React useEffect causing: Can't perform a React state update on an unmounted component

问题

When fetching data I'm getting: Can't perform a React state update on an unmounted component. The app still works, but react is suggesting I might be causing a memory leak.

"This is a no-op, but it indicates a memory leak in your application. To fix, cancel all subscriptions and asynchronous tasks in a useEffect cleanup function."

Why do I keep getting this warning?

I tried researching these solutions:

https://developer.mozilla.org/en-US/docs/Web/API/AbortSignal

https://developer.mozilla.org/en-US/docs/Web/API/AbortController

but this still was giving me the warning.

const  ArtistProfile = props => {
  const [artistData, setArtistData] = useState(null)
  const token = props.spotifyAPI.user_token

  const fetchData = () => {
    const id = window.location.pathname.split("/").pop()
    console.log(id)
    props.spotifyAPI.getArtistProfile(id, ["album"], "US", 10)
    .then(data => {setArtistData(data)})
  }
  useEffect(() => {
    fetchData()
    return () => { props.spotifyAPI.cancelRequest() }
  }, [])

  return (
    <ArtistProfileContainer>
      <AlbumContainer>
        {artistData ? artistData.artistAlbums.items.map(album => {
          return (
            <AlbumTag
              image={album.images[0].url}
              name={album.name}
              artists={album.artists}
              key={album.id}
            />
          )
        })
        : null}
      </AlbumContainer>
    </ArtistProfileContainer>
  )
}

Edit:

In my api file I added an AbortController() and used a signal so I can cancel a request.

export function spotifyAPI() {
  const controller = new AbortController()
  const signal = controller.signal

// code ...

  this.getArtist = (id) => {
    return (
      fetch(
        `https://api.spotify.com/v1/artists/${id}`, {
        headers: {"Authorization": "Bearer " + this.user_token}
      }, {signal})
      .then(response => {
        return checkServerStat(response.status, response.json())
      })
    )
  }

  // code ...

  // this is my cancel method
  this.cancelRequest = () => controller.abort()
}

My spotify.getArtistProfile() looks like this

this.getArtistProfile = (id,includeGroups,market,limit,offset) => {
  return Promise.all([
    this.getArtist(id),
    this.getArtistAlbums(id,includeGroups,market,limit,offset),
    this.getArtistTopTracks(id,market)
  ])
  .then(response => {
    return ({
      artist: response[0],
      artistAlbums: response[1],
      artistTopTracks: response[2]
    })
  })
}

but because my signal is used for individual api calls that are resolved in a Promise.all I can't abort() that promise so I will always be setting the state.

回答1:

Sharing the AbortController between the fetch() requests is the right approach.
When any of the Promises are aborted, Promise.all() will reject with AbortError:

function Component(props) {
  const [fetched, setFetched] = React.useState(false);
  React.useEffect(() => {
    const ac = new AbortController();
    Promise.all([
      fetch('http://placekitten.com/1000/1000', {signal: ac.signal}),
      fetch('http://placekitten.com/2000/2000', {signal: ac.signal})
    ]).then(() => setFetched(true))
      .catch(ex => console.error(ex));
    return () => ac.abort(); // Abort both fetches on unmount
  }, []);
  return fetched;
}
const main = document.querySelector('main');
ReactDOM.render(React.createElement(Component), main);
setTimeout(() => ReactDOM.unmountComponentAtNode(main), 1); // Unmount after 1ms

<script src="//cdnjs.cloudflare.com/ajax/libs/react/16.8.3/umd/react.development.js"></script>
<script src="//cdnjs.cloudflare.com/ajax/libs/react-dom/16.8.3/umd/react-dom.development.js"></script>
<main></main>

回答2:

You can try this set a state like this and check if your component mounted or not. This way you are sure that if your component is unmounted you are not trying to fetch something.

const [didMount, setDidMount] = useState(false); 

useEffect(() => {
   setDidMount(true);
   return () => setDidMount(false);
}, [])

if(!didMount) {
  return null;
}

return (
    <ArtistProfileContainer>
      <AlbumContainer>
        {artistData ? artistData.artistAlbums.items.map(album => {
          return (
            <AlbumTag
              image={album.images[0].url}
              name={album.name}
              artists={album.artists}
              key={album.id}
            />
          )
        })
        : null}
      </AlbumContainer>
    </ArtistProfileContainer>
  )

Hope this will help you.

来源：https://stackoverflow.com/questions/54954385/react-useeffect-causing-cant-perform-a-react-state-update-on-an-unmounted-comp