React挂钩-清除超时和间隔的正确方法

小编典典

React挂钩-清除超时和间隔的正确方法

reactjs

我不明白为什么当我使用setTimeout函数时，我的react组件开始进入无限console.log。一切正常，但PC开始陷入困境。有人说超时中的功能会更改我的状态，并会重新渲染组件，设置新的计时器等。现在，我需要了解如何清除它是正确的。

export default function Loading() {
  // if data fetching is slow, after 1 sec i will show some loading animation
  const [showLoading, setShowLoading] = useState(true)
  let timer1 = setTimeout(() => setShowLoading(true), 1000)

  console.log('this message will render  every second')
  return 1
}

清除不同版本的代码无法帮助：

const [showLoading, setShowLoading] = useState(true)
  let timer1 = setTimeout(() => setShowLoading(true), 1000)
  useEffect(
    () => {
      return () => {
        clearTimeout(timer1)
      }
    },
    [showLoading]
  )

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2020-07-22

共1个答案

小编典典

__useEffect 每次运行时useEffect都会在运行中返回
函数（首次运行在组件安装上除外）。考虑一下它，因为每次useEffect执行新的执行时，旧的执行都会被删除。

这是使用和清除超时或间隔的一种有效方法：

export default function Loading() {   
     const [showLoading, setShowLoading] = useState(false)

     useEffect(
        () => {
          let timer1 = setTimeout(() => setShowLoading(true), 1000)

          // this will clear Timeout when component unmount like in willComponentUnmount
          return () => {
            clearTimeout(timer1)
          }
        },
        [] //useEffect will run only one time
           //if you pass a value to array, like this [data] than clearTimeout will run every time this value changes (useEffect re-run)
      )

 return showLoading && <div>I will be visible after ~1000ms</div>
}

如果您需要清除超时或间隔时间不在某个地方：

export default function Loading() {   
     const [showLoading, setShowLoading] = useState(false)

     const timerToClearSomewhere = useRef(false) //now you can pass timer to another component

     useEffect(
        () => {
          timerToClearSomewhere.current = setInterval(() => setShowLoading(true), 50000)

          return () => {
            clearInterval(timerToClearSomewhere.current)
          }
        },
        []
      )

  //here we can imitate clear from somewhere else place
  useEffect(() => {
    setTimeout(() => clearInterval(timerToClearSomewhere.current), 1000)
  }, [])

 return showLoading ? <div>I will never be visible because interval was cleared</div> : <div>showLoading is false</div>
}

2020-07-22