为什么我不能从当前的 state 中获取一个值并在我的 useState 挂钩中使用它？

Question

目前，登录用户的 object 设置为当前 state，从下面的 doe 中您可以看到我是从 authContext 引入的。 我正在尝试获取 user.firstName 值并将其设置为 useState 挂钩内的作者。 当我在我的应用程序中运行它时，我查看存储日志 object 但作者值为空白的数据库。 我对编码很陌生，所以任何建议都将不胜感激！

import React, { useState, useContext } from "react";
import M from "materialize-css/dist/js/materialize.min.js";
import LogContext from "../context/logs/logContext";
import AuthContext from "../context/auth/authContext";

const AddLogModal = () => {
  const logContext = useContext(LogContext);
  const authContext = useContext(AuthContext);

  const { user } = authContext;

  const { addLog } = logContext;

  const [log, setLog] = useState({
    title: "",
    description: "",
    attention: "",
    author: user.firstName,
    date: new Date(),
  });

  const { title, description, attention, author } = log;

  const onChange = (e) => setLog({ ...log, [e.target.name]: e.target.value });

  const onSubmit = (e) => {
    e.preventDefault();
    if (title === "" || description === "" || attention === "") {
      M.toast({ html: "Please enter a title and description.." });
    } else {
      setLog({ ...log, [e.target.name]: e.target.value });
    }

    addLog(log);

    setLog({
      title: "",
      description: "",
      attention: "",
      author: user.firstName,
    });
  };

  return (
    <form id="add-log-modal" className="modal" style={modalStyle}>
      <div className="modal-content">
        <h4>Open New Issue</h4>
        <div className="row">
          <div className="input-field">
            <input type="text" name="title" value={title} onChange={onChange} />
            <label htmlFor="message" className="active">
              Log Title
            </label>
          </div>
        </div>
        <div className="input-field">
          <input
            type="text"
            name="description"
            value={description}
            onChange={onChange}
          />
          <label htmlFor="message" className="active">
            Log Description
          </label>
        </div>
        <div className="input-field">
          <input type="text" name="author" value={author} onChange={onChange} />
          <label htmlFor="message" className="active">
            Created By:
          </label>
        </div>
        <div className="row">
          <div className="input-field">
            <p>
              <label>
                <input
                  type="radio"
                  name="attention"
                  checked={attention === "Needs Attention"}
                  value="Needs Attention"
                  onChange={onChange}
                />
                <span>Needs Attention</span>
              </label>
            </p>
            <p>
              <label>
                <input
                  type="radio"
                  name="attention"
                  checked={attention === "Issue Resolved"}
                  value="Issue Resolved"
                  onChange={onChange}
                />
                <span>Issue Resolved</span>
              </label>
            </p>
          </div>
        </div>
      </div>
      <div className="modal-footer">
        <a
          href="#!"
          onClick={onSubmit}
          className="modal-close waves-effect waves-light blue btn"
        >
          Enter
        </a>
      </div>
    </form>
  );
};

const modalStyle = {
  width: "75%",
  height: "75%",
};

export default AddLogModal;

授权上下文

import React, { useReducer } from "react";
import axios from "axios";
import AuthContext from "./authContext";
import setAuthToken from "../setAuthToken";
import authReducer from "./authReducer";
import {
  REGISTER_SUCCESS,
  REGISTER_FAIL,
  LOGIN_FAIL,
  LOGIN_SUCCESS,
  LOGOUT,
  USER_LOADED,
  AUTH_ERROR,
  CLEAR_ERRORS,
} from "../Types";

const AuthState = (props) => {
  const initialState = {
    token: localStorage.getItem("token"),
    isAuthenticated: false,
    loading: false,
    user: {},
    error: null,
  };

  const [state, dispatch] = useReducer(authReducer, initialState);

  // Load User
  const loadUser = async () => {
    if (localStorage.token) {
      setAuthToken(localStorage.token);
    }
    try {
      const res = await axios.get("/api/auth");

      dispatch({ type: USER_LOADED, payload: res.data });
    } catch (err) {
      dispatch({ type: AUTH_ERROR });
    }
  };

  // Register User
  const register = async (formData) => {
    const config = {
      headers: {
        "Content-type": "application/json",
      },
    };

    try {
      const res = await axios.post("/api/users", formData, config);

      dispatch({
        type: REGISTER_SUCCESS,
        payload: res.data,
      });

      loadUser();
    } catch (err) {
      dispatch({
        type: REGISTER_FAIL,
        payload: err.response.data.msg,
      });
    }
  };
  // Login User
  const login = async (formData) => {
    const config = {
      headers: {
        "Content-type": "application/json",
      },
    };

    try {
      const res = await axios.post("/api/auth", formData, config);

      dispatch({
        type: LOGIN_SUCCESS,
        payload: res.data,
      });

      loadUser();
    } catch (err) {
      dispatch({
        type: LOGIN_FAIL,
        payload: err.response.data.msg,
      });
    }
  };
  // Logout
  const logout = () => {
    dispatch({
      type: LOGOUT,
    });
  };
  // Clear Errors
  const clearErrors = () => {
    dispatch({
      type: CLEAR_ERRORS,
    });
  };

  return (
    <AuthContext.Provider
      value={{
        token: state.token,
        isAuthenticated: state.isAuthenticated,
        loading: state.loading,
        user: state.user,
        error: state.error,
        register,
        login,
        clearErrors,
        loadUser,
        logout,
      }}
    >
      {props.children}
    </AuthContext.Provider>
  );
};

export default AuthState;

Answer 1

反应文档：

如果使用以前的 state 计算新的 state，则可以将 function 传递给 setState。 function 将接收先前的值，并返回更新的值。 下面是一个计数器组件的示例，它同时使用了 setState 的 forms

反应示例：

<button onClick={() => setCount(prevCount => prevCount - 1)}>-</button>