使用 react-hooks 更新状态时执行异步代码 [英] Executing async code on update of state with react-hooks

问题描述

我有类似的东西:

const [loading, setLoading] = useState(false);

...

setLoading(true);
doSomething(); // <--- when here, loading is still false. 

设置状态仍然是异步的，那么等待这个 setLoading() 调用完成的最佳方法是什么?

Setting state is still async, so what's the best way to wait for this setLoading() call to be finished?

setLoading() 似乎不像过去的 setState() 那样接受回调.

The setLoading() doesn't seem to accept a callback like setState() used to.

getNextPage = () => {
    // This will scroll back to the top, and also trigger the prefetch for the next page on the way up.
    goToTop();

    if (this.state.pagesSeen.includes(this.state.page + 1)) {
      return this.setState({
        page: this.state.page + 1,
      });
    }

    if (this.state.prefetchedOrders) {
      const allOrders = this.state.orders.concat(this.state.prefetchedOrders);
      return this.setState({
        orders: allOrders,
        page: this.state.page + 1,
        pagesSeen: [...this.state.pagesSeen, this.state.page + 1],
        prefetchedOrders: null,
      });
    }

    this.setState(
      {
        isLoading: true,
      },
      () => {
        getOrders({
          page: this.state.page + 1,
          query: this.state.query,
          held: this.state.holdMode,
          statuses: filterMap[this.state.filterBy],
        })
          .then((o) => {
            const { orders } = o.data;
            const allOrders = this.state.orders.concat(orders);
            this.setState({
              orders: allOrders,
              isLoading: false,
              page: this.state.page + 1,
              pagesSeen: [...this.state.pagesSeen, this.state.page + 1],
              // Just in case we're in the middle of a prefetch.
              prefetchedOrders: null,
            });
          })
          .catch(e => console.error(e.message));
      },
    );
  };

转换为基于函数的

  const getNextPage = () => {
    // This will scroll back to the top, and also trigger the prefetch for the next page on the way up.
    goToTop();

    if (pagesSeen.includes(page + 1)) {
      return setPage(page + 1);
    }

    if (prefetchedOrders) {
      const allOrders = orders.concat(prefetchedOrders);
      setOrders(allOrders);
      setPage(page + 1);
      setPagesSeen([...pagesSeen, page + 1]);
      setPrefetchedOrders(null);
      return;
    }

    setIsLoading(true);

    getOrders({
      page: page + 1,
      query: localQuery,
      held: localHoldMode,
      statuses: filterMap[filterBy],
    })
      .then((o) => {
        const { orders: fetchedOrders } = o.data;
        const allOrders = orders.concat(fetchedOrders);

        setOrders(allOrders);
        setPage(page + 1);
        setPagesSeen([...pagesSeen, page + 1]);
        setPrefetchedOrders(null);
        setIsLoading(false);
      })
      .catch(e => console.error(e.message));
  };

在上面，我们希望按顺序运行每个 setWhatever 调用.这是否意味着我们需要设置许多不同的 useEffect 钩子来复制这种行为?

In the above, we want to run each setWhatever call sequentially. Does this mean we need to set up many different useEffect hooks to replicate this behavior?

推荐答案

useState setter 不会像 React 类组件中的 setState 那样在状态更新完成后提供回调.为了复制相同的行为，您可以在 React 类组件中使用类似于 componentDidUpdate 生命周期方法的类似模式和 useEffect using Hooks

useState setter doesn't provide a callback after state update is done like setState does in React class components. In order to replicate the same behaviour, you can make use of the a similar pattern like componentDidUpdate lifecycle method in React class components with useEffect using Hooks

useEffect hooks 将第二个参数作为一组值，React 需要在渲染周期完成后监视这些值的变化.

useEffect hooks takes the second parameter as an array of values which React needs to monitor for change after the render cycle is complete.

const [loading, setLoading] = useState(false);

...

useEffect(() => {
    doSomething(); // This is be executed when `loading` state changes
}, [loading])
setLoading(true);

编辑

与 setState 不同，useState 钩子的更新程序没有回调，但您始终可以使用 useEffect 来复制上述内容行为.但是你需要确定加载变化

Unlike setState, the updater for useState hook doesn't have a callback, but you can always use a useEffect to replicate the above behaviour. However you need to determine the loading change

代码的函数式方法看起来像

The functional approach to your code would look like

function usePrevious(value) {
  const ref = useRef();
  useEffect(() => {
    ref.current = value;
  });
  return ref.current;
}

<小时>

const prevLoading = usePrevious(isLoading);

useEffect(() => {
   if (!prevLoading && isLoading) {
       getOrders({
          page: page + 1,
          query: localQuery,
          held: localHoldMode,
          statuses: filterMap[filterBy],
      })
      .then((o) => {
        const { orders: fetchedOrders } = o.data;
        const allOrders = orders.concat(fetchedOrders);

        setOrders(allOrders);
        setPage(page + 1);
        setPagesSeen([...pagesSeen, page + 1]);
        setPrefetchedOrders(null);
        setIsLoading(false);
      })
      .catch(e => console.error(e.message));
   }
}, [isLoading, preFetchedOrders, orders, page, pagesSeen]);

const getNextPage = () => {
    // This will scroll back to the top, and also trigger the prefetch for the next page on the way up.
    goToTop();

    if (pagesSeen.includes(page + 1)) {
      return setPage(page + 1);
    }

    if (prefetchedOrders) {
      const allOrders = orders.concat(prefetchedOrders);
      setOrders(allOrders);
      setPage(page + 1);
      setPagesSeen([...pagesSeen, page + 1]);
      setPrefetchedOrders(null);
      return;
    }

    setIsLoading(true);
  };

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