示例
在我的场景中,我有一个带有过滤器的侧栏。每个过滤器都是由一个钩子创建的:
list
除其他外,自定义钩子还返回当前选择的值,const filters = {
customerNoFilter: useFilterForMultiCreatable(),
dateOfOrderFilter: useFilterForDate(),
requestedDevliveryDateFilter: useFilterForDate(),
deliveryCountryFilter: useFilterForCodeStable()
//.... these custom hooks are reused for like 10 more filters
}
和诸如reset()
,onChange
之类的处理程序。 (因此,隐藏在自定义钩子中的不只是简单的onRemove
,还请记住这一点)
useState
函数基本上是这样的:
我还实现了一个清除所有过滤器的函数,该函数正在为每个过滤器调用reset()
函数:
reset()
const clearFilters = () => {
const filterValues = Object.values(filters);
for (const filter of filterValues) {
filter.reset();
}
};
函数在每个过滤器中触发状态更新(当然是异步的)以重置所有选定的过滤器。
reset()
重置后立即,我想用重置/更新后的值做事,而不使用状态更新前的值做事,例如使用重置的过滤器调用API:
// setSelected is the setter comming from the return value of a useState statement
const reset = () => setSelected(initialSelected);
在这种情况下,使用旧值调用API(在clearFilters();
callAPI();
中进行更新之前)
那么我如何等待所有过滤器完成更新后的状态呢?我的代码结构不好吗?我在监督什么吗?
对于单状态更新,我可以简单地使用reset()
,但是在等待多个状态更新时,这确实很麻烦。
请不要以身作则,因为我在完全不同的情况下经常会遇到这个问题。
答案 0 :(得分:0)
因此,我通过实现名为useStateWithPromise
的自定义钩子提出了一个解决方案:
import { SetStateAction, useEffect, useRef, useState } from "react";
export const useStateWithPromise = <T>(initialState: T):
[T, (stateAction: SetStateAction<T>) => Promise<T>] => {
const [state, setState] = useState(initialState);
const readyPromiseResolverRef = useRef<((currentState: T) => void) | null>(
null
);
useEffect(() => {
if (readyPromiseResolverRef.current) {
readyPromiseResolverRef.current(state);
readyPromiseResolverRef.current = null;
}
/**
* The ref dependency here is mandatory! Why?
* Because the useEffect would never be called if the new state value
* would be the same as the current one, thus the promise would never be resolved
*/
}, [readyPromiseResolverRef.current, state]);
const handleSetState = (stateAction: SetStateAction<T>) => {
setState(stateAction);
return new Promise(resolve => {
readyPromiseResolverRef.current = resolve;
}) as Promise<T>;
};
return [state, handleSetState];
};
此挂钩将允许await
状态更新:
const [selected, setSelected] = useStateWithPromise<MyFilterType>();
// setSelected will now return a promise
const reset = () => setSelected(undefined);
const clearFilters = () => {
const promises = Object.values(filters).map(
filter => filter.reset()
);
return Promise.all(promises);
};
await clearFilters();
callAPI();
是的,我可以等待状态更新!不幸的是,如果callAPI()
依赖于更新的状态值,这不是全部。
const [filtersToApply, setFiltersToApply] = useState(/* ... */);
//...
const callAPI = () => {
// filtersToApply will still contain old state here, although clearFilters() was "awaited"
endpoint.getItems(filtersToApply);
}
之所以会这样,是因为callAPI
之后执行的await clearFilters();
函数未重新呈现,因此它指向旧状态。但是有一个窍门,需要额外的useRef
才能在清除过滤器后强制重新渲染:
useEffect(() => {
if (filtersCleared) {
callAPI();
setFiltersCleared(false);
}
// eslint-disable-next-line
}, [filtersCleared]);
//...
const handleClearFiltersClick = async () => {
await orderFiltersContext.clearFilters();
setFiltersCleared(true);
};
这将确保在执行callAPI
之前将其重新呈现。
就是这样!恕我直言,有点混乱,但它可以工作。