Question

导航到其他状态后，我无法获得更新状态。我想使用在reducer中初始化并通过操作更新的dataState。在屏幕1上调度后，我使用了此状态，但是当我导航到另一个屏幕时，它返回未定义的状态。

store.js

import { createStore, applyMiddleware } from 'redux';
import thunk from 'redux-thunk';

import reducers from './reducers.js';


export default createStore(reducers, applyMiddleware(thunk));

action.js

export const DATA_AVAILABLE = 'DATA_AVAILABLE';

export const addData = (data) => ({
    type: DATA_AVAILABLE,
    data
});

reducers.js

import { combineReducers } from 'redux';

import { DATA_AVAILABLE } from "./actions" 

let dataState = { data: [] };

const dataReducer = (state = dataState, action) => {
    switch (action.type) {
        case DATA_AVAILABLE:
            return {...state, data: action.data};
        default:
            return state;
    }
};


const rootReducer = combineReducers({
    dataReducer
})

export default rootReducer;

HomeScreen.js的用法

const dataReducer = useSelector(state => state.dataReducer);
const { data } = dataReducer;

useEffect(() => getData(), []);

const getData = () => {
    setIsFetching(true);
    let url =
      "https://my-json-server.typicode.com/mesandigital/demo/instructions";
    axios
      .get(url)
      .then(res => res.data)
      .then(data => dispatch(addData(data)))
      .catch(error => alert(error.message))
      .finally(() => setIsFetching(false));
  };

可以使用数据常量访问获取的数据。因此，这意味着dataState的状态在获取后会更新。但是，当我导航到其他屏幕并尝试访问dataState时，它将返回undefined。我正在该屏幕上访问商店状态：

const dataReducer = useSelector(state => state.dataReducer);
const { data } = dataReducer;

数据常量返回未定义。我想念什么吗？

Answer 1

好的，我在代码中发现了问题。我在useSelector之后设置了恒定值。我直接调用useSelector常量，它起作用了。问题是当我调用它时没有设置另一个常量。还是谢谢你

导航后未定义React Native Redux useSelector

1 个答案: