Code
2023-11-17 06:00:04

不能在未挂载的组件上执行React状态更新

问题

我正在React中编写一个应用程序，无法避免一个超级常见的陷阱，即在componentWillUnmount(…)之后调用setState(…)。

我非常仔细地查看了我的代码，并试图在适当的位置放置一些保护子句，但问题仍然存在，我仍然观察到警告。

因此，我有两个问题:

我如何从堆栈跟踪中找出哪个特定的组件和事件处理程序或生命周期钩子对违反规则负责? 好吧，如何修复问题本身，因为我的代码在编写时就考虑到了这个陷阱，并且已经试图防止它，但一些底层组件仍然生成警告。

浏览器控制台

Warning: Can't perform a React state update 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.
    in TextLayerInternal (created by Context.Consumer)
    in TextLayer (created by PageInternal) index.js:1446
d/console[e]
index.js:1446
warningWithoutStack
react-dom.development.js:520
warnAboutUpdateOnUnmounted
react-dom.development.js:18238
scheduleWork
react-dom.development.js:19684
enqueueSetState
react-dom.development.js:12936
./node_modules/react/cjs/react.development.js/Component.prototype.setState
react.development.js:356
_callee$
TextLayer.js:97
tryCatch
runtime.js:63
invoke
runtime.js:282
defineIteratorMethods/</prototype[method]
runtime.js:116
asyncGeneratorStep
asyncToGenerator.js:3
_throw
asyncToGenerator.js:29

Code

Book.tsx

import { throttle } from 'lodash';
import * as React from 'react';
import { AutoWidthPdf } from '../shared/AutoWidthPdf';
import BookCommandPanel from '../shared/BookCommandPanel';
import BookTextPath from '../static/pdf/sde.pdf';
import './Book.css';

const DEFAULT_WIDTH = 140;

class Book extends React.Component {
  setDivSizeThrottleable: () => void;
  pdfWrapper: HTMLDivElement | null = null;
  isComponentMounted: boolean = false;
  state = {
    hidden: true,
    pdfWidth: DEFAULT_WIDTH,
  };

  constructor(props: any) {
    super(props);
    this.setDivSizeThrottleable = throttle(
      () => {
        if (this.isComponentMounted) {
          this.setState({
            pdfWidth: this.pdfWrapper!.getBoundingClientRect().width - 5,
          });
        }
      },
      500,
    );
  }

  componentDidMount = () => {
    this.isComponentMounted = true;
    this.setDivSizeThrottleable();
    window.addEventListener("resize", this.setDivSizeThrottleable);
  };

  componentWillUnmount = () => {
    this.isComponentMounted = false;
    window.removeEventListener("resize", this.setDivSizeThrottleable);
  };

  render = () => (
    <div className="Book">
      { this.state.hidden && <div className="Book__LoadNotification centered">Book is being loaded...</div> }

      <div className={this.getPdfContentContainerClassName()}>
        <BookCommandPanel
          bookTextPath={BookTextPath}
          />

        <div className="Book__PdfContent" ref={ref => this.pdfWrapper = ref}>
          <AutoWidthPdf
            file={BookTextPath}
            width={this.state.pdfWidth}
            onLoadSuccess={(_: any) => this.onDocumentComplete()}
            />
        </div>

        <BookCommandPanel
          bookTextPath={BookTextPath}
          />
      </div>
    </div>
  );

  getPdfContentContainerClassName = () => this.state.hidden ? 'hidden' : '';

  onDocumentComplete = () => {
    try {
      this.setState({ hidden: false });
      this.setDivSizeThrottleable();
    } catch (caughtError) {
      console.warn({ caughtError });
    }
  };
}

export default Book;

AutoWidthPdf.tsx

import * as React from 'react';
import { Document, Page, pdfjs } from 'react-pdf';

pdfjs.GlobalWorkerOptions.workerSrc = `//cdnjs.cloudflare.com/ajax/libs/pdf.js/${pdfjs.version}/pdf.worker.js`;

interface IProps {
  file: string;
  width: number;
  onLoadSuccess: (pdf: any) => void;
}
export class AutoWidthPdf extends React.Component<IProps> {
  render = () => (
    <Document
      file={this.props.file}
      onLoadSuccess={(_: any) => this.props.onLoadSuccess(_)}
      >
      <Page
        pageNumber={1}
        width={this.props.width}
        />
    </Document>
  );
}

更新1:取消可节流功能(仍然没有运气)

const DEFAULT_WIDTH = 140;

class Book extends React.Component {
  setDivSizeThrottleable: ((() => void) & Cancelable) | undefined;
  pdfWrapper: HTMLDivElement | null = null;
  state = {
    hidden: true,
    pdfWidth: DEFAULT_WIDTH,
  };

  componentDidMount = () => {
    this.setDivSizeThrottleable = throttle(
      () => {
        this.setState({
          pdfWidth: this.pdfWrapper!.getBoundingClientRect().width - 5,
        });
      },
      500,
    );

    this.setDivSizeThrottleable();
    window.addEventListener("resize", this.setDivSizeThrottleable);
  };

  componentWillUnmount = () => {
    window.removeEventListener("resize", this.setDivSizeThrottleable!);
    this.setDivSizeThrottleable!.cancel();
    this.setDivSizeThrottleable = undefined;
  };

  render = () => (
    <div className="Book">
      { this.state.hidden && <div className="Book__LoadNotification centered">Book is being loaded...</div> }

      <div className={this.getPdfContentContainerClassName()}>
        <BookCommandPanel
          BookTextPath={BookTextPath}
          />

