[vJIYEv]

Checklist

• I have read and understand the contribution guide
• A CHANGELOG entry is included
• At least one test case is included for this feature or bug fix
• I have run automated testing and it is passed
• Documentation was added or is not needed
• This is an API breaking change

Issue Resolved / Feature Added

With scrollMode="native", holding a 5-way key (long press) on a horizontal/vertical VirtualList can leave the list scrolled short of the focused item. The focus reaches the first/last item but the list stops at an intermediate position, so the focused item is clipped or completely out of the viewport.

It happens when frames are delayed (e.g. a busy device right after boot), so it is intermittent.

Resolution

VirtualListBasic.animateScroll() started a new requestAnimationFrame loop on every call without stopping the ongoing one. During key repeat, several loops ran concurrently:

• each loop keeps scrolling toward its own (older) target, and
• when frames are delayed, a stale loop hits the 500ms timeout and its fallback node.scrollTo({left/top: <old target>, behavior: 'smooth'}) overrides the latest target.

Observed on a device (horizontal list, max scroll 745.5): scroll requests were 204 → 384.5 → 565 → 745.5, but stale fallbacks re-issued scrollTo(204), scrollTo(384.5), scrollTo(565) after the final request, and the list ended at 385/565.

The fix keeps a single animation loop and retargets it instead of starting another one:

• A new request only updates the target position and the timeout start time. A loop starts only when none is running, so the loop and its timeout fallback always use the latest target.
• The step per frame is scrollFactor × (number of items left to scroll). A single key press scrolls at the same speed as before. While a key is held, the speed keeps up with the focus, like the overlapping loops did before, without their stale targets.

The first revision of this PR cancelled the ongoing animation before starting a new one. Based on review feedback, it was changed because:

1. Long-press scrolling became too slow to keep up with the focus.
2. cancelScrollAnimation() set scrolling to false until the next frame, so onScrollEnd in ui/useScroll was no longer blocked and onScrollStop fired in the middle of a long-press scroll. With retargeting, the loop is never interrupted and scrolling stays true.

Additional Considerations

• Tests (VirtualList-native-specs.js): retargeting keeps scrolling true, reaching the latest target, timeout fallback to the latest target, timeout restart on a new request, and faster steps while several items are left. The retarget and speed tests fail with the first revision.
• Before/after comparison with a test app (horizontal VirtualList, 14 items, scrollMode="native", 4K viewport, long press with 50ms key repeat; frames delayed by deferring requestAnimationFrame):

Scenario	Before (5.6.0)	1st revision (cancel)	This PR (retarget)
Frame delay 50ms, long press →	FAIL (stops short)	PASS	PASS
Frame delay 50/100ms, long press ←	FAIL (stops short)	PASS	PASS
Max px of the focused item hidden while holding (delay 50ms, →)	~880	1123	821
onScrollStop while holding (no delay, → / ←)	0 / 1	3 / 4	0 / 1
40 items, 4s hold, no delay: focused index at release / onScrollStop while holding	31 / 0	24 / 15	31 / 0

• ui/Scroller animateScroll has the same pattern (no cancel before restart); not changed here.

Links

NXT-21053

Comments

Enact-DCO-1.0-Signed-off-by: Kyuman Lim (kyuman.lim@lge.com)

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 86.33%. Comparing base (6231f2e) to head (2d9b7ef).

Additional details and impacted files

@@                    Coverage Diff                    @@
##           release/5.6.x.develop    #3468      +/-   ##
=========================================================
+ Coverage                  86.31%   86.33%   +0.01%     
=========================================================
  Files                        156      156              
  Lines                       7615     7624       +9     
  Branches                    2013     2012       -1     
=========================================================
+ Hits                        6573     6582       +9     
  Misses                       831      831              
  Partials                     211      211              

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