[ddx533534]

Summary:

When a parent intercepts an already-started ScrollView drag, Android delivers ACTION_CANCEL. The current ACTION_UP-only condition skips END_DRAG, the native gesture end notification, resetting dragging, and post-touch cleanup.

Handle ACTION_CANCEL alongside ACTION_UP in ReactScrollView, ReactHorizontalScrollView, and ReactNestedScrollView. Cancellation preserves the tracked velocity and uses the existing post-touch settling pipeline, including configured momentum events and page alignment. The nested component was regenerated with its source generator.

Changelog:

[ANDROID] [FIXED] - Finish interrupted ScrollView drags when receiving ACTION_CANCEL.

Test Plan:

Current upstream source: 12 Robolectric cases passed, 0 failures and 0 skipped, on c7429b0 plus this patch. Each vertical, horizontal, and nested component is covered for cancellation ending a drag exactly once, cancellation without dragging, normal UP behavior, and post-touch cleanup notifying native scroll-ended listeners and disabling the FPS listener.

./gradlew :packages:react-native:ReactAndroid:testDebugUnitTest --tests com.facebook.react.views.scroll.ReactScrollViewTouchCancelTest -PreactNativeArchitectures=arm64-v8a -PndkVersion=29.0.13113456 -Preact.internal.useHermesStable=true -x :packages:react-native:ReactAndroid:prepareNative3pDependencies -x :packages:react-native:ReactAndroid:preparePrefab

The JVM run compiled RN Kotlin/Java from source; the excluded tasks prepare C++ headers. git diff --check, formatting of the new Kotlin test, and the nested-scroll generator --verify check also passed.

Android emulator: Built before/after native harness APKs using the real RN 0.83.10 vertical ReactScrollView on Android 16 ARM64. The RN source differs only in the terminal-action condition. After RN emits BEGIN_DRAG, the parent intercepts the stream and Android itself delivers CANCEL.

After parent interception	Before	After
BEGIN_DRAG / END_DRAG	1 / 0	1 / 1
Native gesture started / ended	1 / 0	1 / 1
dragging	true	false
FPS listener after settling	enabled	disabled
Momentum begin / end (enabled)	0 / 0	1 / 1

All 12 before/after emulator scenarios matched expectations: drag + cancel, drag + up, cancel without dragging, repeated cancellation, paging-enabled cancellation, and cancellation with momentum events disabled. Paging-enabled cancellation settled with balanced momentum events.

The recordings demonstrate native event emission and cleanup on RN 0.83.10; the harness does not run a JS VM. Current-source coverage for horizontal/nested components comes from the Robolectric tests above.

Reproduction evidence

Before the fix: END_DRAG=0, dragging=true, FPS listener remains enabled after cancellation.

before.mp4

After the fix: END_DRAG=1, dragging=false, native gesture end and post-touch cleanup complete.

after.mp4

Download the standalone native reproducer, recordings, and emulator results. See its README for setup and the exact verification scope.

[ddx533534]

Reproduction recordings and standalone native harness:

before.mp4

after.mp4

rn-scroll-cancel-reproducer.zip

[meta-codesync]

@javache has imported this pull request. If you are a Meta employee, you can view this in D126637111.