React Native中上下滑动动画

Question

我在React Native中使用上下动画，但是动画只是从上到下滑动，然后停在底部我想连续上下移动它。我也使用了动画循环，所以请检查并为我提供解决方案

import React, { useEffect, useState } from 'react'
import { Text, View, Animated, Easing, StyleSheet } from 'react-native'
import LoaderLogo from '../../icons/commonicons/LoaderLogo'
import { Loadericon } from '../../constants/Image';
import LinearGradient from 'react-native-linear-gradient';
import { dynamicSize } from '../sizechoose';

const amimationScreen = () => {
    const startValue = new Animated.Value(0);
    const endValue = dynamicSize(225);

    const startValue2 = new Animated.Value(225);
    const endValue2 = dynamicSize(0);
    const duration = 5000;

    useEffect(() => {

        Animated.sequence([
            Animated.timing(startValue, {
                toValue: endValue,
                duration: duration,
                useNativeDriver: true,
            }),
            Animated.timing(startValue2, {
                toValue: endValue2,
                duration: duration,
                useNativeDriver: true,
            })
        ]).start()

    }, [startValue, endValue, duration]);

    return (
        <Animated.View style={[{ transform: [{ translateY: startValue }] }]}>
       <View style={{backgroundColor:'red',height:10,width:100}}>
            </View>
        </Animated.View>
    )
}


export default amimationScreen

我也尝试过使用react-native-animable包，但它对我来说不太好用，因为它从屏幕顶部开始动画。

Answer 1

这对我有用：

const App = () => {
  const animated = new Animated.Value(0);
  const duration = 5000;

  useEffect(() => {
    Animated.loop(
      Animated.sequence([
        Animated.timing(animated, {
          toValue: 255,
          duration: duration,
          useNativeDriver: true,
        }),
        Animated.timing(animated, {
          toValue: 0,
          duration: duration,
          useNativeDriver: true,
        }),
      ]),
    ).start();
  }, []);

  return (
    <Animated.View style={[{transform: [{translateY: animated}]}]}>
      <View style={{backgroundColor: 'red', height: 10, width: 100}}></View>
    </Animated.View>
  );
};

因此，不要使用两个

Animated.Value

实例进行翻译，而是创建一个实例并让它依次从

0

转换到

255

，然后从

255

转换回

0

。并在序列完成后使其循环。

---

我认为您原始方法中的主要问题是

startValue

决定视图如何转换，因为这是您作为

translateY

的值传递的内容。因此，在您的示例中，向下的动画会正确发生。但是，向上动画不会发生，因为

startValue2

被传递给

Animated.timing

并且

startValue

未用于翻译示例中的任何视图。

Answer 2

    import React, { useEffect, useRef, useState } from 'react';
    import { Animated, Dimensions, Easing, StyleSheet, View } from 'react-native';


    export const App = () => {
        const animatedValue = useRef(new Animated.Value(0)).current;
        const [isTop, setIsTop] = useState(true);

        const startAnimation = toValue => {
            Animated.timing(animatedValue, {
                toValue,
                duration: 1000,
                easing: Easing.linear,
                useNativeDriver: true
            }).start(() => {
                setIsTop(!isTop);
            })
        }

        useEffect(() => {
            startAnimation(isTop ? 1 : 0);
        }, [isTop]);

        const translateY = animatedValue.interpolate({
            inputRange: [0, 1],
            outputRange: [0, Dimensions.get('window').height - 70],
            extrapolate: 'clamp'
        })

        return (
            <View style={styles.container}>
                <Animated.View style={[styles.square, { transform: [{ translateY }] }]}>

                </Animated.View>
            </View>
        )
    }


    const styles = StyleSheet.create({
        container: {
            flex: 1,
            alignItems: 'center'
        },
        square: {
            width: 70,
            height: 70,
            backgroundColor: 'red'
        }
    });