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;
这是一个React挂钩的具体解决方案
错误
警告:无法对未挂载的组件执行React状态更新。
解决方案
您可以在useEffect内部声明let isMounted = true,一旦组件被卸载,它将在清理回调中被更改。在状态更新之前,你现在有条件地检查这个变量:
useEffect(() => {
let isMounted = true; // note mutable flag
someAsyncOperation().then(data => {
if (isMounted) setState(data); // add conditional check
})
return () => { isMounted = false }; // cleanup toggles value, if unmounted
}, []); // adjust dependencies to your needs
const Parent = () => {
const [mounted, setMounted] = useState(true);
return (
<div>
Parent:
<button onClick={() => setMounted(!mounted)}>
{mounted ? "Unmount" : "Mount"} Child
</button>
{mounted && <Child />}
<p>
Unmount Child, while it is still loading. It won't set state later on,
so no error is triggered.
</p>
</div>
);
};
const Child = () => {
const [state, setState] = useState("loading (4 sec)...");
useEffect(() => {
let isMounted = true;
fetchData();
return () => {
isMounted = false;
};
// simulate some Web API fetching
function fetchData() {
setTimeout(() => {
// drop "if (isMounted)" to trigger error again
// (take IDE, doesn't work with stack snippet)
if (isMounted) setState("data fetched")
else console.log("aborted setState on unmounted component")
}, 4000);
}
}, []);
return <div>Child: {state}</div>;
};
ReactDOM.render(<Parent />, document.getElementById("root"));
<script src="https://cdnjs.cloudflare.com/ajax/libs/react/16.13.0/umd/react.production.min.js" integrity="sha256-32Gmw5rBDXyMjg/73FgpukoTZdMrxuYW7tj8adbN8z4=" crossorigin="anonymous"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react-dom/16.13.0/umd/react-dom.production.min.js" integrity="sha256-bjQ42ac3EN0GqK40pC9gGi/YixvKyZ24qMP/9HiGW7w=" crossorigin="anonymous"></script>
<div id="root"></div>
<script>var { useReducer, useEffect, useState, useRef } = React</script>
扩展:自定义useAsync钩子
我们可以将所有样板包封装到一个自定义Hook中,当组件卸载或依赖值之前发生更改时,该Hook会自动中止异步函数:
function useAsync(asyncFn, onSuccess) {
useEffect(() => {
let isActive = true;
asyncFn().then(data => {
if (isActive) onSuccess(data);
});
return () => { isActive = false };
}, [asyncFn, onSuccess]);
}
// custom Hook for automatic abortion on unmount or dependency change
// You might add onFailure for promise errors as well.
function useAsync(asyncFn, onSuccess) {
useEffect(() => {
let isActive = true;
asyncFn().then(data => {
if (isActive) onSuccess(data)
else console.log("aborted setState on unmounted component")
});
return () => {
isActive = false;
};
}, [asyncFn, onSuccess]);
}
const Child = () => {
const [state, setState] = useState("loading (4 sec)...");
useAsync(simulateFetchData, setState);
return <div>Child: {state}</div>;
};
const Parent = () => {
const [mounted, setMounted] = useState(true);
return (
<div>
Parent:
<button onClick={() => setMounted(!mounted)}>
{mounted ? "Unmount" : "Mount"} Child
</button>
{mounted && <Child />}
<p>
Unmount Child, while it is still loading. It won't set state later on,
so no error is triggered.
