使用reanimated，redash的react原生动画onScroll的问题

Question

你好，我正在尝试在React Native中实现动画。当我从scrollview向上滚动时，我想要scrollview中的一个子项是buttonContainer淡出。因此，当我开始向上滚动时，buttonContainer的不透明度可能从1变为0。但是，什么都没有发生。我不完全理解如何设置输入范围和输出范围。

Here is code in Snack

这里也有

import * as React from 'react';
import { Text, View, StyleSheet, Dimensions, Button } from 'react-native';
import Animated from 'react-native-reanimated';
import { onScroll } from 'react-native-redash';

const { height } = Dimensions.get('window');
const BUTTON_CONTAINER_HEIGHT = height / 1.7;
const { Value, interpolate, Extrapolate } = Animated;

export default class App extends React.Component {
  render() {
    const scrollY = new Value(0);
    const opacity = interpolate(scrollY, {
      inputRange: [BUTTON_CONTAINER_HEIGHT, height - 30],
      outputRange: [1, 0],
      extrapolate: Extrapolate.CLAMP,
    });
    return (
      <View style={{ flex: 1 }}>
        <View style={styles.container}>
          <Animated.ScrollView
            onScroll={onScroll({ scrollY })}
            showVerticalScrollIndicator={false}
            scrollEventThrottle={1}>
            <Animated.View
              style={[styles.buttonContainer, { opacity: opacity }]}>
              <Text>Hello World! </Text>
              <Button title="Click Me!" />
            </Animated.View>
            <View>
              <Text style={styles.textStyle}>This is content</Text>
              <Text style={styles.textStyle}>This is content</Text>
              <Text style={styles.textStyle}>This is content</Text>
              <Text style={styles.textStyle}>This is content</Text>
              <Text style={styles.textStyle}>This is content</Text>
              <Text style={styles.textStyle}>This is content</Text>
              <Text style={styles.textStyle}>This is content</Text>
              <Text style={styles.textStyle}>This is content</Text>
            </View>
          </Animated.ScrollView>
        </View>
      </View>
    );
  }
}

const styles = StyleSheet.create({
  container: {
    flex: 1,
    flexDirection: 'column',
    position: 'relative',
  },
  buttonContainer: {
    flex: 1,
    flexDirection: 'column',
    justifyContent: 'flex-end',
    alignItems: 'center',
    height: BUTTON_CONTAINER_HEIGHT,
    marginBottom: 30,
  },
  textStyle: {
    height: 100,
    fontSize: 24,
    marginTop: 10,
  },
});

Answer 1

您正在以错误的方式定义动画值，不要在render方法中定义值，因为它们将在每次组件重新呈现时创建，请使用以下代码在构造函数、中定义它们

import * as React from 'react';
import {Text, View, StyleSheet, Dimensions, Button} from 'react-native';
import {onScroll} from 'react-native-redash';
import Animated from 'react-native-reanimated';

const {height} = Dimensions.get('window');
const BUTTON_CONTAINER_HEIGHT = height / 1.7;
const {Value, interpolate, Extrapolate} = Animated;

export default class App extends React.Component<{}> {
  constructor(props: Readonly<{}>) {
    super(props);
    this.scrollY = new Value(0);
  }
  render() {
    const {scrollY} = this;
    const opacity = interpolate(scrollY, {
      inputRange: [0, BUTTON_CONTAINER_HEIGHT, height - 30],
      outputRange: [1, 0, 0],
      extrapolate: Extrapolate.CLAMP,
    });
    return (
      <View style={{flex: 1}}>
        <View style={styles.container}>
          <Animated.ScrollView
            onScroll={onScroll({y: scrollY})}
            showsVerticalScrollIndicator={false}
            scrollEventThrottle={1}>
            <Animated.View style={[styles.buttonContainer, {opacity}]}>
              <Text>Hello World! </Text>
              <Button onPress={() => {}} title="Click Me!" />
            </Animated.View>
            <View>
              <Text style={styles.textStyle}>This is content</Text>
              <Text style={styles.textStyle}>This is content</Text>
              <Text style={styles.textStyle}>This is content</Text>
              <Text style={styles.textStyle}>This is content</Text>
              <Text style={styles.textStyle}>This is content</Text>
              <Text style={styles.textStyle}>This is content</Text>
              <Text style={styles.textStyle}>This is content</Text>
              <Text style={styles.textStyle}>This is content</Text>
            </View>
          </Animated.ScrollView>
        </View>
      </View>
    );
  }
}

const styles = StyleSheet.create({
  container: {
    flex: 1,
    flexDirection: 'column',
    position: 'relative',
  },
  buttonContainer: {
    flex: 1,
    flexDirection: 'column',
    justifyContent: 'flex-end',
    alignItems: 'center',
    height: BUTTON_CONTAINER_HEIGHT,
    marginBottom: 30,
  },
  textStyle: {
    height: 100,
    fontSize: 24,
    marginTop: 10,
  },
});