[英]Setting the initial value of a useState hook before useState is executed
因此,我正在嘗試從本地存儲中為 Chrome 擴展加載一些數據。 我需要使用這些數據來設置 useState 掛鈎的初始值。 這是我到目前為止所嘗試的:
const Popup = (): ReactElement => {
// load state from local storage
let overviewIsOpenLS;
useLayoutEffect(() => {
chrome.runtime.sendMessage({ getFromLocalStorage: 'overviewIsOpen' }, response => {
overviewIsOpenLS = response;
});
}, []);
console.log(overviewIsOpenLS); // returns undefined
// trying to use the value of overviewIsOpenLS as the initial value of this useState
const [overviewIsOpen, setOverviewIsOpen] = useState<boolean>(overviewIsOpenLS);
return <>...
}
我兩次/三次檢查了本地存儲中的值,它是正確的。 但是,此時頂部的 useEffect 不起作用,變量仍未定義。 知道如何實現嗎?
我會在父組件中發出異步請求,然后僅在請求完成后有條件地呈現子組件( Popup
):
// parent component
const [overviewIsOpenLS, setOverviewIsOpenLS] = useState();
useLayoutEffect(() => {
chrome.runtime.sendMessage({ getFromLocalStorage: 'overviewIsOpen' }, setOverviewIsOpenLS);
}, []);
return overviewIsOpenLS === undefined ? null : <Popup overviewIsOpenLS={overviewIsOpenLS} />;
// then in Popup:
const [overviewIsOpen, setOverviewIsOpen] = useState<boolean>(props.overviewIsOpenLS);
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