[英]React Can't perform a React state update on an unmounted component error
[英]React useState causing “Can't perform a React state update on an unmounted component..” error
我是 React/Node 的新手,正在从事一个学习项目。 这是一个将用户(自由职业者)与非营利公司联系起来的平台。 当用户登录时,他们可以转到 UserConnections 页面以查看他们连接的所有公司。
这工作正常,但我也收到警告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 a useEffect cleanup function.
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 a useEffect cleanup function.
此外,当我访问此组件时,命令行开始以极快的速度无休止地吐出连接消息。
我认为问题来自 UserConnections 组件中使用的这个useEffect
。 这段代码写起来很痛苦,需要这里多人的帮助才能写出来。 我很犹豫要不要碰它。
useEffect(() => {
const comps = connections.map((c) => VolunteerApi.getCurrentCompany(c));
Promise.all(comps).then((comps => setCompanies(comps)));
}
}, [connections]);
我试着像这样重写它:
useEffect(() => {
let isMounted = true;
const comps = connections.map((c) => VolunteerApi.getCurrentCompany(c));
if (isMounted) {
Promise.all(comps).then((comps => setCompanies(comps)));
}
return () => { isMounted = false };
}, [connections]);
但这根本没有改变任何事情。
如何更改此代码以避免内存泄漏而不影响此功能的预期用途? 下面是这个组件的代码。 感谢您的任何帮助。
用户连接
function UserConnections() {
const { currentUser, connectionHandles } = useContext(UserContext);
const connections = currentUser.connections.concat(connectionHandles);
const [companies, setCompanies] = useState([]);
useEffect(() => {
const comps = connections.map((c) => VolunteerApi.getCurrentCompany(c));
Promise.all(comps).then((comps => setCompanies(comps)));
}, [connections]);
if (!companies || companies.length == 0) {
return (
<div>
<p>You have no connections</p>
</div>
)
} else {
return (
<div>
{companies && companies.map(c => (
<CompanyCard
key={c.companyHandle}
companyHandle={c.companyHandle}
companyName={c.companyName}
country={c.country}
numEmployees={c.numEmployees}
shortDescription={c.shortDescription}
/>
))}
</div>
);
}
};
您在重写时几乎正确( isMounted
!) - isMounted
检查需要进入then
。
代替:
if (isMounted) {
Promise.all(comps).then((comps => setCompanies(comps)));
}
你这样写:
Promise.all(comps).then(comps => isMounted && setCompanies(comps));
这也只是一个警告。 你应该修复它,是的,但这不是疯狂的关键。
编辑:
无限循环问题:
const connections = currentUser.connections.concat(connectionHandles);
每次重新渲染组件(调用setCompanies
)时,连接useEffect
发生变化,因此useEffect
引用会发生变化。 修复它的方法是使用connectionHandles
和currentUser
作为效果的依赖项,并在效果内部移动connections
,例如:
function UserConnections() {
const { currentUser, connectionHandles } = useContext(UserContext);
const [companies, setCompanies] = useState([]);
useEffect(() => {
let isMounted = true;
// move connections inside the effect
const connections = currentUser.connections.concat(connectionHandles);
const comps = connections.map((c) => VolunteerApi.getCurrentCompany(c));
Promise.all(comps).then((comps => isMounted && setCompanies(comps)));
return () => { isMounted = false };
}, [currentUser,connectionHandlers]);
...
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