React Typescript：类型参数不可分配给类型参数

Question

It is a React component to create a Check Box Button, I am having this error in setRSelected(1),setRSelected(2)...

  const [cSelected, setCSelected] = useState([]);
  const [rSelected, setRSelected] = useState();

  const onCheckboxBtnClick = (selected: never) => {
    const index = cSelected.indexOf(selected);
    if (index < 0) {
      cSelected.push(selected);
    } else {
      cSelected.splice(index, 1);
    }
    setCSelected([...cSelected]);
  }
  return (
    <div>
      <h5>Radio Buttons</h5>
      <ButtonGroup>
        <Button color="primary" onClick={() => setRSelected(1)} active={rSelected === 1}>One</Button>
        <Button color="primary" onClick={() => setRSelected(2)} active={rSelected === 2}>Two</Button>
        <Button color="primary" onClick={() => setRSelected(3)} active={rSelected === 3}>Three</Button>
      </ButtonGroup>
      <p>Selected: {rSelected}</p>
    </div>
  );
} 

and I get this error: Argument of type '1' is not assignable to parameter of type 'SetStateAction<undefined>'.

How can I fix this

Answer 1

You should declare type when use useState like this:

const [rSelected, setRSelected] = useState<number | undefined>();