reactjs - React 独特的 "key"错误

Question

我正在浏览 React 中的待办事项列表教程，并遇到了以下错误，我花了很长时间，只是找不到错误。这是错误和组件的代码，这是是类(class)存储库的代码(问题出现在此提交上):

https://github.com/andrewjmead/react-course-todo-app/commit/0521f151705f78cb9f8d69262eb093f1431cb9ca

非常感谢任何帮助。

警告:数组或迭代器中的每个子项都应该有一个唯一的“key”属性。检查TodoList的渲染方法。请参阅 fb.me/react-warning-keys 了解更多信息。

终端中还有一个错误，对于 TOGGLE_TODO 情况下的扩展运算符

return {
...todo, // here
completed: nextCompleted,
completedAt: nextCompleted ? moment().unix() : undefined
};

var React = require('react');
var { connect } = require('react-redux');
import Todo from 'Todo';
var TodoAPI = require('TodoAPI');

export var TodoList = React.createClass ({
    render: function() {
        var { todos, showCompleted, searchText } = this.props;
        var renderTodos = () => {
            if(todos.length === 0) {
                return (
                    <p className="container__message">No tasks</p>
                );
            }
            return TodoAPI.filterTodos(todos, showCompleted, searchText).map((todo) => {
                return (
                    //add unique key prop to keep track of individual components
                    <Todo key={todo.id} {...todo} />
                );
            });
        };
        return (
            <div>
                {renderTodos()}
            </div>
        );  
    }
});

export default connect(
    (state) => {
        return state;
    }
)(TodoList);

reducer :

var uuid = require('uuid');
var moment = require('moment');

export var searchTextReducer = (state = '', action) => {
    switch (action.type) {
        case 'SET_SEARCH_TEXT':
            return action.searchText;
        default: 
            return state;
    };
};

export var showCompletedReducer = (state = false, action) => {
    switch (action.type) {
        case 'TOGGLE_SHOW_COMPLETED':
            return !state;
        default: 
            return state;
    };    
};

export var todosReducer = (state = [], action) => {
    switch(action.type) {
        case 'ADD_TODO':
            return [
                ...state,
                {
                    text: action.text,
                    id: uuid(),
                    completed: false,
                    createdAt: moment().unix(),
                    completedAt: undefined                   
                }
            ];
        case 'TOGGLE_TODO':
            return state.map((todo) => {
                if(todo.id === action.id) {
                    var nextCompleted = !todo.completed;

                    return {
                        ...todo,
                        completed: nextCompleted,
                        completedAt: nextCompleted ? moment().unix() : undefined
                    };
                } else {
                    return todo;
                }
            });
        case 'ADD_TODOS':
            return [
                ...state,
                ...action.todos
            ];
        default: 
            return state;
    }
};


Webpack:

var webpack = require('webpack');

module.exports = {
  entry: [
    'script!jquery/dist/jquery.min.js',
    'script!foundation-sites/dist/js/foundation.min.js',
    './app/app.jsx'
  ],
  externals: {
      jquery: 'jQuery'
  },
  plugins: [
      new webpack.ProvidePlugin({
          '$': 'jquery',
          'jQuery': 'jquery'
      })
  ],
  output: {
    path: __dirname,
    filename: './public/bundle.js'
  },
  resolve: {
    root: __dirname,
    modulesDirectories: [
        'node_modules',
        './app/components',
        './app/api'
    ],
    alias: {
        applicationStyles: 'app/styles/app.scss',
        actions: 'app/actions/actions.jsx',
        reducers: 'app/reducers/reducers.jsx',
        configureStore: 'app/store/configureStore.jsx'
    },
    extensions: ['', '.js', '.jsx']
  },
  module: {
    loaders: [
      {
        loader: 'babel-loader',
        query: {
          presets: ['react', 'es2015']
        },
        test: /\.jsx?$/,
        exclude: /(node_modules|bower_components)/
      }
    ]
  },
  devtool: 'cheap-module-eval-source-map'
};

Answer 1

在 React 中，当您渲染多个相同的组件(在您的例子中是待办事项)时，您需要为每个组件添加一个唯一的键，这是因为 React 需要知道如何在虚拟中处理它们统治。

您可以采取多种措施来解决此问题:

1. 在 for 循环中，创建一个索引变量，并在每次循环结束时将其加 1，然后将其设置为每个渲染组件的键。

2. 如果您从 API 获取待办事项，请为每个待办事项设置一个 ID 并将其用作组件 key 。

3. 使用随机数生成器为每个待办事项设置唯一的 key 。

最好的方法是#2和#3，我发现在你的情况下，你正在尝试执行#2(通过todo id设置 key )，但我认为它是未定义的，请检查它。

另一个解决方案是使用uuid在每个渲染的组件/todo 上。

为此，您可以安装 node-uuid .

运行:npm i --save node-uuid

然后在文件中进行导入:import uuid from 'node-uuid' 或 const uuid = require('node-uuid')

现在将您的代码更改为如下所示:

return TodoAPI.filterTodos(todos, showCompleted, searchText).map((todo) => {
  return (
    //add unique key prop to keep track of individual components
    <Todo key={uuid()} {...todo} />
  );
});

然后就可以开始了。