS for maximum convenience to enable a
global change of all similar controls.
2) User wants to act on Traversal events that the standard
policy leaves to bubble up
Just install a Traversal event handler either on the control
or on its parent (depending on their needs). A potential
action to an unused Traversal event could be to close a
Dialog/Toast popup, or a custom behavior like selecting the
first/last item or next/previous row (ie. if I press "RIGHT"
and there is no further right item, a user could decide to
have this select the first item again in the current Row or
the first item in the **next** Row).
3) User wants to do crazy custom navigation
Set both policies to IGNORED, then install your own event
handler (or use the setOnTraversalHandler to completely
override the handler). Now react on the Traversal events,
consuming them at will and changing focus to whatever control
you desire.
4) User wants to change what keys are considered navigation keys
Install event handler on Scene (or any intermediate Parent)
for KeyEvents, interpret WASD keys as UP/LEFT/DOWN/RIGHT and
sent out a corresponding Traversal event
5) User wants to use keys that are considered navigation keys
for their own purposes
Just install a KeyEvent handler as usual, without having to
worry that Skins/Controls eat these events before you can get
to them
6) User wants to stop a control from reacting to traversal
events, without filtering navigation keys completely
With the separation of unconsumed KeyEvents into
TraversalEvents, a user can now block only the latter to
achieve this goal without having to blanket block certain
KeyEvents.
-----
About the Proposal:
I think the Goals are fine as stated, although I think we
differ on what the Traversal events signify.
I think CSS support should be considered a possible future
goal. The proposal should therefore take into account that we
may want to offer this in the future.
Motivation looks okay.
> The focus traversal is provided by the FocusTraversal class
which offers static methods for traversing focus in various
directions, determined by the TraversalDirection enum.
I think these methods don't need to be exposed with a good
selection of standard TraversalPolicy options. After all,
there are only so many ways that you can do a sensible
navigation action without confusing the user, and therefore I
think these policy options will cover 99% of the use cases
already. For the left over 1% we could **consider** providing
these focus traversal functions as a separate public API, but
I would have them return the Node they would suggest, and
leave the final decision to call requestFocus up to the
caller. Initially however I think there is already more than
enough power for custom implementations to listen to Traversal
events and do their own custom navigation. If it is not
similar to one of the standard navigation options, the
traverseUp/Down functions won't be of much use then anyway.
About your typical example:
Node from = ...
switch (((KeyEvent)event).getCode()) {
case UP:
FocusTraversal.traverse(from, TraversalDirection.UP,
TraversalMethod.KEY);
event.consume();
break;
case DOWN:
// or use the convenience method
FocusTraversal.traverseDown(from);
event.consume();
break;
}
I think this is not a good way to deal with events.
1) The event is consumed regardless of the outcome of
traverse. What if focus did not change? Should the event be
consumed?
2) This is consuming KeyEvents directly, robbing the user of
the opportunity to act on keys considered "special" by FX.
3) This code is not only consuming KeyEvents directly, but
also deciding what keys are navigation keys.
So I think this example code should be different. However,
first I expect that in most cases, configuring a different
traversal policy on your Parent subclass will already be
sufficient in almost all cases (especially if we look at FX
current controls and see if the suggested policies would cover
those use cases). So this code will almost never be needed.
However, in the event that you need something even more
specific, you may consider handling Traversal events directly.
In which case the code should IMHO look something like this:
Node from = ...
Node result = switch(traversalEvent.getEventType()) {
case TraversalEvent.UP -> FocusTraversals.findUp(from);
case TraversalEvent.DOWN -> FocusTraversals.findDown(from);
// etc
}
if (result != null) {
result.requestFocus();
traversalEvent.consume();
}
Note that the above code leaves the final decision to call
requestFocus up to the caller. It also allows the caller to
distinguish between the case where there is no suitable Node
in the indicated direction and act accordingly.
This allows it to NOT consume the event if it prefers its
Parent to handle it (if the control doesn't want CYCLIC or
CONFINED style navigation). It also allows it to further
scrutinize the suggested Node, and if it decides it does not
like it (due to some property or CSS style or whatever) it may
follow up with another findXXX call or some other option to
pick the Node it wants. It also allows (in the case of no
Node being found) to pick its own preferred Node in those
cases. In other words, it is just far more flexible.
I'm not sure yet where to place these static helper methods
(if we decide to expose them at all initially), or even if
they should be static. Given that its first parameter is
always a Node, a non-static location for them could simply be
on Node itself, in which case the calling convention would
become "Node result = from.findTraversableUp()" (suggested
name only)
> Focus traversals generate a new type of event, encapsulated
by the class TraversalEvent which extends javafx.event.Event,
using the event type TraversalEvent.NODE_TRAVERSED.
What is the point of this event? If you want to know that
focus changed, you can add a listener to
Scene.focusOwnerProperty. What does it mean if I filter this
event? What if I consume it? I don't think this should be an
event at all, unless implemented as I suggested above, where
consuming/filtering/bubbling can be used to control how
controls will react to navigation events.
--John
On 03/09/2024 21:33, Andy Goryachev wrote:
Dear fellow developers:
I'd like to propose the public focus traversal API:
https://github.com/andy-goryachev-oracle/Test/blob/main/doc/FocusTraversal/FocusTraversal.md
<https://urldefense.com/v3/__https:/github.com/andy-goryachev-oracle/Test/blob/main/doc/FocusTraversal/FocusTraversal.md__;!!ACWV5N9M2RV99hQ!LnjDXwUbbEymf9b1gkZFia8vuewsVJy6_49It-IKw66U9mS78PjdIPotBpc7AXlSfY7N5xcRXsmcPQhOzavk4z9VkPv-$>
Draft PR:
https://github.com/openjdk/jfx/pull/1555
<https://urldefense.com/v3/__https:/github.com/openjdk/jfx/pull/1555__;!!ACWV5N9M2RV99hQ!LnjDXwUbbEymf9b1gkZFia8vuewsVJy6_49It-IKw66U9mS78PjdIPotBpc7AXlSfY7N5xcRXsmcPQhOzavk49fH_P2p$>
Your comments and suggestions will be warmly accepted and
appreciated.
Thank you
-andy
