为什么 "map" 不起作用？

Question

将创建博客 post，并且可以选择删除 post。为此，我正在使用钩子。

App.js:

import React, { useState } from 'react';

import Blog from './Blog';
import Createpost from './Createpost';

const App = () => {
    const [posts, setPosts] = useState('');
    const removePosts = (index) => {
        setPosts(posts.filter((post) => post.index !== index));
    };
    return (
        <div style={{ padding: 8 }} className="container">
            <br />
            <hr />
            {<Createpost posts={posts} setPosts={setPosts} />}
            <hr />
            <Blog postData={posts} removePosts={removePosts} />
        </div>
    );
};

export default App;

Createpost.js:

import React, { useState } from 'react';
const Createpost = ({ user, posts, setPosts }) => {
    const [title, setTitle] = useState('');
    const [content, setContent] = useState('');

    const handleTitle = (event) => {
        setTitle(event.target.value);
    };
    const handleContent = (event) => {
        setContent(event.target.value);
    };
    const handleCreate = (event) => {
        const newPost = { title, content, author: user };
        setPosts({ newPost, ...posts });
    };
    return (
        <form
            onSubmit={(e) => {
                e.preventDefault();
                handleCreate();
            }}
        >
            <div>
                author:<b>{user}</b>
            </div>
            <div>
                <label htmlFor="create-title">Title:</label>
                <input
                    tytpe="text"
                    value={title}
                    onChange={handleTitle}
                    name="create-
             title"
                    id="create-title"
                />
            </div>{' '}
            <textarea value={content} onChange={handleContent} />
            <input type="submit" value="Create" />
        </form>
    );
};

export default Createpost;

Blog.js:

import React, { useState } from 'react';
const BlogBody = (props) => {
    const rows = props.postData.map((post, index) => {
        const [title, author, content] = post;
        return (
            <React.Fragment key={index}>
                <h2>{title}</h2>
                <h5>
                    <i>{author}</i>
                </h5>
                <h3>{content}</h3>
                <br />
                <button onClick={() => props.removePosts(index)}>Delete</button>
                <hr />
            </React.Fragment>
        );
    });
    return <div>{rows}</div>;
};
const Blog = () => {
    const [postData, removePosts] = useState('');
    return (
        <div>
            <BlogBody postData={postData} removePosts={removePosts} />
        </div>
    );
};

export default Blog;

执行npm start后没有报错。但在浏览器中，TypeError: props.postData.map is not a function 显示在 Blog.js

有人可以帮我解决这个问题吗？我只是被困在这里似乎永远。

最近开始reactjs，昨天开始做hooks。所以请帮忙。

Answer 1

您正在创建 postData 作为字符串：

const [postData, removePosts] = useState('');

如果您希望它是一个数组，您应该更改初始值。

const [posts, setPosts] = useState([]);

// Add posts:
setPosts((prevPosts) => [...prevPosts, 'new post'])

Answer 2

Map函数只能用于数组。

在这里，您将 postData 的初始状态分配为字符串

即const [postData, removePosts] = useState('');

请将useState中的初始状态改为数组

即const [postData, removePosts] = useState([]);

为什么 "map" 不起作用？

why "map" is not wotking?

javascript

reactjs

react-hooks

react-hook-form