使用 Reanimated 在 React Native 中构建具有自动滚动、无限循环、分页功能的可定制轮播

在 React Native 中创建自定义轮播是为应用程序添加视觉效果和交互性的好方法。在本博客中，我们将探索如何使用 React Native 的 Animated 和 Reanimated 库构建包含自动滚动功能的轮播。我们还将实现一个带有动画点和优雅的图像过渡效果的分页系统。

概述

在本教程中，我们将介绍以下内容：

• 设置自定义轮播组件。
• 使用 Reanimated 实现流畅的动画和插值。
• 自动滚动功能，可在图像之间自动旋转。
• 构建一个带有动画点指示器的分页系统。

我们将构建什么：

• 带有动画过渡的水平滚动轮播。
• 当用户与轮播交互时自动滚动暂停。
• 根据当前可见项目更新的分页点。

让我们开始吧！

---

1. 设置轮播组件

我们首先创建 CustomCarousel 组件，它将容纳轮播的核心逻辑。主要元素包括：

• 用于渲染项目的 Animated.FlatList。
• 使用 setInterval 的自动滚动机制。
• Reanimated的scrollTo和useSharedValue用于动画转换。

/* eslint-disable react-native/no-inline-styles */
import React, { useEffect, useRef, useState } from 'react';
import { StyleSheet, View, useWindowDimensions } from 'react-native';
import Animated, {
  scrollTo,
  useAnimatedRef,
  useAnimatedScrollHandler,
  useDerivedValue,
  useSharedValue,
} from 'react-native-reanimated';
import { hpx } from '../../helpers';
import Pagination from './Pagination';
import RenderItem from './RenderItem';
import { animals } from './constants';

const CustomCarousel = () => {
  const x = useSharedValue(0);
  const [data, setData] = useState(animals);
  const { width } = useWindowDimensions();
  const [currentIndex, setCurrentIndex] = useState(0);
  const [paginationIndex, setPaginationIndex] = useState(0);
  const ref = useAnimatedRef();
  const [isAutoPlay, setIsAutoPlay] = useState(true);
  const interval = useRef();
  const offset = useSharedValue(0);

  console.log('CURRENT_CAROUSEL_ITEM?', paginationIndex);

  const onViewableItemsChanged = ({ viewableItems }) => {
    if (viewableItems[0].index !== undefined && viewableItems[0].index !== null) {
      setCurrentIndex(viewableItems[0].index);
      setPaginationIndex(viewableItems[0].index % animals.length);
    }
  };

  const viewabilityConfig = {
    itemVisiblePercentThreshold: 50,
  };

  const viewabilityConfigCallbackPairs = useRef([{ viewabilityConfig, onViewableItemsChanged }]);

  const onScroll = useAnimatedScrollHandler({
    onScroll: (e) => {
      x.value = e.contentOffset.x;
    },
    onMomentumEnd: (e) => {
      offset.value = e.contentOffset.x;
    },
  });

  useDerivedValue(() => {
    scrollTo(ref, offset.value, 0, true);
  });

  useEffect(() => {
    if (isAutoPlay === true) {
      interval.current = setInterval(() => {
        offset.value += width;
      }, 4000);
    } else {
      clearInterval(interval.current);
    }
    return () => {
      clearInterval(interval.current);
    };
  }, [isAutoPlay, offset, width]);

  return (
    <view style="{styles.container}">
      <animated.flatlist ref="{ref}" style="{{" height: hpx flexgrow: onscrollbegindrag="{()"> {
          setIsAutoPlay(false);
        }}
        onScrollEndDrag={() => {
          setIsAutoPlay(true);
        }}
        onScroll={onScroll}
        scrollEventThrottle={16}
        horizontal
        bounces={false}
        pagingEnabled
        showsHorizontalScrollIndicator={false}
        viewabilityConfigCallbackPairs={viewabilityConfigCallbackPairs.current}
        onEndReached={() => setData([...data, ...animals])}
        onEndReachedThreshold={0.5}
        data={data}
        keyExtractor={(_, index) => `list_item${index}`}
        renderItem={({ item, index }) => {
          return <renderitem item="{item}" index="{index}" x="{x}"></renderitem>;
        }}
      />
      <pagination paginationindex="{paginationIndex}"></pagination>
    </animated.flatlist></view>
  );
};

