解决React列表状态更新不触发重渲染：受控组件在输入管理中的应用

class ChatPage extends Component {
    constructor(props) {
        super(props);
        this.state = {
            userMessages: [[0, 'First example message'], [1, 'Second msg']],
            userMessageNextId: 2,
        };
        this.sendMessage = this.sendMessage.bind(this);
    }

    render() {
        return (
            <div className="chat-page mb-5">
                {/* ... 其他消息显示部分 ... */}
                <div className="input-container">
                    <div className="input-group">
                        <input type="text" className="form-control" id="message-text" placeholder="Type something..."/>
                        <button className="btn btn-primary" onClick={this.sendMessage}>Send</button>
                    </div>
                </div>
            </div>
        )
    }

    sendMessage() {
        // 问题所在：直接操作DOM获取输入值
        const messageText = document.querySelector("#message-text").value;
        if (!messageText?.trim()) return;
        this.setState(state => {
            const newArray = [...state.userMessages, [state.userMessageNextId, messageText]];
            return {
                userMessages: newArray,
                userMessageNextId: state.userMessageNextId + 1
            }
        });
        // 即使setState触发了渲染，但输入框的值不是由state控制的，所以它不会被清空或更新
    }
}

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: '' // 1. 在状态中添加一个字段来存储输入框的值
        };
        this.sendMessage = this.sendMessage.bind(this);
        this.handleInputChange = this.handleInputChange.bind(this); // 绑定事件处理器
    }

    render() {
        console.log(this.state.userMessages); // 调试时可以看到userMessages的变化
        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>
                        {/* 渲染用户发送的消息列表 */}
                        {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} // 2. 将输入框的value绑定到state
                            onChange={this.handleInputChange} // 3. 添加onChange事件处理器
                        />
                        <button className="btn btn-primary" onClick={this.sendMessage}>
                            Send
                        </button>
                    </div>
                </div>
            </div>
        );
    }

    sendMessage() {
        // 4. 不再使用document.querySelector，直接使用state中的messageText
        if (!this.state.messageText.trim()) return;

        this.setState((state) => {
            console.log('Setting state...');
            const newArray = [...state.userMessages, [state.userMessageNextId, state.messageText]];
            return {
                userMessages: newArray,
                userMessageNextId: state.userMessageNextId + 1,
                messageText: '' // 4. 发送消息后清空输入框
            };
        });
    }

    handleInputChange(event) {
        // 3. onChange事件处理器：更新state中的messageText
        this.setState({ messageText: event.target.value });
    }
}

export default ChatPage;