我有下面的useEffect函数,想找一个最好的方法来清理这个组件卸载时的问题。
我想最好是按照 makeCancelable
从React 文件然而,当承诺被取消时,代码仍然会执行。
const makeCancelable = (promise) => {
let hasCanceled_ = false;
const wrappedPromise = new Promise((resolve, reject) => {
promise.then(
val => hasCanceled_ ? reject({isCanceled: true}) : resolve(val),
error => hasCanceled_ ? reject({isCanceled: true}) : reject(error)
);
});
return {
promise: wrappedPromise,
cancel() {
hasCanceled_ = true;
},
};
};
//example useEffect
useEffect(() => {
const getData = async () => {
const collectionRef_1 = await firestore.collection(...)
const collectionRef_2 = await firestore.collection(...)
if (collectionRef_1.exists) {
//update local state
//this still runs!
}
if (collectionRef_2.exists) {
//update local state
//and do does this!
}
}
const getDataPromise = makeCancelable(new Promise(getData))
getDataPromise.promise.then(() => setDataLoaded(true))
return () => getDataPromise.cancel()
}, [dataLoaded, firestore])
我还尝试了 const getDataPromise = makeCancelable(getData)
没有任何运气。代码执行得很好,只是在组件卸载时没有正确清理。
我是否也需要取消这两个 await 函数?
在你的 makeCancelable
函数的值,你只是检查 hasCanceled_
约定之后 意思 getData
已经完全执行了)。)
const makeCancelable = (promise) => {
let hasCanceled_ = false;
const wrappedPromise = new Promise((resolve, reject) => {
// AFTER PROMISE RESOLVES (see following '.then()'!), check if the
// react element has unmount (meaning the cancel function was called).
// If so, just reject it
promise.then(
val => hasCanceled_ ? reject({isCanceled: true}) : resolve(val),
error => hasCanceled_ ? reject({isCanceled: true}) : reject(error)
);
});
return {
promise: wrappedPromise,
cancel() {
hasCanceled_ = true;
},
};
};
相反,在这种情况下,我建议你采用更简单更经典的解决方案,使用 isMounted
变量来创建你想要的逻辑。
useEffect(() => {
let isMounted = true
const getData = async () => {
const collectionRef_1 = await firestore.collection(...)
const collectionRef_2 = await firestore.collection(...)
if (collectionRef_1.exists && isMounted) {
// this should not run if not mounted
}
if (collectionRef_2.exists && isMounted) {
// this should not run if not mounted
}
}
getData().then(() => setDataLoaded(true))
return () => {
isMounted = false
}
}, [dataLoaded, firestore])