0

情况

  • 我想根据图像的高度重新分配网格（使用砌体方法）
  • 这些图像是延迟加载的

我想要的是

  • 加载图像时，它们会发送一个标志，该标志使砌体逻辑重新分配网格，每个人都很高兴
  • 然后当用户滚动时，加载更多图像，再次触发标志，砌体再次调整网格

怎么了

*const [myState, setMyState] = use State(0)

  • 加载图像时，我setMyState(1)
  • 在砌体逻辑中，我有一个useLayoutEffect(() =>{}, [myState])所以当状态改变时，我调整网格
  • 然后我用 重置状态setMyState(0)，这样当加载新图像时它会再次触发useLayoutEffect
  • 但是，当我重置状态时，它会重新绘制图像，因此图像会再次加载并再次触发useLayoutEffect，这会再次重置状态，从而创建无限循环
  • 如果我不重置状态，则循环停止
  • 但是，当使用滚动加载新图像时，setMyState(1)不会更改任何内容并且useLayoutEffect不会触发

所以我现在卡住了

这是一个简化的代码

import React, { useRef, useLayoutEffect, useState} from "react";

const wait = ms =>
  new Promise((res, rej) => setTimeout(() => res("timed"), ms));

const Image = ({ setImageLoader }) => {
  // lazy load the image with an Observer, and then changes the state
  setImageLoader(1);
  return <></>;
};

export default function App() {
  const [imageLoaded, setImageLoader] = useState(0);

  useLayoutEffect(() => {
    const update_grid = async stillMounted => {
      // change stuff
      await wait(10000); // careful with crashing chrome
      console.log("updated");
      setImageLoader(0);
    };

    const stillMounted = { value: true };
    update_grid(stillMounted);
    return () => (stillMounted.value = false);
  }, [imageLoaded]);

  return <Image setImageLoader={setImageLoader} />;
}

尝试 1

我无法更改 中的状态useLayoutEffect，所以我只会在加载图像时更改内容，而不是再次更改

问题

当我滚动并加载更多图像时，我无法再触发 useLayoutEffect

import React, { useRef, useLayoutEffect, useState} from "react";

const wait = ms =>
  new Promise((res, rej) => setTimeout(() => res("timed"), ms));

const Image = ({ setImageLoader }) => {
  setImageLoader(1);
  return <>hey</>;
};

export default function App() {
  const [imageLoaded, setImageLoader] = useState(0);

  useLayoutEffect(() => {
    // change stuff
    const update_grid = async stillMounted => {
      await wait(40000);
      console.log("updated");
      // setImageLoader(0); NOW THIS IS NOT CAUSING THE REPAINT, BUT NEITHER WHEN NEW IMAGES ARE LOADED
    };

    const stillMounted = { value: true };
    update_grid(stillMounted);
    return () => (stillMounted.value = false);
  }, [imageLoaded]);

  return <Image setImageLoader={setImageLoader} />;
}

尝试 2

如果我不想重绘，但想触发 useLayoutEffect，我可以使用useRef而不是useState

import React, { useRef, useLayoutEffect, useState, useEffect } from "react";

const wait = ms =>
  new Promise((res, rej) => setTimeout(() => res("timed"), ms));

const Image = ({ imageLoaded }) => {
  imageLoaded.current++;
  return <>hey</>;
};

export default function App() {
  const imageLoaded = useRef(0);

  useLayoutEffect(() => {
    // change stuff
    const update_grid = async stillMounted => {
      await wait(10000);
      console.log("updated " + imageLoaded.current);
      imageLoaded.current++;
    };

    const stillMounted = { value: true };
    update_grid(stillMounted);
    return () => (stillMounted.value = false);
  }, [imageLoaded.current]);

  return <Image imageLoaded={imageLoaded} />;
}

但是codeandbox已经警告我imageLoaded.current不会导致组件的重新渲染（即使我或多或少想要这个？）

所以最后，我看到imageLoaded.current加载新图像时增加，但useLayoutEffect没有触发

4

1 回答 1

0

我无法使用useEffect或类似方法解决该问题

相反，我使用了一个简单的函数来调整网格，并在加载图像时从延迟加载逻辑中调用它

import React, { useRef, useEffect, useState } from "react";

const wait = ms =>
  new Promise((res, rej) => setTimeout(() => res("timed"), ms));

const Image = ({ adjustMasonry }) => {
  // lazy load the image with an Observer, and then changes the state
  const scroll = async () => {
    adjustMasonry();
    adjustMasonry(); // only causes one update due to the implemented buffer
    await wait(4000);
    adjustMasonry();
  };
  scroll();
  return <></>;
};

export default function App() {
  let signals = 0;
  const adjustMasonry = async stillMounted => {
    signals++;
    const last_signal = signals;
    await wait(200); // careful with crashing chrome
    if (signals !== last_signal) return; // as a way to minimize the number of consecutive calls
    if (stillMounted && !stillMounted.value) return;

    // change stuff
    console.log("updated");
  };

  useEffect(() => {
    const stillMounted = { value: true };
    adjustMasonry(stillMounted);

    return () => {
      stillMounted.value = false;
    };
  }, []);

  return <Image adjustMasonry={adjustMasonry} />;
}
于 2020-01-31T10:18:25.280 回答