Uncaught (in promise) TypeError: dispatch is not a function useContext/useReducer

Question

我是新手。我在一个博客网站上工作，我需要在其中创建一个登录页面。我面临以下错误： TypeError: dispatch 不是函数

以下是我处理提交和请求 API 的代码。我正进入（状态 ...

const { dispatch, isFetching } = useContext(Context);
const handleSubmit = async (e) => {
    e.preventDefault();
    dispatch({ type: "LOGIN_START" });
    try {
      const res = await axios.post("http://localhost:5001/api/auth/login", {
        username: userRef.current.value,
        password: passwordRef.current.value,
      });
      dispatch({ type: "LOGIN_SUCCESS", payload: res.data });
    } catch (err) {
      dispatch({ type: "LOGIN_FAILURE" });
    }
  };

...

以下是我的表单代码：

...

return (
    <div className="login">
      <span className="loginTitle">Login</span>
      <form className="loginForm" onSubmit={(e) => handleSubmit(e)}>
        <label>Username</label>
        <input
          type="text"
          className="loginInput"
          placeholder="Enter your username..."
          ref={userRef}
        />
        <label>Password</label>
        <input
          type="password"
          className="loginInput"
          placeholder="Enter your password..."
          ref={passwordRef}
        />
        <button className="loginButton" type="submit" disabled={isFetching}>
          Login
        </button>
      </form>
      <button className="loginRegisterButton">
        <Link className="link" to="/register">
          Register
        </Link>
      </button>
    </div>
  );

...

以下是上下文提供程序

...

import { createContext, useEffect, useReducer } from "react";
import Reducer from "./Reducer";

const INITIAL_STATE = {
  user: JSON.parse(localStorage.getItem("user")) || null,
  isFetching: false,
  error: false,
};

export const Context = createContext(INITIAL_STATE);

export const ContextProvider = ({ children }) => {
  const [state, dispatch] = useReducer(Reducer, INITIAL_STATE);

  useEffect(() => {
    localStorage.setItem("user", JSON.stringify(state.user));
  }, [state.user]);

  return (
    <Context.Provider
      value={{
        user: state.user,
        isFetching: state.isFetching,
        error: state.error,
        dispatch,
      }}
    >
      {children}
    </Context.Provider>
  );
};

...

以下是我的 app.js，其中包含所有根节点 ...

import Home from "./Pages/home/Home";
import TopBar from "./components/topbar/TopBar";
import Single from "./Pages/single/Single";
import Write from "./Pages/write/Write";
import Settings from "./Pages/settings/Settings";
import Login from "./Pages/login/Login";
import Register from "./Pages/register/Register";
import { useContext } from "react";
import { Context } from "./context/Context";
import {
  BrowserRouter as Router,
  Routes,
  Route,
  Link,
  BrowserRouter
} from "react-router-dom"

function App() {
  const { user } = useContext(Context);
  return (
    <BrowserRouter >
      <TopBar />
      <Routes>
        <Route exact path="/" element={<Home />} />
        <Route path="register" element={user ? <Home /> : <Register />} />
        <Route path="login" element={ user ? <Home /> : <Login />} />
        <Route path="write" element={user ? <Write /> : <Register />} />
        <Route path="settings" element={user ? <Settings /> : <Register />} />
        <Route path="post/:postId" element={<Single />} />
      </Routes>
    </BrowserRouter >
  );
}

export default App;

...

有人可以帮我解决这个问题吗？

Answer 1

您显然是从上下文中获取默认值，而您的默认值没有 dispatch 函数。要使上下文正常工作，组件树上必须有一个上下文提供程序高于尝试使用上下文的组件。

您要么根本没有渲染 ContextProvider，要么在组件树的错误部分渲染它。

例如，以下将起作用：

const App = () => {
  return (
    <ContextProvider>
      <MyForm />
    <ContextProvider>
  ) 
}

const MyForm = () => {
  const { dispatch, isFetching } = useContext(Context);
  const handleSubmit = async (e) => {
     // ...
  }

  return (
    <div className="login">
      // ...
    </div>
  )
}

但这不会（提供者是消费者的child）：

const MyForm = () => {
  const { dispatch, isFetching } = useContext(Context);
  const handleSubmit = async (e) => {
     // ...
  }

  return (
    <ContextProvider>
      <div className="login">
        // ...
      </div>
    </ContextProvider>
  )
}

这也不会（提供者存在，但不是 MyForm 的祖先）

const App = () => {
  return (
    <div>
      <MyForm />
      <ContextProvider />
    </div>
  )
}

Uncaught (in promise) TypeError: dispatch is not a function useContext/useReducer

Uncaught (in promise) TypeError: dispatch is not a function useContext/useReducer

node.js

reactjs

react-hooks

react-context

use-context