TypeError: Object is not iterable (cannot read property Symbol(Symbol.iterator))

Question

我试过运行这段代码，但它给我一个运行时错误

TypeError: Object is not iterable (cannot read property Symbol(Symbol.iterator))

这是代码。

import React, { useContext} from "react";
import { GlobalContext } from '../GlobalState';

const MediaCard = ({ songs, categotyTitle }) => {
  const [{}, dispatch] = useContext(GlobalContext);
  const setCurrentVideoSnippet = data => {
    dispatch({ type: "setCurrentVideoSnippet", snippet: data });
  };
export default MediaCard;

错误指向这行代码const [{}, dispatch] = useContext(GlobalContext);

GlobalState 代码

import React, { useReducer } from "react";

export const GlobalContext = React.createContext();

const initialState = {
  currentVideoSnippet: {}, 
};

const reducer = (state, action) => {
  switch (action.type) {
    case "setCurrentVideoSnippet":
      return {
        ...state,
        currentVideoSnippet: action.snippet
      };
 default:
      return state;
  }
};

export const GlobalState = props => {
  const globalState = useReducer(reducer, initialState);
  return (
    <GlobalContext.Provider value={globalState}>
      {props.children}
    </GlobalContext.Provider>
  );
};

Answer 1

您似乎忘记了使用您当前使用时创建的提供程序包装您的组件：

<GlobalState>
  <MediaCard />
</GlobalState>

Answer 2

我知道这并不能解决 OP 的问题，但是对于像我一样在这个页面上看到相同运行时间错误消息的人来说，我的问题是由于我导入的方式造成的GlobalContext 组件。

错误的方式： import GlobalContext from '../GlobalState';

正确方法： import { GlobalContext } from '../GlobalState';

这解决了我运行遇到的问题，但出现相同的错误消息。

Answer 3

下面是我的代码，它只是一个例子，向您展示为什么在您的代码中出现错误。

您创建的数据层没有包裹在整个网络应用程序的组件中，因此它无法被 MediaCard 组件识别...您需要做的只是进入您的index.js 并将 StateProvider 包裹在主应用程序周围

import React from 'react';
import ReactDOM from 'react-dom';
import './index.css';
import App from './App';
import * as serviceWorker from './serviceWorker';
import reducer, { initialState } from "./reducer";
import { StateProvider} from'./StateProvider';

ReactDOM.render(
  <React.StrictMode>
    <StateProvider initialState={ initialState } reducer={ reducer }>
    <App />
    </StateProvider>
  </React.StrictMode>,
  document.getElementById('root')
);

TypeError: Object is not iterable (cannot read property Symbol(Symbol.iterator))

TypeError: Object is not iterable (cannot read property Symbol(Symbol.iterator))

javascript

reactjs

react-hooks

state

use-reducer