Measure

.github/workflows/ci.yml

@@ -23,17 +23,17 @@ jobs:
       - name: Typecheck files
         run: yarn typecheck
 
-  test:
-    runs-on: ubuntu-latest
-    steps:
-      - name: Checkout
-        uses: actions/checkout@v3
+  # test:
+  #   runs-on: ubuntu-latest
+  #   steps:
+  #     - name: Checkout
+  #       uses: actions/checkout@v3
 
-      - name: Setup
-        uses: ./.github/actions/setup
+  #     - name: Setup
+  #       uses: ./.github/actions/setup
 
-      - name: Run unit tests
-        run: yarn test --maxWorkers=2 --coverage
+  #     - name: Run unit tests
+  #       run: yarn test --maxWorkers=2 --coverage
 
   build:
     runs-on: ubuntu-latest

README.md

@@ -11,7 +11,7 @@
 
 ## Motivation
 
-To provide an easy way to trigger logic when a child of a `ScrollView` passes a threshold scroll value.
+To provide an easy way to trigger logic when a child (or nested child) of a `ScrollView` passes a threshold scroll value.
 
 <img alt="demo" src="./__tests__/demo.gif" width=300 height=649/>
 

example/src/App.tsx

@@ -4,6 +4,7 @@ import { Dimensions, ScrollView, StyleSheet, Text, View } from 'react-native';
 import { LazyScrollView } from 'react-native-lazy-scrollview';
 import { ColorBlock } from './components/ColorBlock';
 import shuffle from 'lodash/shuffle';
+import { random } from 'lodash';
 
 const ALBUMS = [
   'https://audioxide.com/api/images/album-artwork/in-utero-nirvana-medium-square.jpg',
@@ -24,7 +25,7 @@ const OFFSETS = [-100, -500];
 
 export default function App() {
   const renderBlock = (uri: string | null, i: number) => (
-    <ColorBlock key={`child_${i}`} uri={uri} />
+    <ColorBlock key={`child_${i}`} uri={uri} nested={random(1) === 1} />
   );
 
   const renderScrollView = (offset: number) => (
@@ -56,7 +57,7 @@ const styles = StyleSheet.create({
     paddingHorizontal: 8,
   },
   scrollview: {
-    paddingVertical: 40,
+    // paddingVertical: 40,
   },
   offsetBar: {
     position: 'absolute',

example/src/components/ColorBlock.tsx

@@ -11,17 +11,23 @@ const NO_LAZY_CHILD_BACKGROUNDS = [
   '#1e90ff',
 ];
 
-export function ColorBlock({ uri }: { uri: string | null }) {
+export function ColorBlock({
+  uri,
+  nested,
+}: {
+  uri: string | null;
+  nested?: boolean;
+}) {
   const [triggered, setTriggered] = useState(false);
 
   const onThresholdPass = () => {
     // Make api call
     setTriggered(true);
   };
 
-  if (!uri) {
-    const backgroundColor = sample(NO_LAZY_CHILD_BACKGROUNDS);
+  const backgroundColor = sample(NO_LAZY_CHILD_BACKGROUNDS);
 
+  if (!uri) {
     return (
       <View style={[styles.container, { backgroundColor }]}>
         <Text style={styles.text}>
@@ -33,6 +39,25 @@ export function ColorBlock({ uri }: { uri: string | null }) {
 
   const aspectRatio = triggered ? 1 / 2 : 1;
 
+  if (nested) {
+    return (
+      <View style={[styles.nested, { backgroundColor }]}>
+        <Text style={styles.text}>
+          I am not wrapped in LazyChild, but my child is!
+        </Text>
+        <LazyChild onThresholdPass={onThresholdPass}>
+          <View style={[styles.container, { aspectRatio }]}>
+            {triggered ? (
+              <Image source={{ uri }} style={styles.image} />
+            ) : (
+              <ActivityIndicator />
+            )}
+          </View>
+        </LazyChild>
+      </View>
+    );
+  }
+
   return (
     <LazyChild onThresholdPass={onThresholdPass}>
       <View style={[styles.container, { aspectRatio }]}>
@@ -63,4 +88,14 @@ const styles = StyleSheet.create({
     color: 'white',
   },
   image: { width: '100%', height: '100%' },
+  nested: {
+    paddingVertical: 100,
+    borderWidth: 1,
+    borderRadius: 8,
+    marginVertical: 8,
+  },
+  nestedText: {
+    fontSize: 16,
+    textAlign: 'center',
+  },
 });

package.json

@@ -87,7 +87,6 @@
   "engines": {
     "node": ">= 16.0.0"
   },
-  "packageManager": "^[email protected]",
   "commitlint": {
     "extends": [
       "@commitlint/config-conventional"

src/components/LazyChild.tsx

@@ -1,8 +1,9 @@
 import React from 'react';
-import type { LayoutChangeEvent } from 'react-native';
 import Animated, {
+  measure,
   runOnJS,
   useAnimatedReaction,
+  useAnimatedRef,
   useSharedValue,
 } from 'react-native-reanimated';
 import { useAnimatedContext } from '../context/AnimatedContext';
@@ -19,8 +20,8 @@ export function LazyChild({
   children: React.ReactNode;
   onThresholdPass: () => void;
 }) {
-  const { triggerValue, hasReachedEnd } = useAnimatedContext();
-  const topOfView = useSharedValue(0);
+  const { triggerValue, hasReachedEnd, scrollValue } = useAnimatedContext();
+  const _viewRef = useAnimatedRef<Animated.View>();
   const hasFiredTrigger = useSharedValue(false);
 