        <div className="Book__PdfContent" ref={ref => this.pdfWrapper = ref}>
          <AutoWidthPdf
            file={BookTextPath}
            width={this.state.pdfWidth}
            onLoadSuccess={(_: any) => this.onDocumentComplete()}
            />
        </div>

        <BookCommandPanel
          BookTextPath={BookTextPath}
          />
      </div>
    </div>
  );

  getPdfContentContainerClassName = () => this.state.hidden ? 'hidden' : '';

  onDocumentComplete = () => {
    try {
      this.setState({ hidden: false });
      this.setDivSizeThrottleable!();
    } catch (caughtError) {
      console.warn({ caughtError });
    }
  };
}

export default Book;

当前回答

我通过提供useEffect钩子中使用的所有参数来解决这个问题

代码报告了该错误:

useEffect(() => {
    getDistrict({
      geonameid: countryId,
      subdistrict: level,
    }).then((res) => {
      ......
    });
  }, [countryId]);

修复后的代码:

useEffect(() => {
    getDistrict({
      geonameid: countryId,
      subdistrict: level,
    }).then((res) => {
      ......
    });
  }, [countryId,level]);

可以看到，问题解决后，我提供了所有的参数(包括水平参数)，应该通过。

2021-07-27 02:47:38

其他回答

我通过提供useEffect钩子中使用的所有参数来解决这个问题

代码报告了该错误:

useEffect(() => {
    getDistrict({
      geonameid: countryId,
      subdistrict: level,
    }).then((res) => {
      ......
    });
  }, [countryId]);

修复后的代码:

useEffect(() => {
    getDistrict({
      geonameid: countryId,
      subdistrict: level,
    }).then((res) => {
      ......
    });
  }, [countryId,level]);

可以看到，问题解决后，我提供了所有的参数(包括水平参数)，应该通过。

2021-07-27 02:47:38

根据React文档，检查组件是否被挂载实际上是一个反模式。setState警告的解决方案是利用AbortController的使用:

useEffect(() => {
  const abortController = new AbortController()   // creating an AbortController
  fetch(url, { signal: abortController.signal })  // passing the signal to the query
    .then(data => {
      setState(data)                              // if everything went well, set the state
    })
    .catch(error => {
      if (error.name === 'AbortError') return     // if the query has been aborted, do nothing
      throw error
    })
  
  return () => {
    abortController.abort()                       // stop the query by aborting on the AbortController on unmount
  }
}, [])

对于不基于Fetch API的异步操作，仍然应该有一种方法来取消这些异步操作，您应该利用这些操作，而不仅仅是检查组件是否被挂载。如果您正在构建自己的API，您可以在其中实现AbortController API来处理它。

更详细地说，检查组件是否被挂载是一个反模式，因为React在内部检查组件是否被挂载以显示警告。再次执行相同的检查只是隐藏警告的一种方法，还有一些更简单的方法来隐藏警告，而不是将这段代码添加到代码库的大部分中。

来源:https://medium.com/doctolib/react-stop-checking-if-your-component-is-mounted-3bb2568a4934

2021-10-07 16:41:32

这里有一个简单的解决方案。这个警告是由于当我们在后台执行一些取回请求时(因为一些请求需要一些时间)，我们从那个屏幕导航回来，然后他们的反应不能更新状态。下面是示例代码。在每次状态更新之前写这一行。

if(!isScreenMounted.current) return;

这里是完整的代码

import React , {useRef} from 'react'
import { Text,StatusBar,SafeAreaView,ScrollView, StyleSheet } from 'react-native'
import BASEURL from '../constants/BaseURL';
const SearchScreen = () => {
    const isScreenMounted = useRef(true)
    useEffect(() => {
        return () =>  isScreenMounted.current = false
    },[])

    const ConvertFileSubmit = () => {
        if(!isScreenMounted.current) return;
         setUpLoading(true)
 
         var formdata = new FormData();
         var file = {
             uri: `file://${route.params.selectedfiles[0].uri}`,
             type:`${route.params.selectedfiles[0].minetype}`,
             name:`${route.params.selectedfiles[0].displayname}`,
         };
         
         formdata.append("file",file);
         
         fetch(`${BASEURL}/UploadFile`, {
             method: 'POST',
             body: formdata,
             redirect: 'manual'
         }).then(response => response.json())
         .then(result => {
             if(!isScreenMounted.current) return;
             setUpLoading(false)    
         }).catch(error => {
             console.log('error', error)
         });
     }

    return(
    <>
        <StatusBar barStyle="dark-content" />
        <SafeAreaView>
            <ScrollView
            contentInsetAdjustmentBehavior="automatic"
            style={styles.scrollView}>
               <Text>Search Screen</Text>
            </ScrollView>
        </SafeAreaView>
    </>
    )
}

export default SearchScreen;


const styles = StyleSheet.create({
    scrollView: {
        backgroundColor:"red",
    },
    container:{
        flex:1,
        justifyContent:"center",
        alignItems:"center"
    }
})
2021-07-26 07:54:24

如果上述解决方案不工作，试试这个，它为我工作:

componentWillUnmount() {
    // fix Warning: Can't perform a React state update on an unmounted component
    this.setState = (state,callback)=>{
        return;
    };
}
2020-04-06 08:39:40

为jsx组件添加一个引用，然后检查它是否存在

function Book() {
  const ref = useRef();

  useEffect(() => {
    asyncOperation().then(data => {
      if (ref.current) setState(data);
    })
  });

  return <div ref={ref}>content</div>
}
2021-09-10 11:23:49

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