Question

我正在使用以下代码（useEffect）更改滚动类。

import { useState, useEffect } from "react"

export const useScrollHandler = () => {
  // setting initial value to true
  const [scroll, setScroll] = useState(1)

  // running on mount
  useEffect(() => {
    const onScroll = () => {
      const scrollCheck = window.scrollY < 10
      if (scrollCheck !== scroll) {
        setScroll(scrollCheck)
      }
    }

    // setting the event handler from web API

    document.addEventListener("scroll", onScroll)

    // cleaning up from the web API
    return () => {
      document.removeEventListener("scroll", onScroll)
    }
  }, [scroll, setScroll])
  return scroll
}

即使我使用了清理功能，执行history.push（“ /”）时也会出现以下错误

警告：无法在已卸载的组件上执行React状态更新。这是空操作，但它表明应用程序中发生内存泄漏。要修复，请取消使用useEffect清理功能中的所有订阅和异步任务。

如何解决？

这里我用过useScrollHandler。

function HomeNav() {
  const scroll = useScrollHandler()
  return (
    <React.Fragment>
      <nav
        className={
          scroll ? "navbar navbar-expand-lg navbar-light fixed-top py-3" : "navbar navbar-expand-lg navbar-light fixed-top py-3 navbar-scrolled"
        }
        id="mainNav"
      >
      </nav>
    </React.Fragment>
  )
}

export default HomeNav

Answer 1

请尝试删除EventListener上的unmount。

const onScroll = () => {
      const scrollCheck = window.scrollY < 10
      if (scrollCheck !== scroll) {
        setScroll(scrollCheck)
      }
}

useEffect(() => {

    // Add event listener on component mount
    document.addEventListener("scroll", onScroll)

    // removing event listener on component unmount
    return () => {
      document.removeEventListener("scroll", onScroll)
    }
}, []) // This useEffect will act as componentDidMount and return function as componentWillUnmount as no dependencies are given.

Answer 2

我认为您不需要在事件处理程序中使用scroll，并且可以保证setScroll 保持不变，这意味着效果处理程序可以使用[]作为其依赖项数组。简化可能会有所帮助。

import { useState, useEffect } from "react"

export const useScrollHandler = () => {
  // setting initial value to true
  const [scroll, setScroll] = useState(true);
  // running on mount
  useEffect(() => {
    const onScroll = () => setScroll(window.scrollY < 10)
    // setting the event handler from web API
    document.addEventListener("scroll", onScroll)
    // cleaning up from the web API
    return () => {
      document.removeEventListener("scroll", onScroll)
    }
  }, [])
  return scroll
}

无法在未安装的组件上执行React状态更新（useEffect react挂钩）

2 个答案: