react-native-gesture-handler/lib/module/handlers/gestures/GestureDetector/useDetectorUpdater.js

Declarative API exposing native platform touch and gesture system to React Native

import { useCallback } from 'react';
import { attachHandlers } from './attachHandlers';
import { updateHandlers } from './updateHandlers';
import { needsToReattach } from './needsToReattach';
import { dropHandlers } from './dropHandlers';
import { useForceRender, validateDetectorChildren } from './utils';
import findNodeHandle from '../../../findNodeHandle'; // Returns a function that's responsible for updating the attached gestures
// If the view has changed, it will reattach the handlers to the new view
// If the view remains the same, it will update the handlers with the new config

export function useDetectorUpdater(state, preparedGesture, gesturesToAttach, gestureConfig, webEventHandlersRef) {
  const forceRender = useForceRender();
  const updateAttachedGestures = useCallback( // skipConfigUpdate is used to prevent unnecessary updates when only checking if the view has changed
  skipConfigUpdate => {
    // If the underlying view has changed we need to reattach handlers to the new view
    const viewTag = findNodeHandle(state.viewRef);
    const didUnderlyingViewChange = viewTag !== state.previousViewTag;

    if (didUnderlyingViewChange || needsToReattach(preparedGesture, gesturesToAttach)) {
      validateDetectorChildren(state.viewRef);
      dropHandlers(preparedGesture);
      attachHandlers({
        preparedGesture,
        gestureConfig,
        gesturesToAttach,
        webEventHandlersRef,
        viewTag
      });

      if (didUnderlyingViewChange) {
        state.previousViewTag = viewTag;
        state.forceRebuildReanimatedEvent = true;
        forceRender();
      }
    } else if (!skipConfigUpdate) {
      updateHandlers(preparedGesture, gestureConfig, gesturesToAttach);
    }
  }, [forceRender, gestureConfig, gesturesToAttach, preparedGesture, state, webEventHandlersRef]);
  return updateAttachedGestures;
}
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