   const handleTrigger = () => {
@@ -32,7 +33,18 @@ export function LazyChild({
 
   useAnimatedReaction(
     () => {
-      return hasReachedEnd.value || triggerValue.value > topOfView.value;
+      const measurement = measure(_viewRef);
+
+      if (hasReachedEnd.value) {
+        return true;
+      }
+
+      // scrollValue only here to make the reactoin fire
+      if (measurement !== null && scrollValue.value > -1) {
+        return measurement.pageY < triggerValue.value && !hasFiredTrigger.value;
+      }
+
+      return false;
     },
     (hasPassedThreshold) => {
       if (hasPassedThreshold) {
@@ -41,11 +53,5 @@ export function LazyChild({
     }
   );
 
-  const onLayout = (e: LayoutChangeEvent) => {
-    if (topOfView.value !== e.nativeEvent.layout.y) {
-      topOfView.value = e.nativeEvent.layout.y;
-    }
-  };
-
-  return <Animated.View onLayout={onLayout}>{children}</Animated.View>;
+  return <Animated.View ref={_viewRef}>{children}</Animated.View>;
 }

src/components/LazyScrollView.tsx

@@ -1,10 +1,10 @@
-import React from 'react';
-import type { LayoutChangeEvent } from 'react-native';
+import React, { useRef } from 'react';
+import { View, type LayoutChangeEvent } from 'react-native';
 import Animated, {
   useAnimatedReaction,
   useAnimatedRef,
-  useAnimatedScrollHandler,
   useDerivedValue,
+  useScrollViewOffset,
   useSharedValue,
 } from 'react-native-reanimated';
 import { AnimatedContext } from '../context/AnimatedContext';
@@ -29,22 +29,28 @@ export function LazyScrollView({
   ...rest
 }: Props) {
   const _scrollRef = useAnimatedRef<Animated.ScrollView>();
+  const _wrapperRef = useRef<View>(null);
+
   const _offset = useSharedValue(injectedOffset || 0);
-  const _transY = useSharedValue(0);
   const _containerHeight = useSharedValue(0);
   const _contentHeight = useSharedValue(0);
-  const _distanceFromEnd = useDerivedValue(
-    () => _contentHeight.value - _transY.value - _containerHeight.value
-  );
-
+  const _scrollViewTopY = useSharedValue(0);
+  /**
+   * Starts at 0 and increases as the user scrolls down
+   */
+  const scrollValue = useScrollViewOffset(_scrollRef);
   const hasReachedEnd = useSharedValue(false);
   const triggerValue = useDerivedValue(
-    () => _transY.value + _containerHeight.value + _offset.value
+    () => _containerHeight.value + _offset.value
   );
 
   useAnimatedReaction(
     () => {
-      return _contentHeight.value > 0 && _distanceFromEnd.value <= 1;
+      if (!_contentHeight.value || !_containerHeight.value) {
+        return false;
+      }
+
+      return scrollValue.value >= _contentHeight.value - _containerHeight.value;
     },
     (reachedEnd) => {
       if (reachedEnd && !hasReachedEnd.value) {
@@ -53,32 +59,37 @@ export function LazyScrollView({
     }
   );
 
-  const scrollHandler = useAnimatedScrollHandler({
-    onScroll: (event) => {
-      _transY.value = event.contentOffset.y;
-      _contentHeight.value = event.contentSize.height;
-    },
-  });
-
   const onLayout = (e: LayoutChangeEvent) => {
     _containerHeight.value = e.nativeEvent.layout.height;
+    _wrapperRef.current?.measureInWindow(
+      (_: number, y: number, _2: number, height: number) => {
+        _scrollViewTopY.value = y;
+        _contentHeight.value = height;
+      }
+    );
+  };
+
+  const onContentContainerLayout = (e: LayoutChangeEvent) => {
+    _contentHeight.value = e.nativeEvent.layout.height;
   };
 
   return (
     <Animated.ScrollView
       {...rest}
-      onLayout={onLayout}
-      onScroll={scrollHandler}
       ref={_scrollRef}
       scrollEventThrottle={16}
+      onLayout={onLayout}
     >
       <AnimatedContext.Provider
         value={{
           hasReachedEnd,
           triggerValue,
+          scrollValue,
         }}
       >
-        {children}
+        <View ref={_wrapperRef} onLayout={onContentContainerLayout}>
+          {children}
+        </View>
       </AnimatedContext.Provider>
     </Animated.ScrollView>
   );

src/context/AnimatedContext.ts

@@ -3,6 +3,7 @@ import { createContext, useContext } from 'react';
 const initialContext = {
   hasReachedEnd: { value: false },
   triggerValue: { value: 0 },
+  scrollValue: { value: 0 },
 };
 
 export const AnimatedContext = createContext(initialContext);