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>
*Date: *Saturday, September 14, 2024 at 09:41
*To: *Andy Goryachev <andy.goryac...@oracle.com>,
openjfx-dev@openjdk.org <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