export default CustomCarousel;

const styles = StyleSheet.create({
  container: {
    flex: 1,
  },
  buttonContainer: {
    justifyContent: 'center',
    alignItems: 'center',
    flexDirection: 'row',
    gap: 14,
  },
});

2. 分页组件

分页组件显示点来指示当前活动的幻灯片。每个点的不透明度都会根据轮播的当前索引而变化。

import React from 'react';
import { StyleSheet, View } from 'react-native';
import { hpx } from '../../helpers';
import Dot from './Dot';
import { animals } from './constants';

const Pagination = ({ paginationIndex }) => {
  return (
    <view style="{styles.container}">
      {animals.map((_, index) => {
        return <dot index="{index}" key="{index}" paginationindex="{paginationIndex}"></dot>;
      })}
    </view>
  );
};

export default Pagination;

const styles = StyleSheet.create({
  container: {
    flexDirection: 'row',
    marginTop: hpx(16),
    justifyContent: 'center',
    alignItems: 'center',
  },
});

3. 点组件

Dot 组件处理分页系统中每个点的外观。它根据点是否处于活动状态（当前索引）来更改其样式。

import React from 'react';
import { StyleSheet, View } from 'react-native';
import { Colors } from '../../assets';
import { hpx, wpx } from '../../helpers';

const Dot = ({ index, paginationIndex }) => {
  return <view style="{paginationIndex" index styles.dot : styles.dotopacity></view>;
};

export default Dot;

const styles = StyleSheet.create({
  dot: {
    backgroundColor: Colors.white,
    height: hpx(3),
    width: wpx(12),
    marginHorizontal: 2,
    borderRadius: 8,
  },
  dotOpacity: {
    backgroundColor: Colors.white,
    height: hpx(3),
    width: wpx(12),
    marginHorizontal: 2,
    borderRadius: 8,
    opacity: 0.5,
  },
});

4. RenderItem 组件

RenderItem 组件显示每个轮播项目。它利用 Reanimated 的插值函数来为项目滚动时的不透明度设置动画。

import React from 'react';
import { StyleSheet, useWindowDimensions, View } from 'react-native';
import Animated, { Extrapolation, interpolate, useAnimatedStyle } from 'react-native-reanimated';
import { hpx, nf, SCREEN_WIDTH, wpx } from '../../helpers/Scale';

const RenderItem = ({ item, index, x }) => {
  const { width } = useWindowDimensions();

  const animatedStyle = useAnimatedStyle(() => {
    const opacityAnim = interpolate(
      x.value,
      [(index - 1) * width, index * width, (index + 1) * width],
      [-0.3, 1, -0.3],
      Extrapolation.CLAMP
    );
    return {
      opacity: opacityAnim,
    };
  });

  return (
    <view style="{{" width>
      <animated.image resizemode="cover" source="{{" uri: item.image style="{[styles.titleImage," animatedstyle></animated.image>
    </view>
  );
};

export default RenderItem;

const styles = StyleSheet.create({
  titleImage: {
    width: SCREEN_WIDTH - wpx(32), // adjust the width of the image and horizontal padding
    height: hpx(194),
    alignSelf: 'center',
    borderRadius: nf(16),
  },
});

