具有动态数组长度的 React 钩子

Question

I have the following dummy example:

function App({size}) {
  const [values, setValues] = React.useState(Array(size).fill(''));
  function onChange(index, event) {
    console.log('setting index: ', index)
    console.log('to value: ', event.target.value);
    values[index] = event.target.value;
    setValues(values);
  }

  console.log('values are');
  console.log(values);

  const inputs = Array(size).fill().map((_, index) => (
    <input
      key={`input-${index}`}
      value={values[index]}
      onChange={e => onChange(index, e)}
    />
  ));

  return (
    <React.Fragment>
      {inputs}
    </React.Fragment>
  )
}

ReactDOM.render(
  <App size={3} />,
  document.getElementById('container')
);

I expect to be able to pass size to App and dynamically get that many inputs.

When I run this and type in the inputs, I see

values are
["", "", "", ""]
setting index: 3
to value: s
setting index: 1
to value: e
setting index: 0
to value: f

Looks like my component is not re-rendered. Why is that?

Answer 1

Your issue is most likely that you're trying to directly mutate state. In your onChange function, you should instead make sure not to try to mutate it.

function onChange(index, event) {
  const newValues = values.map((value, i) => {
    return i === index ? event.target.value : value;
  });
  setValues(newValues);
}

Answer 2

As @Nick mentioned, the problem was that I was directly mutating the state itself. I ended up using the following approach (instead of Nick's approach which does work):

function onChange(index, event) {
  const newValues = [...values];
  newValues[index] = event.target.value;
  setValues(newValues);
}