如何在 useEffect 中向 useRef 添加事件侦听器 [英] How to add an event listener to useRef in useEffect

问题描述

我正在构建一个自定义钩子，我想在其中向 ref 添加一个事件侦听器，但我不确定如何正确清理，因为 listRef 和 listRef.current 可以为空:

export const myHook: MyHook = () =>{const listRef = useRef(null)useEffect(() => {//我可以在这里检查 `listRef.current` 是否存在 ...如果(listRef && listRef.current){listRef.current.addEventListener(...)}//...但是返回函数的正确方法是什么?返回 listRef.current.removeEventListener(...)})返回 [listRef]}

解决方案

<块引用>

但我也必须检查返回函数中是否存在 listRef ，对吗?

是的，您可以做的是将所有内容都包裹在 if 语句中

 useEffect(() => {//if 语句周围的一切如果(listRef && listRef.current){listRef.current.addEventListener(...)返回 () =>{listRef.current.removeEventListener(...)}}})

如果你不调用addEventListener，你就不需要调用removeEventListener，所以这就是为什么你把所有的东西都放在if.

<小时>

您需要在 return 中传递一个函数来执行您在清理中想做的事情.

export const myHook: MyHook = () =>{const listRef = useRef(null)useEffect(() => {//还行吧如果(listRef && listRef.current){listRef.current.addEventListener(...)}//传递一个调用你的函数的函数返回 () =>{listRef.current.removeEventListener(...)}})返回 [listRef]}

你需要注意的另一件事是在fooEventListener中，...应该是函数的相同引用，这意味着:

你不应该这样做:

 useEffect(() => {如果(listRef && listRef.current){listRef.current.addEventListener(() => console.log('do something'))}返回 () =>{listRef.current.removeEventListener(() => console.log('do something'))}})

你应该这样做:

 useEffect(() => {const myFunction = () =>console.log('做某事')如果(listRef && listRef.current){//传递相同的引用listRef.current.addEventListener(myFunction)}返回 () =>{//传递相同的引用listRef.current.removeEventListener(myFunction)}})

I'm building a custom hook where I want to add an event listener to a ref, but I'm not sure how to clean up properly, since listRef and listRef.current could be null:

export const myHook: MyHook = () => {
  const listRef = useRef<HTMLDivElement>(null)

  useEffect(() => {
    // I can check for the presence of `listRef.current` here ...
    if (listRef && listRef.current) {
      listRef.current.addEventListener(...)
    }

    // ... but what's the right way for the return function?
    return listRef.current.removeEventListener(...)
  })

  return [listRef]
}

解决方案

Edit:

but I have to check for the presence of listRef in the return function too, right?

Yes, and what you could do is wrap everythinig around the if statement

  useEffect(() => {
    // Everything around if statement
    if (listRef && listRef.current) {
      listRef.current.addEventListener(...)

      return () => {
        listRef.current.removeEventListener(...)
      }
    }
  })

If you don't call addEventListener, you don't need to call removeEventListener, so that is why you put everything inside the if.

---

You need to pass a function in the return that do what you want to do in the cleanup.

export const myHook: MyHook = () => {
  const listRef = useRef<HTMLDivElement>(null)

  useEffect(() => {
    // This is ok
    if (listRef && listRef.current) {
      listRef.current.addEventListener(...)
    }

    // Passing a function that calls your function
    return () => {
        listRef.current.removeEventListener(...)
    }
  })

  return [listRef]
}

Another thing you need to notice is that inside the fooEventListener, the ... should be the same reference of the function, this means:

You shoudn't do this:

  useEffect(() => {
    if (listRef && listRef.current) {
      listRef.current.addEventListener(() => console.log('do something'))
    }

    return () => {
        listRef.current.removeEventListener(() => console.log('do something'))
    }
  })

And you should do :

  useEffect(() => {
    const myFunction = () => console.log('do something')

    if (listRef && listRef.current) {
      // Passing the same reference
      listRef.current.addEventListener(myFunction)
    }

    return () => {
      // Passing the same reference
      listRef.current.removeEventListener(myFunction)
    }
  })

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