javascript - 无法对已卸载的组件调用 setState(或forceUpdate)

Question

我试图在组件更新后从服务器获取数据，但我无法做到这一点。据我了解，当组件即将被销毁时，会调用 componentWillUnmount ，但我永远不需要销毁它，所以它对我来说毫无用处。对此有什么解决方案？我什么时候应该设置状态？

async componentDidUpdate(prevProps, prevState) {
  if (this.props.subject.length && prevProps.subject !== this.props.subject) {
    let result = await this.getGrades({
      student: this.props.id,
      subject: this.props.subject
    });
    this.setState({
      subject: this.props.subject,
      grades: result
    });
  }
}

async getGrades(params) {
  let response, body;

  if (params['subject'].length) {
    response = await fetch(apiRequestString.gradesBySubject(params));
    body = await response.json();
  } else {
    response = await fetch(apiRequestString.grades(params));
    body = await response.json();
  }

  if (response.status !== 200) throw Error(body.message);

  return body;
}

完整错误:

Warning: Can't call setState (or forceUpdate) on an unmounted component. This is a no-op, 
but it indicates a memory leak in your application. To fix, cancel all subscriptions and
asynchronous tasks in the componentWillUnmount method.

Answer 1

我在本例中使用的常见模式类似于

componentWillUnmount() {
    this.isCancelled = true;
}

然后在等待异步函数解析的代码中，您可以在设置状态之前添加检查:

async componentDidUpdate(prevProps, prevState) {
    if (this.props.subject.length && prevProps.subject !== this.props.subject) {
        let result = await this.getGrades({
            student: this.props.id,
            subject: this.props.subject
        });
        !this.isCancelled && this.setState({
            subject: this.props.subject,
            grades: result
        });
    }
}

这将停止未安装/卸载组件上的任何状态设置