类型 'unknown' 不可分配给类型 '(prevState: number | undefined) => number |不明确的'

Question

我正在使用 material ui 的 select 组件将 selected 值保存在变量中：

const [ratio, setRatio] = useState<number>();
...
const handleChangeRatio = (e: React.ChangeEvent<{ name?: string | undefined; value: unknown; }>) => {
    //const value = typeof e.target.value === "number" ? e.target.value : "";
    setRatio(e.target.value);
};
...
    <Select
        labelId="demo-simple-select-filled-label"
        id="demo-simple-select-filled"
        value={splittingMethod}
        onChange={(e)=>handleChangeRatio(e)}
    >
        <MenuItem value={0}>
            0
        </MenuItem>
        <MenuItem value={0.1}>0.1</MenuItem>
        <MenuItem value={0.2}>0.2</MenuItem>
    </Select>

但是，我在 handleChange 函数中设置状态时遇到此错误，我该如何解决？

Argument of type 'unknown' is not assignable to parameter of type 'SetStateAction<number | undefined>'.
  Type 'unknown' is not assignable to type '(prevState: number | undefined) => number | undefined'.

Answer 1

React 的 useState<number>() returns 值元组，类型为：ratio: number | undefined、setRatio: SeStateAction<number | undefined>。当您尝试输入 setRatio 类型 unknown 的值时。

最简单的方法是 narrow 类型 unknown 到 number:

const handleChangeRatio = (e: React.ChangeEvent<{ value: unknown }>) => {
    if (typeof e.target.value === 'number') setRatio(e.target.value)
};

或具有更好的运行时安全性：

const handleChangeRatio = (e: React.ChangeEvent<{ value: unknown }>) => {
    const value = Number(e.target.value)
    if (!isNaN(value)) setRatio(value)
};

类型 'unknown' 不可分配给类型 '(prevState: number | undefined) => number |不明确的'

Type 'unknown' is not assignable to type '(prevState: number | undefined) => number | undefined'

javascript

setstate

typescript

reactjs

react-native