reactjs - 在 useEffect 中使用 useState 值而不使状态更新 useEffect

Question

我正在开发一个基于对象键管理字符串数组的函数。假设它看起来像这样:

import React, { useState, useEffect } from "react";
import FieldContext from "../contexts/FieldContext";
import io from "socket.io-client";

const [socket, setSocket] = useState(null);
// the `data` array gets changed every second due to a WebSocket, in case that's important
const [data, setData] = useState({ foo: [], bar: [] });
const [connections, setConnections] = useState(["conn1", "conn2"]);

const { checkedFields } = useContext(FieldContext); // ["foo", "moo"];

useEffect(() => {
  setConnections(prevConnections => {
    // The code below does the following: 
    // Loop through the temporary connections (which is a copy of checkedFields)
    // A. if `tempConn` is a key in the `data` object, push the name with `update_` prefix to the `_conns` array
    // B. If not, just push it without a prefix to the `_conns` array
    // Since the `checkedFields` array is ["foo", "moo"], the first element will get the prefix,
    // the other won't and will just get pushed.
    let _tempConns = [...checkedFields];
    let _conns = [];
    _tempConns.forEach(tempConn => {
      if (data[tempConn] !== undefined) _conns.push(`update_${tempConn}`);
      else _conns.push(tempConn);
    });
    return _conns;
  });
}, [checkedFields]);

// the websocket hook
useEffect(() => {
  const _socket = io(WS_URI);
  _socket.on("info", data => {
    // some magic happens here to add to the `data` object which is not important for this question
  });
  setSocket(_socket);
}, [])

使用此 Hook 时收到以下警告:React Hook useEffect has a missing dependency: 'data'. Either include it or remove the dependency array .我明白，但如果我包括 data在依赖数组中，我得到了大量不必要的更新。我该如何防止这种情况发生？ (请不要使用// eslint-disable-next-line)

Answer 1

您不仅缺少data来自 useEffect 的依赖数组钩，但你也错过了setConnections()依赖数组中的函数。
您可以使用 useReducer将状态更新逻辑移出 useEffect 的钩子(Hook)钩。

const initialState = {
   data: { foo: [], bar: [] },
   connections: ["conn1", "conn2"]
} 

const reducerFunc = (state, action) => {
   switch(action.type) {
       case 'UPDATE_CONNECTIONS':
          let _tempConns = [...action.checkedFields];
          let _conns = [];
          _tempConns.forEach(tempConn => {
              if (state.data[tempConn] !== undefined) _conns.push(`update_${tempConn}`);
              else _conns.push(tempConn);
          });
          return { ...state, connections: _conns };
        default: 
          return state;
   }
};

const [myState, dispatch] = useReducer(reducerFunc, initialState);

const { checkedFields } = useContext(FieldContext); // ["foo", "moo"];

useEffect(() => {
    dispatch({ type: 'UPDATE_CONNECTIONS', payload: checkedFields });
}, [checkedFields]);

由于 React 确保 dispatch函数不会改变，你可以从 useEffect 中省略它hook 的依赖数组。
详细使用方法useReducer Hook ，请参阅以下链接:

useReducer Hook - React Hooks Cheatsheet

useReducer Hook - React docs