React useCallback使用

轮播图组建需要自动轮播，我想到了使用 setTimeout 来解决 setInterval 可能越来越快的问题。心里想着：这我还不轻松拿下？一番奋战后于是就有了以下代码

tsx

const Swiper: React.FC<SwiperProps> = (props) => {
    const {
        autoplay,
        duration,
    } = props;

    const [currentIndex, setCurrentIndex] = useState<number>(0);
    const [timer, setTimer] = useState<number>();
    const childrenLength = React.Children.count(children);

    function next() {
        if (currentIndex > childrenLength - 2) {
            setCurrentIndex(0);
        }
        else {
            setCurrentIndex(currentIndex + 1);
        }
    }

    function prev() {
        if (currentIndex <= 0) {
            setCurrentIndex(childrenLength - 1);
        }
        else {
            setCurrentIndex(currentIndex - 1);
        }
    }

    // TODO autoplay
    function autoPlay() {
        if (autoplay) {
            // eslint-disable-next-line unicorn/no-new-array
            new Array(React.Children.count(children))
                .fill(0)
                .forEach(() => {
                    return new Promise((resolve) => {
                        const timerId = setTimeout(() => {
                            next();
                        }, duration);
                        setTimer(timerId);
                        resolve(true);
                    });
                });
        }
    }

    useEffect(() => {
        autoPlay(); // error
        return () => {
            if (autoplay)
                clearTimeout(timer);
        };
    }, [timer, currentIndex, autoplay]);

    return (
    // ...组件内容
        <div />
    );
};

Swiper.defaultProps = {
    // ...
};

export default Swiper;

提醒

Warning: Maximum update depth exceeded. This can happen when a component calls setState inside useEffect, but useEffect either doesn't have a dependency array, or one of the dependencies changes on every render

这时会报错且页面不能加载（报错详情见上文）。在我询问了群里的大佬后，得知有一个 useCallback 貌似可以解决我的问题。

于是按着大佬的思路，我做了如下改造:

使用 useCallback 将 next 和 autoPlay 进行了一次包装。

为什么要使用 useCallback 将 next 函数也进行改造呢？

不使用 useCallback 将 next 进行包裹会有如下报错： Warning: Maximum update depth exceeded. This can happen when a component calls setState inside useEffect, but useEffect either doesn't have a dependency array, or one of the dependencies changes on every render

tsx

const next = useCallback(() => {
    if (currentIndex > childrenLength - 2) {
        setCurrentIndex(0);
    }
    else {
        setCurrentIndex(currentIndex + 1);
    }
}, [currentIndex, childrenLength]);

useEffect(() => {
    // autoPlay();  // error
    const autoPlay = useCallback(() => {
        const timer = setTimeout(() => {
            next();
            autoPlay();
        }, duration);

        return () => {
            if (autoplay)
                clearTimeout(timer);
        };
    }, [timer, currentIndex, autoplay]);
}, [duration, next, autoplay]);

useEffect(() => {
    if (autoplay) {
        autoPlay();
    }
}, [autoplay, autoPlay]);

嘿嘿，有问题不能自己死磕，还是得问问！