5. 自动滚动

自动滚动功能是通过setInterval实现的。此方法可确保轮播每 4 秒自动从一张幻灯片移动到下一张幻灯片。如果用户通过拖动与轮播交互，自动滚动就会暂停。

6. 常量文件

/* eslint-disable react-native/no-inline-styles */
import React, { useEffect, useRef, useState } from 'react';
import { StyleSheet, View, useWindowDimensions } from 'react-native';
import Animated, {
  scrollTo,
  useAnimatedRef,
  useAnimatedScrollHandler,
  useDerivedValue,
  useSharedValue,
} from 'react-native-reanimated';
import { hpx } from '../../helpers';
import Pagination from './Pagination';
import RenderItem from './RenderItem';
import { animals } from './constants';

const CustomCarousel = () => {
  const x = useSharedValue(0);
  const [data, setData] = useState(animals);
  const { width } = useWindowDimensions();
  const [currentIndex, setCurrentIndex] = useState(0);
  const [paginationIndex, setPaginationIndex] = useState(0);
  const ref = useAnimatedRef();
  const [isAutoPlay, setIsAutoPlay] = useState(true);
  const interval = useRef();
  const offset = useSharedValue(0);

  console.log('CURRENT_CAROUSEL_ITEM?', paginationIndex);

  const onViewableItemsChanged = ({ viewableItems }) => {
    if (viewableItems[0].index !== undefined && viewableItems[0].index !== null) {
      setCurrentIndex(viewableItems[0].index);
      setPaginationIndex(viewableItems[0].index % animals.length);
    }
  };

  const viewabilityConfig = {
    itemVisiblePercentThreshold: 50,
  };

  const viewabilityConfigCallbackPairs = useRef([{ viewabilityConfig, onViewableItemsChanged }]);

  const onScroll = useAnimatedScrollHandler({
    onScroll: (e) => {
      x.value = e.contentOffset.x;
    },
    onMomentumEnd: (e) => {
      offset.value = e.contentOffset.x;
    },
  });

  useDerivedValue(() => {
    scrollTo(ref, offset.value, 0, true);
  });

  useEffect(() => {
    if (isAutoPlay === true) {
      interval.current = setInterval(() => {
        offset.value += width;
      }, 4000);
    } else {
      clearInterval(interval.current);
    }
    return () => {
      clearInterval(interval.current);
    };
  }, [isAutoPlay, offset, width]);

  return (
    <view style="{styles.container}">
      <animated.flatlist ref="{ref}" style="{{" height: hpx flexgrow: onscrollbegindrag="{()"> {
          setIsAutoPlay(false);
        }}
        onScrollEndDrag={() => {
          setIsAutoPlay(true);
        }}
        onScroll={onScroll}
        scrollEventThrottle={16}
        horizontal
        bounces={false}
        pagingEnabled
        showsHorizontalScrollIndicator={false}
        viewabilityConfigCallbackPairs={viewabilityConfigCallbackPairs.current}
        onEndReached={() => setData([...data, ...animals])}
        onEndReachedThreshold={0.5}
        data={data}
        keyExtractor={(_, index) => `list_item${index}`}
        renderItem={({ item, index }) => {
          return <renderitem item="{item}" index="{index}" x="{x}"></renderitem>;
        }}
      />
      <pagination paginationindex="{paginationIndex}"></pagination>
    </animated.flatlist></view>
  );
};

export default CustomCarousel;

const styles = StyleSheet.create({
  container: {
    flex: 1,
  },
  buttonContainer: {
    justifyContent: 'center',
    alignItems: 'center',
    flexDirection: 'row',
    gap: 14,
  },
});

7. 结论

在本教程中，我们使用 React Native 的 FlatList 以及 Reanimated 构建了一个自定义轮播以实现流畅的动画和插值。我们添加了带有动画点、自动滚动功能的分页系统，并确保用户交互会暂停和恢复自动滚动功能。

使用这些组件，您可以扩展轮播以包含其他功能，例如动态内容、可点击项目和更复杂的动画。 React Native 与 Reanimated 的灵活性允许以最低的性能成本实现高度可定制的轮播，这对于创建具有视觉吸引力的移动应用程序非常有用。

请随意在您的项目中尝试这一点，并自定义样式和行为以满足您的设计需求！

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