我有一个正在运行的加载组件，它在加载 8 秒后取消。这段代码有效，但对我来说感觉不对，我想知道是否有更好的方法来做到这一点。

没有设置 this.mounted 我得到错误:

Warning: Can only update a mounted or mounting component. This usually means you called setState, replaceState, or forceUpdate on an unmounted component. This is a no-op. Please check the code for the Loading component.

这让我觉得计时器没有被取消，所以它继续 this.seState。如果我在 componentWillUnmount 中设置 clearTimeout 为什么会这样？有没有比使用全局 this.mounted 更好的方法来处理这个问题？

class Loading extends Component {
  state = {
    error: false,
  };

  componentDidMount = () => {
    this.mounted = true;
    this.timer();
  };

  componentWillUnmount = () => {
    this.mounted = false;
    clearTimeout(this.timer);
  };

  timer = () =>
    setTimeout(() => {
      (this.mounted && this.setState({ error: true })) || null;
    }, 8000);

  render() {
    const { showHeader = false } = this.props;
    const { error } = this.state;
    return (
      <View style={backgroundStyle}>
        {showHeader && <HeaderShell />}
        {!error &&
          <View style={loadingHeight}>
            <PlatformSpinner size="large" />
          </View>}
        {error && <Error code="service" />}
      </View>
    );
  }
}

Loading.propTypes = {
  showHeader: PropTypes.bool,
};

Loading.defaultProps = {
  showHeader: false,
};

export default Loading;

最佳答案

This make me think that the timer is not getting canceled

正如 Pointy 所说，事实并非如此。您正在将一个函数 (this.timer) 传递到clearTimeout。您需要传递 setTimeout 返回值(计时器的句柄)，以便您可以使用该句柄来取消它。

在这样一个简单的组件中，我看不到需要 timer 功能，它只会增加复杂性；我只是在 CDM 中设置计时器:

class Loading extends Component {
  state = {
    error: false,
  };

  componentDidMount = () => {                // ***
    // Remember the timer handle             // ***
    this.timerHandle = setTimeout(() => {    // ***
      this.setState({ error: true });        // ***
      this.timerHandle = 0;                  // ***
    }, 8000);                                // ***
  };                                         // ***
                                             // ***
  componentWillUnmount = () => {             // ***
    // Is our timer running?                 // ***
    if (this.timerHandle) {                  // ***
        // Yes, clear it                     // ***
        clearTimeout(this.timerHandle);      // ***
        this.timerHandle = 0;                // ***
    }                                        // ***
  };                                         // ***

  render() {
    const { showHeader = false } = this.props;
    const { error } = this.state;
    return (
      <View style={backgroundStyle}>
        {showHeader && <HeaderShell />}
        {!error &&
          <View style={loadingHeight}>
            <PlatformSpinner size="large" />
          </View>}
        {error && <Error code="service" />}
      </View>
    );
  }
}

Loading.propTypes = {
  showHeader: PropTypes.bool,
};

Loading.defaultProps = {
  showHeader: false,
};

export default Loading;

但是如果有比显示更多的逻辑，或者只是个人喜好，是的，单独的函数是好的:

class Loading extends Component {
  state = {
    error: false,
  };

  componentDidMount = () => {
    this.setTimer();
  };

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

  setTimer = () => {
    if (this.timerHandle) {
      // Exception?
      return;
    }
    // Remember the timer handle
    this.timerHandle = setTimeout(() => {
      this.setState({ error: true });
      this.timerHandle = 0;
    }, 8000);
  };

  clearTimer = () => {
    // Is our timer running?
    if (this.timerHandle) {
        // Yes, clear it
        clearTimeout(this.timerHandle);
        this.timerHandle = 0;
    }
  };

  render() {
    const { showHeader = false } = this.props;
    const { error } = this.state;
    return (
      <View style={backgroundStyle}>
        {showHeader && <HeaderShell />}
        {!error &&
          <View style={loadingHeight}>
            <PlatformSpinner size="large" />
          </View>}
        {error && <Error code="service" />}
      </View>
    );
  }
}

Loading.propTypes = {
  showHeader: PropTypes.bool,
};

Loading.defaultProps = {
  showHeader: false,
};

export default Loading;

关于javascript - 在 componentWillUnmount 中清除超时的更好方法，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/45678517/