React Hooks useState Array 为空，在组件中呈现状态

Question

I have a situation where i can successfully dispatch my states with reducers and i can render it in my component

Here the relevant code

in my action/index.js

export const receivedLeaguesList = json => ({
  type: RECEIVE_LEAGUES_LIST,
  json: json
});

export function fetchLeaguesList() {
  return function(dispatch) {
    dispatch(requestLeaguesList());
      return axios
        .get("https://www.api-football.com/demo/v2/leagues/")
        .then(res => {
          let leagues = res.data.api.leagues;
          dispatch(receivedLeaguesList(leagues));
        })
        .catch(e => {
          console.log(e);
        });
    }
}

my reducers/index.js

import { REQUEST_LEAGUES_LIST, RECEIVE_LEAGUES_LIST } from "../actions";

const initialState = {
  leaguesList: [],
  isLeagueListLoading: false
};

const reducer = (state = initialState, action) => {
  switch (action.type) {
    case REQUEST_LEAGUES_LIST:
      return { ...state, isLeagueListLoading: true };
    case RECEIVE_LEAGUES_LIST:
      return { ...state, leaguesList: action.json, isLeagueListLoading: false };
    default:
      return state;
  }
};

in my component component/Leagues.js

let Leagues = ({ leaguesList, loading, getList }) => {
  useEffect(() => {
    getList();
  }, [getList]);


  const [itemsLeagues] = useState([leaguesList]);

  console.log("league list", itemsLeagues);

const mapDispatchToProps = {
  getList: fetchLeaguesList
};

I have reproduced the demo here => https://codesandbox.io/s/select-demo-71u7h ?

I can render my leaguesList states in my component doing the map, but why when

  const [itemsLeagues] = useState([leaguesList]);

  console.log("league list", itemsLeagues); 

returns an empty array?

See the image

Answer 1

You're setting useState's init value wrong:

 const [itemsLeagues] = useState(leaguesList);

instead of

 const [itemsLeagues] = useState([leaguesList]);

The return value of useState isn't the value itself, but the array of value and mutator:

const [value, setValue] = useState([42, 43])
// here's value equals [42, 43]

So if you were trying to destructure the wrapping array you passed to useState(), you should use it like this (though you don't need it):

const [[itemsLeagues]] = useState([leaguesList]);