React列表状态更新与受控组件：确保UI同步渲染的关键

// 原始问题代码片段（存在问题）
sendMessage() {
    const messageText = document.querySelector("#message-text").value; // 直接访问DOM
    if (!messageText?.trim()) return;
    this.setState(state => {
        const newArray = [...state.userMessages, [state.userMessageNextId, messageText]];
        return {
            userMessages: newArray,
            userMessageNextId: state.userMessageNextId + 1
        }
    });
}

import React, { Component } from 'react';

// 假设 MessageGroup 和 Message 组件已定义
// import MessageGroup from './MessageGroup';
// import Message from './Message';

class ChatPage extends Component {
    constructor(props) {
        super(props);
        this.state = {
            userMessages: [[0, 'First example message'], [1, 'Second msg']],
            userMessageNextId: 2,
            messageText: '' // 新增：用于控制输入框的state
        };
        this.sendMessage = this.sendMessage.bind(this);
        this.handleInputChange = this.handleInputChange.bind(this); // 绑定事件处理器
    }

    render() {
        console.log("Current messages in state:", this.state.userMessages);
        return (
            <div className="chat-page mb-5">
                <div className="messages-container">
                    <MessageGroup sentBy="Juan">
                        <Message>This is the first message</Message>
                        <Message>This is the second message</Message>
                    </MessageGroup>
                    <MessageGroup sentByUser>
                        {/* 映射 userMessages 状态到 Message 组件 */}
                        {this.state.userMessages.map((val) => (
                            <Message key={val[0]}>{val[1]}</Message>
                        ))}
                    </MessageGroup>
                </div>
                <div className="input-container">
                    <div className="input-group">
                        <input
                            type="text"
                            className="form-control"
                            id="message-text"
                            placeholder="Type something..."
                            value={this.state.messageText} // 绑定输入框的value到state
                            onChange={this.handleInputChange} // 绑定onChange事件
                        />
                        <button className="btn btn-primary" onClick={this.sendMessage}>
                            Send
                        </button>
                    </div>
                </div>
            </div>
        );
    }

    // 处理输入框内容变化的事件
    handleInputChange(event) {
        this.setState({ messageText: event.target.value }); // 更新messageText状态
    }

    // 发送消息的逻辑
    sendMessage() {
        if (!this.state.messageText.trim()) return; // 使用state中的messageText
        this.setState((state) => {
            console.log('Setting state for new message...');
            const newArray = [...state.userMessages, [state.userMessageNextId, state.messageText]];
            return {
                userMessages: newArray,
                userMessageNextId: state.userMessageNextId + 1,
                messageText: '' // 清空输入框，通过更新state实现
            };
        });
    }
}

export default ChatPage;