</p>
</div>
);
};
const simulateFetchData = () => new Promise(
resolve => setTimeout(() => resolve("data fetched"), 4000));
ReactDOM.render(<Parent />, document.getElementById("root"));
<script src="https://cdnjs.cloudflare.com/ajax/libs/react/16.13.0/umd/react.production.min.js" integrity="sha256-32Gmw5rBDXyMjg/73FgpukoTZdMrxuYW7tj8adbN8z4=" crossorigin="anonymous"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react-dom/16.13.0/umd/react-dom.production.min.js" integrity="sha256-bjQ42ac3EN0GqK40pC9gGi/YixvKyZ24qMP/9HiGW7w=" crossorigin="anonymous"></script>
<div id="root"></div>
<script>var { useReducer, useEffect, useState, useRef } = React</script>
更多关于效果清理:过度反应:使用效果的完整指南
这是一个React挂钩的具体解决方案
错误
警告:无法对未挂载的组件执行React状态更新。
解决方案
您可以在useEffect内部声明let isMounted = true,一旦组件被卸载,它将在清理回调中被更改。在状态更新之前,你现在有条件地检查这个变量:
useEffect(() => {
let isMounted = true; // note mutable flag
someAsyncOperation().then(data => {
if (isMounted) setState(data); // add conditional check
})
return () => { isMounted = false }; // cleanup toggles value, if unmounted
}, []); // adjust dependencies to your needs
const Parent = () => {
const [mounted, setMounted] = useState(true);
return (
<div>
Parent:
<button onClick={() => setMounted(!mounted)}>
{mounted ? "Unmount" : "Mount"} Child
</button>
{mounted && <Child />}
<p>
Unmount Child, while it is still loading. It won't set state later on,
so no error is triggered.
</p>
</div>
);
};
const Child = () => {
const [state, setState] = useState("loading (4 sec)...");
useEffect(() => {
let isMounted = true;
fetchData();
return () => {
isMounted = false;
};
// simulate some Web API fetching
function fetchData() {
setTimeout(() => {
// drop "if (isMounted)" to trigger error again
// (take IDE, doesn't work with stack snippet)
if (isMounted) setState("data fetched")
else console.log("aborted setState on unmounted component")
}, 4000);
}
}, []);
return <div>Child: {state}</div>;
};
ReactDOM.render(<Parent />, document.getElementById("root"));
<script src="https://cdnjs.cloudflare.com/ajax/libs/react/16.13.0/umd/react.production.min.js" integrity="sha256-32Gmw5rBDXyMjg/73FgpukoTZdMrxuYW7tj8adbN8z4=" crossorigin="anonymous"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react-dom/16.13.0/umd/react-dom.production.min.js" integrity="sha256-bjQ42ac3EN0GqK40pC9gGi/YixvKyZ24qMP/9HiGW7w=" crossorigin="anonymous"></script>
<div id="root"></div>
<script>var { useReducer, useEffect, useState, useRef } = React</script>
扩展:自定义useAsync钩子
我们可以将所有样板包封装到一个自定义Hook中,当组件卸载或依赖值之前发生更改时,该Hook会自动中止异步函数:
function useAsync(asyncFn, onSuccess) {
useEffect(() => {
let isActive = true;
asyncFn().then(data => {
if (isActive) onSuccess(data);
});
return () => { isActive = false };
}, [asyncFn, onSuccess]);
}
// custom Hook for automatic abortion on unmount or dependency change
// You might add onFailure for promise errors as well.
function useAsync(asyncFn, onSuccess) {
useEffect(() => {
let isActive = true;
asyncFn().then(data => {
if (isActive) onSuccess(data)
else console.log("aborted setState on unmounted component")
});
return () => {
isActive = false;
};
}, [asyncFn, onSuccess]);
}
const Child = () => {
const [state, setState] = useState("loading (4 sec)...");
useAsync(simulateFetchData, setState);
return <div>Child: {state}</div>;
};
const Parent = () => {
const [mounted, setMounted] = useState(true);
return (
<div>
Parent:
<button onClick={() => setMounted(!mounted)}>
{mounted ? "Unmount" : "Mount"} Child
</button>
{mounted && <Child />}
<p>
Unmount Child, while it is still loading. It won't set state later on,
so no error is triggered.
</p>
</div>
);
};
const simulateFetchData = () => new Promise(
resolve => setTimeout(() => resolve("data fetched"), 4000));
ReactDOM.render(<Parent />, document.getElementById("root"));
<script src="https://cdnjs.cloudflare.com/ajax/libs/react/16.13.0/umd/react.production.min.js" integrity="sha256-32Gmw5rBDXyMjg/73FgpukoTZdMrxuYW7tj8adbN8z4=" crossorigin="anonymous"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react-dom/16.13.0/umd/react-dom.production.min.js" integrity="sha256-bjQ42ac3EN0GqK40pC9gGi/YixvKyZ24qMP/9HiGW7w=" crossorigin="anonymous"></script>
<div id="root"></div>
<script>var { useReducer, useEffect, useState, useRef } = React</script>
更多关于效果清理:过度反应:使用效果的完整指南