react-native-reanimated/lib/module/reanimated2/hook/useScrollViewOffset.js

More powerful alternative to Animated library for React Native.

'use strict';

import { useEffect, useRef, useCallback } from 'react';
import { useEvent } from './useEvent';
import { useSharedValue } from './useSharedValue';
import { isWeb } from '../PlatformChecker';
const IS_WEB = isWeb();

/**
 * Lets you synchronously get the current offset of a `ScrollView`.
 *
 * @param animatedRef - An [animated ref](https://docs.swmansion.com/react-native-reanimated/docs/core/useAnimatedRef) attached to an Animated.ScrollView component.
 * @returns A shared value which holds the current offset of the `ScrollView`.
 * @see https://docs.swmansion.com/react-native-reanimated/docs/scroll/useScrollViewOffset
 */
export const useScrollViewOffset = IS_WEB ? useScrollViewOffsetWeb : useScrollViewOffsetNative;
function useScrollViewOffsetWeb(animatedRef, providedOffset) {
  const internalOffset = useSharedValue(0);
  const offset = useRef(providedOffset ?? internalOffset).current;
  const scrollRef = useRef(null);
  const eventHandler = useCallback(() => {
    'worklet';

    const element = getWebScrollableElement(animatedRef.current);
    // scrollLeft is the X axis scrolled offset, works properly also with RTL layout
    offset.value = element.scrollLeft === 0 ? element.scrollTop : element.scrollLeft;
    // eslint-disable-next-line react-hooks/exhaustive-deps
  }, [animatedRef, animatedRef.current]);
  useEffect(() => {
    // We need to make sure that listener for old animatedRef value is removed
    if (scrollRef.current !== null) {
      getWebScrollableElement(scrollRef.current).removeEventListener('scroll', eventHandler);
    }
    scrollRef.current = animatedRef.current;
    const element = getWebScrollableElement(animatedRef.current);
    element.addEventListener('scroll', eventHandler);
    return () => {
      element.removeEventListener('scroll', eventHandler);
    };
    // React here has a problem with `animatedRef.current` since a Ref .current
    // field shouldn't be used as a dependency. However, in this case we have
    // to do it this way.
    // eslint-disable-next-line react-hooks/exhaustive-deps
  }, [animatedRef, animatedRef.current, eventHandler]);
  return offset;
}
function useScrollViewOffsetNative(animatedRef, providedOffset) {
  const internalOffset = useSharedValue(0);
  const offset = useRef(providedOffset ?? internalOffset).current;
  const scrollRef = useRef(null);
  const scrollRefTag = useRef(null);
  const eventHandler = useEvent(event => {
    'worklet';

    offset.value = event.contentOffset.x === 0 ? event.contentOffset.y : event.contentOffset.x;
  }, scrollNativeEventNames
  // Read https://github.com/software-mansion/react-native-reanimated/pull/5056
  // for more information about this cast.
  );
  useEffect(() => {
    // We need to make sure that listener for old animatedRef value is removed
    if (scrollRef.current !== null && scrollRefTag.current !== null) {
      eventHandler.workletEventHandler.unregisterFromEvents(scrollRefTag.current);
    }

    // Store the ref and viewTag for future cleanup
    scrollRef.current = animatedRef.current;
    scrollRefTag.current = animatedRef.getTag();
    if (scrollRefTag === null) {
      console.warn('[Reanimated] ScrollViewOffset failed to resolve the view tag from animated ref. Did you forget to attach the ref to a component?');
    } else {
      eventHandler.workletEventHandler.registerForEvents(scrollRefTag.current);
    }
    return () => {
      if (scrollRefTag.current !== null) {
        eventHandler.workletEventHandler.unregisterFromEvents(scrollRefTag.current);
      }
    };
    // React here has a problem with `animatedRef.current` since a Ref .current
    // field shouldn't be used as a dependency. However, in this case we have
    // to do it this way.
    // eslint-disable-next-line react-hooks/exhaustive-deps
  }, [animatedRef, animatedRef.current, eventHandler]);
  return offset;
}
function getWebScrollableElement(scrollComponent) {
  return (scrollComponent === null || scrollComponent === void 0 ? void 0 : scrollComponent.getScrollableNode()) ?? scrollComponent;
}
const scrollNativeEventNames = ['onScroll', 'onScrollBeginDrag', 'onScrollEndDrag', 'onMomentumScrollBegin', 'onMomentumScrollEnd'];
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