reactjs - useSelector 常量在发送后不更新

Question

这是一个Codesandbox .

getIDs() 更新 cells，然后 initializeCells() 需要它。但是，此更改不会在调度操作后反射(reflect)出来。尽管如此，我还是可以在 Redux dev tools 上看到该操作已完成并且 cells 的值已相应更改。 gameStart() 通过 props 传递给子组件 cells，并通过 useEffect() Hook 调用。我需要传递一个空数组作为此 Hook 的第二个参数，否则它将永远运行，因为每次调用时状态都会更新。问题是在首次运行 getIDs() 之后，新状态不适用于以下函数。似乎是在 gameStart() 完全完成并再次调用时。我需要在 getIDs() 完成后立即更新 initializeCells() 需要的状态。

细胞.js

import React, { useEffect } from "react";
import { useSelector } from "react-redux";

import Cell from "./Container/Container/Cell";

const Cells = props => {
  const board = useSelector(state => state.board);

  useEffect(() => {
    props.gameStart();
  }, []);

  return (
    <div id="cells">
      {board.map(cell => {
        return (
          <Cell
            id={cell.id.substring(1)}
            key={cell.id.substring(1)}
            className="cell"
          />
        );
      })}
    </div>
  );
};

export default Cells;

app.js

import React, { useEffect } from "react";
import { useSelector, useDispatch } from "react-redux";

import {
  setCells,
  setBoard
} from "../../redux/actions/index";

const Game = () => {
  const dispatch = useDispatch();

  const cells = useSelector(state => state.cells);
  const board = useSelector(state => state.board);
  const boardSize = useSelector(state => state.boardSize);

  async function gameStart() {
    await getIDs();
    console.log(cells); // []
    await initializeCells();
    await assignSnake();
    await placeFood();
    await paintCells();
  }

  function getIDs() {
    let cellID = "";
    let collection = [];

    for (let i = 1; i <= boardSize.rows; i++) {
      for (let j = 1; j <= boardSize.columns; j++) {
        cellID = `#cell-${i}-${j}`;

        collection.push(cellID);
      }
    }
    dispatch(setCells(collection));
    console.log(cells); // []
  }

  function initializeCells() {
    console.log(cells); // []
    const board = [];
    // for loop never runs because cells is empty
    for (let i = 0; i < cells.length; i++) {
      board.push(cell(cells[i]));
    }
    dispatch(setBoard(board));
    console.log("Board: ", board); // []
  }

  function cell(id) {
    return {
      id: id,
      row: id.match("-(.*)-")[1],
      column: id.substr(id.lastIndexOf("-") + 1),
      hasFood: false,
      hasSnake: false
    };
  }

  return (
  ...
  )
}

export default Game;

reducers/index.js

import {
  SET_CELLS,
  SET_BOARD
} from "../constants/action-types";

const initialState = {
  board: [],
  cells: [],
  boardSize: {
    rows: 25,
    columns: 40
  }
};

const rootReducer = (state = initialState, action) => {
  switch (action.type) {
    case SET_CELLS:
      return Object.assign({}, state, {
        cells: action.payload
      });

    case SET_BOARD:
      return Object.assign({}, state, {
        board: action.payload
      });

    default:
      return state;
  }
};

actions/index.js

import {
  SET_CELLS,
  SET_BOARD
} from "../constants/action-types";

export const setCells = payload => {
  return { type: SET_CELLS, payload };
};

export const setBoard = payload => {
  return { type: SET_BOARD, payload };
};

constants/action-types.js

export const SET_CELLS = "SET_CELLS";
export const SET_BOARD = "SET_BOARD";

Answer 1

在调度一些 Action 后，更新的商店将仅在下一次渲染时提供。这对于带有钩子(Hook)的函数和带有 connect HOC 的类都是一样的。

您需要更改您的代码，而不是期望立即更改。我很难理解你在这里的意图，你可以从渲染它来的东西开始，然后用行动分派(dispatch)和忘记的方法。它应该有效。

如果没有，制作最小样本(只有相关的钩子(Hook)+数据是如何呈现的)并描述你想要得到什么(而不是“如何”)