How navigation currently works in FX, and an enhancement proposal

[John Hendrikx]

This should certainly also become possible at some point.  There already 
is internal API to find the next/previous or left/right Node, it is more 
a question how to expose this as an API at this point.

For this specific case, you'd probably want to change focus in an 
ActionEvent, or possibly a KeyEvent handler that looks for ENTER.

Then in the handler you'd probably just want to ask Scene to move focus 
to the logical next Node.  When in an event handler, that could be 
something like:

       oneOfMyNodes.getScene().focusNext();

or:

       oneOfMyNodes.getScene().focus(Direction.NEXT);

 From what I can see, these methods would be trivial to add to Scene, as 
all the traversal methods are already present there.  I also think that 
it would be the correct place to have them, as there is no focus without 
a Scene and Scene already has the focusOwner property.

Currently this all is already possible for the user, but you'd need to 
build your own util that finds the next Node (there are some simple 
rules for this, like finding the current child index in the parent, 
going up the stack of parents when on the last child, etc... I think I 
may have it somewhere in a utility already :))

--John


On 19/09/2024 20:30, Chuck Davis wrote:
> Focus traversal in JavaFX is one of the two things I miss most about 
> Swing.  With Swing we could access the policy and move to the next or 
> previous object programmatically -- a feature that is sadly lacking in 
> FX.  For those of us old enough to remember the good old days of 
> character interfaces, hitting the enter key was the way to move to the 
> next input field.  I still maintain that feature but I've had to write 
> all the code myself and for each field it has to be hard coded -- a 
> real nuisance and totally unnecessary if we could access the 
> TraversalPolicy and call next() or previous() like we did in Swing.
>
> For example, place characters in a TextField and hit the enter key to 
> trigger an event.  Execute the method to process the verification, 
> conversion, formatting and then TraversalPolicy.next() places focus on 
> the next input field -- good old efficient input and finger action.  
> No unnecessary and inefficient hand movements.
>
> My $.02 on this whole discussion in this and associated threads 
> regarding addressing the FX TraversalPolicy.
>
> On Thu, Sep 19, 2024 at 8:39 AM John Hendrikx 
> <john.hendrikx at gmail.com> wrote:
>
>     I've been looking into how exactly navigation keys are being used
>     in FX,
>     and who is responsible for handling them:
>
>     - Controls can choose to install navigational keys directly in their
>     input map (using FocusTraversalInputMap::getFocusTraversalMappings)
>     - Controls can choose to do nothing and leave navigation keys to
>     bubble
>     up to Scene, at which point Scene will act on any unconsumed
>     navigation
>     keys (in the same was as the traversal mappings would)
>
>     Scene basically is capable of almost all navigation you could
>     possibly
>     want out of the box.  Any control that does not install navigation
>     keys,
>     and leaves said keys to bubble up gets navigation for **free**. 
>     This is
>     almost all controls in JavaFX, and it makes sense as Controls
>     should not
>     care about navigation, they should only care about key presses that
>     affect them directly.  Navigation should be a concern somewhere
>     higher
>     up in the hierarchy.
>
>     So why do some controls install their own navigation keys?
>
>     There are two answers:
>
>     1. For some controls, navigation is conditional. A Spinner only
>     allows
>     directional navigation for the left/right keys, or up/down keys
>     depending on its orientation.
>     2. There is an unfortunate choice in ScrollPane that consumes
>     directional keys for scrolling purposes, and so if such keys were
>     left
>     to bubble up, they would not end up at Scene.  Any control supporting
>     directional navigation therefore must **specifically** install these
>     bindings directly, even though navigation is not their concern (a
>     Button
>     cares about being pressed, not about activating unrelated controls
>     nearby).
>
>     The ScrollPane eating directional keys is an odd choice. In order
>     for it
>     to do so one of the following must be true:
>
>     - A control inside it has focus that should act on directional
>     navigation, but forgot to install navigation bindings (a custom
>     control).  Such a control would work perfectly when not part of a
>     ScrollPane (as Scene would then handle directional navigation), but
>     break when placed inside it.  Note that all JavaFX controls do this
>     "properly".  I couldn't find any controls that would leave
>     directional
>     keys to bubble up for a ScrollPane to consume.
>
>     - The ScrollPane itself has focus; this can only happen when directly
>     selected with the mouse (or focus traversable is set to true) and no
>     specific control inside the pane was selected.  The ScrollPane
>     receives
>     the ":focused" style, clearly indicating that it is the target for
>     keyboard events to the user.
>
>     In short, ScrollPane is making navigation a lot more complex
>     within FX
>     than it needs to be.  Especially custom controls that do not have
>     access
>     (currently) to install navigational bindings will suffer from
>     this, and
>     will have to resort to their own navigation implementation for
>     directional keys when placed inside a ScrollPane.
>
>     # Proposal
>
>     I think ScrollPane violates what I think should be a fundamental
>     rule.
>     Keys should only be consumed by what the user perceives as the
>     focused
>     control (ie. the one outlined with a highlighted border), with the
>     only
>     exceptions being short cuts (from a menu) or mnemonics. Containers
>     such
>     controls happen to be placed in should NOT consume key events -- the
>     container is not the control with the focus, and so would confuse the
>     user.  Only ScrollPane is violating this currently.  Note that if the
>     ScrollPane has focus itself (and it has the :focused highlight)
>     then it
>     is perfectly fine and expected for it to consume keys as much as
>     it wants.
>
>     This is why I think we should modify ScrollPane to not consume the
>     directional keys, unless it specifically has the focus.  All other
>     controls can then remove their navigational bindings and leave
>     them to
>     bubble up to Scene, cleaning up their behaviors so they can focus on
>     other concerns.  Custom controls would no longer need to install
>     navigational bindings either, and would not need to worry about being
>     placed inside a ScrollPane and having their directional navigation
>     broken.
>
>     Optional, but recommended, controls like Spinner should only act
>     on the
>     directional keys intended for them, and leave the ones they can't
>     use to
>     bubble up.  So a vertical spinner would consume up/down for
>     changing the
>     spinner value, but would leave left/right untouched for Scene to
>     handle.  Controls that install a full set of navigational keys (like
>     Button, ListView and TitledPane) don't need to do so anymore.
>
>     I think I will file a ticket for this soon, but I'm curious what
>     others
>     think of this analysis.
>
>     Note that by solving this problem, the need to make navigation
>     functionality available to custom controls severely diminishes as one
>     can simple leave the KeyEvents responsible for standard navigation to
>     bubble up (recommended as this may be different for each platform).
>
>     --John
>
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