使用React的useState钩子时,正确的方式来键入可空状态

Question

我无法弄清楚如何输入useState函数,因为它返回一个元组.本质上,我必须提供ie的null初始值,因为email我假设我不能在这里使用空字符串.

然后我有setEmail功能来更新这个状态值,它将电子邮件作为字符串.

理想情况下,我想输入我的,useState所以它希望电子邮件是字符串或null,如果可能的话.目前它只是继承它null

import * as React from "react";

const { useState } = React;

function Example() {
  const [state, setState] = useState({ email: null, password: null });

  function setEmail(email: string) {
    setState(prevState => ({ ...prevState, email }))
  }

  return <p>{state.email}</p>
}

setEmail函数返回以下错误,因为string函数参数不是null指定的有效类型useState()

[ts]
Argument of type '(prevState: { email: null; password: null; }) => { email: string; password: null; }' is not assignable to parameter of type 'SetStateAction<{ email: null; password: null; }>'.
  Type '(prevState: { email: null; password: null; }) => { email: string; password: null; }' is not assignable to type '(prevState: { email: null; password: null; }) => { email: null; password: null; }'.
    Type '{ email: string; password: null; }' is not assignable to type '{ email: null; password: null; }'.
      Types of property 'email' are incompatible.
        Type 'string' is not assignable to type 'null'. [2345]
(parameter) prevState: {
    email: null;
    password: null;
}

Answer 1

这已经在几个地方得到解决：

https://dev.to/busypeoples/notes-on-typescript-react-hooks-28j2

https://codewithstyle.info/Using-React-useState-hook-with-TypeScript/

TLDR：当初始状态为空时，将类型参数传递给 setState

例如：

const [email, setEmail] = useState<string>();

Answer 2

你可以尝试一下,告诉我它是否有效吗？

const { useState } = React;

function Example() {
  const [state, setState] = useState<{email: null | string, password: null | string}>({ email: null, password: null });

  function setEmail(email: string) {
    setState(prevState => ({ ...prevState, email }))
  }

  return <p>{state.email}</p>
}