反应：是否可以通过将this.setState设置为空函数来防止卸载后的状态更新？

Question

I am facing the problem that a network callback is trying to setState() of an unmounted component and receive the default console warning about this no-op.

It wasn't possible for me to track why the unmount happens but I found a solution suggesting to set the function to nothing in componentWillUnmount(). It didn't work and I tested to set this.setState to nothing. See below.

The error disappears but I want to ask whether that is a valid solution. Here the code:

  componentDidMount() {
    this.fetchLogItems(10, 'recentChanges');
  }

  componentWillUnmount() {
    this.setState = () => {};
  }

  fetchLogItems = (limit, stateRef) => {
    let tmpObj = {};
    base.fetch('_changelogs', {
      context: this,
      then(data) {
        tmpObj[stateRef] = {...data}
        tmpObj.loading = false;
        this.setState({...tmpObj})
      },
      catch(err){console.error(err)}
    });
  };

Answer 1

Two options:

• be sure that whatever helpers that you are using also allow for the use of "destructors" (cancellations, and I definitely prefer the use of "cancellations")
• if not, then you may introduce a "flag" to your class

If your library allows for some "cancellation", "destruction", or "cleanup", then you may simply do:

componentWillUnmount() {
  base.cancelFetch(); // or something similar.
}

Otherwise, you may be able to introduce a class property to your component. Perhaps name it isUnmounted . In componentWillUnmount , set this.isUmounted to true. Wrap the this.setState call in an if -statement that checks if isUnmounted is false, and if it is, then you may call this.setState . This is actually a very common pattern.

It may " feel " ugly, but, by defacto, this pattern seems to be idiomatic among React developers. If not, at least it is a pragmatic solution to problems similar to yours.

constructor() {
  // HERE
  this.isUmounted = false;
}

componentDidMount() {
  this.fetchLogItems(10, 'recentChanges');
}

componentWillUnmount() {
  // HERE
  this.isUmounted = true;
}

fetchLogItems = (limit, stateRef) => {
  let tmpObj = {};
  base.fetch('_changelogs', {
    context: this,
    then(data) {
      tmpObj[stateRef] = {...data}
      tmpObj.loading = false;
      // WRAP THE `this.setState` here.
      if (!this.isUnmounted) {
        this.setState({...tmpObj})
      }
    },
    catch(err){console.error(err)}
  });
};

However, I prefer the use of libraries and helpers that support cancellation. It's definitely guarantees some level of cleanup. Without cancellation, we risk introducing memory leaks.