[iOS] Keep NativeViewGestureHandler flags across a partial config update

[m-bert]

Description

RNNativeViewGestureHandler updateConfig: read shouldActivateOnStart, disallowInterruption, yieldsToContinuousGestures and delaysChildPressedState without nil checks, unlike every other handler. A full config set carries all keys, so it was fine. A partial updateGestureHandlerConfig carries only the changed key. After the first such update the three flags were NO and delaysChildPressedState was back to YES, which was also re-applied to the wrapped scroll view. They stayed wrong until the next React render of the owner re-sent the full config.

Reproduced with a RawButton (disallowInterruption, shouldCancelWhenOutside bound to a SharedValue) inside a long-press detector: after each SharedValue change, the next press let the outer long press activate once, until the owner's re-render restored the flag.

Test plan

Tested on the following code:

import React, { useState } from 'react';
import { StyleSheet, Text, View } from 'react-native';
import {
  GestureDetector,
  Pressable,
  RawButton,
  useLongPressGesture,
} from 'react-native-gesture-handler';
import { useSharedValue } from 'react-native-reanimated';

// iOS. `RNNativeViewHandler updateConfig:` reads its four keys without nil
// checks, so any partial update (here: the `shouldCancelWhenOutside`
// SharedValue) resets `disallowInterruption` to NO. On iOS that flag only acts
// in the UIControl touch-down path, and the v3 detector reaches a UIControl
// only through RNGH's own button (Fabric TextInput/Switch wrappers hide theirs),
// so the target is `RawButton`, whose wrapper forwards `disallowInterruption`.
// With the flag set, touching the button cancels every other handler on the
// touch, so the outer long press never activates.
//
// Steps: hold a finger on the button for ~1s. Expected: long press stays at 0
// (cancelled by the native handler) and native begins goes up by 1. Press
// "Toggle SV" (sends the SharedValue false then true as partial updates), hold
// again. Bug: long press activates. Fixed: still 0.

const LONG_PRESS_MS = 400;

export default function EmptyExample() {
  const cancelWhenOutside = useSharedValue(false);
  const [toggles, setToggles] = useState(0);
  const [nativeBegins, setNativeBegins] = useState(0);
  const [longPresses, setLongPresses] = useState(0);

  const longPress = useLongPressGesture({
    runOnJS: true,
    minDuration: LONG_PRESS_MS,
    maxDistance: 50,
    onActivate: () => {
      setLongPresses((n) => n + 1);
    },
  });

  return (
    <View style={styles.container}>
      <Text style={styles.label} testID="status">
        SV toggles: {toggles}, native begins: {nativeBegins}, long presses:{' '}
        {longPresses}
      </Text>
      <Text style={styles.hint}>
        Hold on the button for ~1s. Each hold must add 1 to native begins
        (UIControl touch-down reached the handler). Before the toggle the long
        press must stay at 0. After the toggle it must still stay at 0 (bug: it
        counts).
      </Text>

      <Pressable
        style={styles.button}
        testID="toggle"
        onPress={() => {
          // Two partial updates; the flag ends where it started.
          cancelWhenOutside.value = true;
          cancelWhenOutside.value = false;
          setToggles((n) => n + 1);
        }}>
        <Text style={styles.buttonLabel}>Toggle SV</Text>
      </Pressable>

      <GestureDetector gesture={longPress}>
        <View style={styles.outer} testID="outer">
          <Text style={styles.outerLabel}>outer: long press</Text>
          <RawButton
            style={styles.input}
            testID="button"
            disallowInterruption
            shouldCancelWhenOutside={cancelWhenOutside}
            onBegin={() => {
              setNativeBegins((n) => n + 1);
            }}>
            <Text style={styles.inputLabel}>
              RawButton, disallowInterruption
            </Text>
          </RawButton>
        </View>
      </GestureDetector>
    </View>
  );
}

const styles = StyleSheet.create({
  container: {
    flex: 1,
    alignItems: 'center',
    padding: 16,
  },
  label: {
    fontSize: 14,
    color: '#001a72',
    marginVertical: 4,
    textAlign: 'center',
  },
  hint: {
    fontSize: 12,
    color: '#555',
    marginVertical: 4,
    textAlign: 'center',
  },
  button: {
    marginVertical: 12,
    paddingHorizontal: 20,
    paddingVertical: 10,
    borderRadius: 8,
    backgroundColor: '#782aeb',
  },
  buttonLabel: {
    color: 'white',
    fontSize: 16,
  },
  outer: {
    marginTop: 12,
    width: 300,
    padding: 24,
    borderRadius: 16,
    backgroundColor: '#f6b914',
    alignItems: 'center',
  },
  outerLabel: {
    color: 'white',
    fontSize: 16,
    marginBottom: 12,
  },
  input: {
    width: 240,
    height: 56,
    borderRadius: 8,
    backgroundColor: 'white',
    justifyContent: 'center',
    alignItems: 'center',
  },
  inputLabel: {
    color: '#001a72',
    fontSize: 14,
  },
});

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• packages/react-native-gesture-handler/apple/Handlers/RNNativeViewHandler.mm

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📝 Summary

Summary by CodeRabbit

• Bug Fixes
  • Gesture handler configuration updates now preserve existing settings when individual options are omitted.
  • Resetting configuration restores consistent default behavior, including child pressed-state delays.
  • Changes to child pressed-state delays are applied immediately to connected scroll views on supported platforms. This keeps scroll-view touch behavior in sync with the current gesture handler configuration.

The native view handler now resets configuration fields to defaults and preserves current values when configuration updates omit keys. On non-macOS platforms, changes to delaysChildPressedState update the connected scroll view when the recognizer is attached to a view.

Changes: Native view configuration

Layer / File(s)	Summary
Configuration reset and selective updates packages/react-native-gesture-handler/apple/Handlers/RNNativeViewHandler.mm	resetConfig restores default property values. updateConfig: changes properties only when their keys are present. A helper applies delaysChildPressedState to the connected scroll view when the recognizer is attached to a view on non-macOS platforms.

Priority: ➖ Normal

Merge Risk: ⚪ Minimal · up to ef104

The partial-update changes preserve omitted option values. Button-bound scroll-delay application remains limited as before, so no new merge-blocking behavior is established.

Pre-merge checks: 3

Passed checks: 3 passed

Check name	Status	Explanation
Title check		The title clearly and concisely describes the main change: preserving NativeViewGestureHandler flags during partial configuration updates on iOS.
Linked Issues check		Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check		Check skipped because no linked issues were found for this pull request.

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Pull request overview

This pull request fixes iOS native view gesture handler partial updates so unchanged flags and scroll-view delay settings are preserved.

Changes:

• Adds reset defaults.
• Applies only explicitly provided configuration values.
• Centralizes delay synchronization.

File summaries

File	Summary
packages/react-native-gesture-handler/apple/Handlers/RNNativeViewHandler.mm	Preserves handler flags across partial configuration updates.

Review details

• Files reviewed: 1/1 changed files
• Comments generated: 0
• Review effort level: Lite

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Inline comments:
In `@packages/react-native-gesture-handler/apple/Handlers/RNNativeViewHandler.mm`:
- Around line 145-146: Update applyDelaysChildPressedState to resolve the
enclosing scroll view from _boundView before applying delaysContentTouches,
rather than relying on recognizer.view or passing the UIControl directly.
Preserve the existing behavior for recognized scroll-view types and ensure
updateConfig-triggered delaysChildPressedState changes reach the enclosing
scroll view.

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• packages/react-native-gesture-handler/apple/Handlers/RNNativeViewHandler.mm

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