React Redux Reducer：“this.props.tasks.map 不是函数”错误

Question

我正在制作一个 React Redux 示例；但是，我遇到了一个问题并收到以下错误：

TypeError: this.props.tasks.map 不是函数 [了解更多]

我尝试了很多事情，但我似乎无法理解为什么这不起作用。我相信这是 allReducers 从 Tasks 函数映射任务的时候。我已经来回修复了这个错误，但它会抱怨它是未定义的。我会解决这个问题并回到这个问题。任何帮助，将不胜感激。我确定我犯了一个简单的错误。以下是我的以下文件

App.js

import React from 'react';
import TaskBoard from "../containers/task-board";
require('../../scss/style.scss');

const App = () => (
    <div>
        <h2>Task List</h2>
        <hr />
        <TaskBoard/>
    </div>
);

export default App;

index.js

    import {combineReducers} from 'redux';
    import {Tasks} from './reducer-tasks';
    const allReducers = combineReducers({
        tasks: Tasks
    });

    export default allReducers

task-board.js

    import React, {Component} from 'react';
    import {bindActionCreators} from 'redux';
    import {connect} from 'react-redux';
    import {deleteTaskAction} from '../actions/ActionIndex';
    import {editTaskAction} from '../actions/ActionIndex';
    class TaskBoard extends Component {
        renderList() {
            return this.props.tasks.map((task) => {
                if(task.status == "pending"){
                    return (<li key={task.id}>
                        {task.id} {task.description}
                        <button type="button">Finish</button>
                        <button type="button">Edit</button>
                        <button onClick={() => this.props.deleteTask(task)} type="button">Delete</button>
                    </li>
                );
            }
        });
    }
    render() {
        if (!this.props.tasks) {
            console.log(this.props.tasks);
            return (<div>You currently have no tasks, please first create one...</div>);
        }
        return (
            <div>
                {this.renderList()}
            </div>
        );
    }
}
    function mapStateToProps(state) {
        return {
            tasks: state.tasks
        };
    }
    function matchDispatchToProps(dispatch){
        return bindActionCreators(
        {
            deleteTask: deleteTaskAction,
            editTask: editTaskAction
        }, dispatch)
    }
    export default connect(mapStateToProps,matchDispatchToProps)(TaskBoard);

reducer-tasks.js

const initialState = {
	tasks: [
        {
            id: 1,
            description: "This is a task",
            status: "pending"
        },
        {
            id: 2,
            description: "This is another task",
            status: "pending"
        },
        {
            id: 3,
            description: "This is an easy task",
            status: "pending" 

        }
	]
}

export function Tasks (state = initialState, action) {
    switch (action.type) {
        case 'ADD_TASK':
            return Object.assign({}, state, {
            	tasks: [
            		...state.tasks,
            		{
            			description: action.text,
            			status: action.status
            		}
            	]
            })
            break;

        case 'EDIT_TASK':
            return action.payload;
            break;

        case 'DELETE_TASK':
            return Object.assign({}, state, {
            	status: action.status
            })
            break;
    }

    return state;
}

actionindex.js

    export const addTaskAction = (task) => {
        return {
            type: 'ADD_TASK',
            text: "Here is a sample description",
            status: "pending"
        }
    };
    export const deleteTaskAction = (task) => {
        return {
            type: 'DELETE_TASK',
            status: "deleted"
        }
    };
    export const editTaskAction = (task) => {
        return {
            type: 'EDIT_TASK',
            payload: task
        }
    };

Answer 1

这是因为函数'map'只能用于数组，不能用于对象。

如果您在 task-board.js 的渲染函数中打印出 this.props.tasks，您会看到它是一个包含任务数组的 OBJECT，而不是实际的任务数组本身。

所以要解决这个问题很容易，而不是：

    return this.props.tasks.map((task) => {

这是

    return this.props.tasks.tasks.map((task) => {

然后就可以了

Answer 2

根据你的reducer组成，你的initialState应该是：

const initialState = [
    {
        id: 1,
        description: "This is a task",
        status: "pending"
    },
    {
        id: 2,
        description: "This is another task",
        status: "pending"
    },
    {
        id: 3,
        description: "This is an easy task",
        status: "pending" 

    }
]

Answer 3

如果您在获取数据之前尝试渲染，请检查服务器代码。如果是这种情况，redux/react 会抛出 .map is not a function。

始终获取数据，使用中间件，然后尝试从服务器渲染客户端。

我在 redux 中遇到了同样的问题，问题是我在渲染客户端后尝试获取数据