在 componentWillUnmount 方法中取消所有订阅和异步，如何？

Question

由于异步方法问题，我收到一条错误消息。在我的终端中，我看到：

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.
- node_modules/fbjs/lib/warning.js:33:20 in printWarning
- node_modules/fbjs/lib/warning.js:57:25 in warning
- node_modules/react-native/Libraries/Renderer/ReactNativeRenderer-dev.js:12196:6 in warnAboutUpdateOnUnmounted
- node_modules/react-native/Libraries/Renderer/ReactNativeRenderer-dev.js:13273:41 in scheduleWorkImpl
- node_modules/react-native/Libraries/Renderer/ReactNativeRenderer-dev.js:6224:19 in enqueueSetState
- node_modules/react/cjs/react.development.js:242:31 in setState
* router/_components/item.js:51:16 in getImage$
- node_modules/regenerator-runtime/runtime.js:62:44 in tryCatch
- node_modules/regenerator-runtime/runtime.js:296:30 in invoke
- ... 13 more stack frames from framework internals

我注意到它特别指出 getImage$

这是我在该部分使用的代码：

export default class extends Component {
    constructor(props) {
        super(props);
        const { item } = props

        const bindThese = { item }
        this.boundActionCreators = bindActionCreators(bindThese)

        this.state = {
            image: require('../../static/logo.png'),
            ready: false,
            showOptions: this.props.showOptions
        }

        this.getImage = this.getImage.bind(this)
        this.renderNotAdmin = this.renderNotAdmin.bind(this)
        this.renderAdmin = this.renderAdmin.bind(this)
        this.handleOutOfStock = this.handleOutOfStock.bind(this)
    }

    async getImage(img) {
        let imgUri = await Amplify.Storage.get(img)
        let uri = await CacheManager.get(imgUri).getPath()

        this.setState({
            image: { uri },
            ready: true
        })
    }

    componentDidMount() {
        this.getImage(this.props.item.image)
    }

我正在尝试弄清楚如何将 componentWillUnmount 与此异步方法一起使用。我该怎么做？

谢谢！

Answer 1

来自React blog

Just set a _isMounted property to true in componentDidMount and set it to false in componentWillUnmount, and use this variable to check your component’s status.

它接着说，理想情况下，这将通过使用可取消的回调来解决，尽管第一个解决方案在这里似乎合适。

您绝对不应该使用 isMounted() 函数，该函数可能已被弃用。

Answer 2

您可以使用 isMounted React 模式来避免此处的内存泄漏。

在你的构造函数中：

constructor(props) {
    super(props);

    this._isMounted = false;
// rest of your code
}

componentDidMount() {
    this._isMounted = true;
    this._isMounted && this.getImage(this.props.item.image);

}

在你的 componentWillUnmount

componentWillUnmount() {
   this._isMounted = false;
}

在你身上getImage()

async getImage(img) {
    let imgUri = await Amplify.Storage.get(img)
    let uri = await CacheManager.get(imgUri).getPath()

    this._isMounted && this.setState({
        image: { uri },
        ready: true
    })
}

使用基于可取消承诺模式的 Axios 的推荐方法。因此，您可以在使用 cancelToken subscription 卸载组件时取消任何网络调用。这是 Axios Cancellation

的资源

Answer 3

您需要在 componentWillUnmount() 方法中设置 this.mounted = false，在 componentDidMount() 方法中设置 this.mounted = true。

setState更新是有条件的，需要在componentDidMount()方法中声明。

componentDidMount() {
        this.mounted = true;
        var myVar =  setInterval(() => {
                let nextPercent = this.state.percentage+10;
                if (nextPercent >= 100) {
                    clearInterval(myVar);
                }
                if(this.mounted) {
                    this.setState({ percentage: nextPercent });
            }
        }, 100);
}

componentWillUnmount(){
      this.mounted = false;
}

Answer 4

我通过覆盖 setState 方法解决了错误

isSubscribed = true;

componentWillUnmount() {
  this.isSubscribed = false;
}

setState = (state, callback?) => {
   if (this.isSubscribed) {
     super.setState(state, callback);
   }
}

在 componentWillUnmount 方法中取消所有订阅和异步，如何？

Cancel All Subscriptions and Asyncs in the componentWillUnmount Method, how?

javascript

lifecycle

node.js

reactjs

react-native