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[英]what is the difference between using useEffect inside a custom hook and a component
[英]Error using custom hook inside a useEffect
let { photos, isQuering, empty, error } = useFetch(brand, isOld);
useEffect(() => {
if (isOld) {
const { photos: photosTest } = useFetch(brand, isOld);
photos = photosTest;
}
}, [isOld]);
useFetch 是我有的自定义钩子,我想在 isOld 状态为真时带上旧照片,上面的代码 useEffect 正常调用并加载照片,但我遇到了 useFetch 没有在 body 内部被调用的错误一个函数组件,出现以下错误“无效的钩子调用。只能在函数组件的主体内部调用钩子。这可能是由于以下原因之一:”,也就是说,我做错了什么不能看! 如果您能帮助我,我将不胜感激!
因为丹科而编辑! 钩子!
import { useEffect, useState, useContext } from 'react';
import { useScrollPagination } from './flow-manager';
import { db } from '../../Firebase';
import { userContext } from '../appContext';
export default function fetch(brand, isOld) {
const {
userData: { uid },
} = useContext(userContext);
const [photos, setPhotos] = useState([]);
const [lastDoc, setLastDoc] = useState(undefined);
const [isQuering, setIsQuering] = useState(false);
const [empty, setEmpty] = useState(false);
const [error, setError] = useState();
const [finished, setFinished] = useState(false);
const shouldFetchMore = useScrollPagination();
const [shouldKeepFecthing, setShouldKeepFetching] = useState(false);
useEffect(() => {
if (isQuering || finished) return;
if (!lastDoc || shouldFetchMore || shouldKeepFecthing) {
setIsQuering(true);
let query = !isOld
? db
.collection('catalog-images')
.where('brandName', '==', brand)
.orderBy('timestamp', 'desc')
.endBefore(new Date().setDate(new Date().getDate() - 40))
.limit(20)
: db
.collection('catalog-images')
.where('brandName', '==', brand)
.where('photoPeriod', '==', 'Antiga')
.limit(20);
if (lastDoc) query = query.startAfter(lastDoc);
query
.get()
.then(snap => {
const newPhotos = [];
let valid = 0;
snap.forEach(doc => {
const { url, pricetag, timestamp } = doc.data();
if (!uid && pricetag === 'Sim') return;
brand && newPhotos.push({ url, timestamp });
valid += 1;
});
setPhotos(oldPhotos => [...oldPhotos, ...newPhotos]);
setShouldKeepFetching(valid < 10);
setEmpty(snap.empty);
setLastDoc(snap.docs[snap.docs.length - 1]);
setFinished(snap.docs.length < 20);
setIsQuering(false);
})
.catch(setError);
}
}, [!!lastDoc, shouldFetchMore, shouldKeepFecthing, isQuering]);
return { photos, isQuering, empty, error, fetch };
}
最后更新:在这里,我调用钩子的地方:
let {
photos,
isQuering,
empty,
error,
useFetch: refetch,
} = useFetch(brand, isOld);
useEffect(() => {
if (isOld) {
let { photos: photosTest } = refetch(brand, isOld);
photos = photosTest;
setIsOld(false);
}
}, [isOld]);
Aaaand,钩子:
import { useEffect, useState, useContext } from 'react';
import { useScrollPagination } from './flow-manager';
import { db } from '../../Firebase';
import { userContext } from '../appContext';
export default function useFetch(brand, isOld) {
const {
userData: { uid },
} = useContext(userContext);
const [photos, setPhotos] = useState([]);
const [lastDoc, setLastDoc] = useState(undefined);
const [isQuering, setIsQuering] = useState(false);
const [empty, setEmpty] = useState(false);
const [error, setError] = useState();
const [finished, setFinished] = useState(false);
const shouldFetchMore = useScrollPagination();
const [shouldKeepFecthing, setShouldKeepFetching] = useState(false);
useEffect(() => {
if (isQuering || finished) return;
if (!lastDoc || shouldFetchMore || shouldKeepFecthing) {
setIsQuering(true);
let query = !isOld
? db
.collection('catalog-images')
.where('brandName', '==', brand)
.orderBy('timestamp', 'desc')
.endBefore(new Date().setDate(new Date().getDate() - 40))
.limit(20)
: db
.collection('catalog-images')
.where('brandName', '==', brand)
.where('photoPeriod', '==', 'Antiga')
.limit(20);
if (lastDoc) query = query.startAfter(lastDoc);
query
.get()
.then(snap => {
const newPhotos = [];
let valid = 0;
snap.forEach(doc => {
const { url, pricetag, timestamp } = doc.data();
if (!uid && pricetag === 'Sim') return;
brand && newPhotos.push({ url, timestamp });
valid += 1;
});
setPhotos(oldPhotos => [...oldPhotos, ...newPhotos]);
setShouldKeepFetching(valid < 10);
setEmpty(snap.empty);
setLastDoc(snap.docs[snap.docs.length - 1]);
setFinished(snap.docs.length < 20);
setIsQuering(false);
})
.catch(setError);
}
}, [!!lastDoc, shouldFetchMore, shouldKeepFecthing, isQuering]);
return { photos, isQuering, empty, error, useFetch };
}
我建议别的:
useFetch
以便它具有refetch
函数结束将其添加到返回的对象。const { photos, isQuering, empty, error, refetch } = useFetch(brand);
useEffect(() => {
if(isOld) {
refetch();
setIsOld(false)
}
}, [isOld]);
您必须重命名您的 custon hook 以开始use
。 否则,react 无法将其与其他功能区分开来。 因此,与其将其命名为fetch
, useFetch
将其重命名为useFetch
。
问题是,你不能从另一个钩子调用一个钩子。 钩子只能从组件主体(顶级)调用。 您的代码在几个层面上毫无意义:
let { photos, isQuering, empty, error } = useFetch(brand, isOld);
useEffect(() => {
if (isOld) {
const { photos: photosTest } = useFetch(brand, isOld); // can't call a hook here
photos = photosTest; // can't mutate component-level variables
}
}, [isOld]);
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