reactjs - React/Recoil - setAtom 新值何时可用？

Question

我正在尝试了解 React Recoil 以及更新后的原子值何时可用，或者如何使新值在应用程序中垂直和水平传播。

例如，如果我有一个名为 userState 的原子，并且我更新了它的一个属性，如 avatar_url，如果我在设置用户。

const [user, setUser] = useRecoilState(userState);

setUser({ avatar_url: imageURL, ...appUser});

console.log(imageURL); // is the actual new URL
console.log(user.avatar_url); // should be new URL but isn't

Answer 1

与Recoil无关，与React有关，更新值可用on the next render因为 setState(Recoil 的基础)是异步的。

setState() does not immediately mutate this.state but creates apending state transition. Accessing this.state after calling thismethod can potentially return the existing value. There is noguarantee of synchronous operation of calls to setState and calls maybe batched for performance gains.

你应该使用 useEffect 来模拟这个行为:

const [user, setUser] = useRecoilState(userState);

setUser({ avatar_url: imageURL, ...appUser});

useEffect(() => {
  console.log(user.avatar_url);
}, [user]);