Flutter文本字段，在输入文本时自动扩展，然后在达到一定高度时开始滚动文本

import 'package:flutter/material.dart';

class AutoExpandingTextField extends StatefulWidget {
  @override
  _AutoExpandingTextFieldState createState() => _AutoExpandingTextFieldState();
}

class _AutoExpandingTextFieldState extends State<AutoExpandingTextField> {
  final TextEditingController _textEditingController = TextEditingController();
  final ScrollController _scrollController = ScrollController();

  @override
  Widget build(BuildContext context) {
    return Column(
      children: [
        Expanded(
          child: SingleChildScrollView(
            controller: _scrollController,
            child: Container(
              constraints: BoxConstraints(
                maxHeight: 200, // 设置最大高度
              ),
              child: TextField(
                controller: _textEditingController,
                maxLines: null, // 设置最大行数为null，使得文本能够自动换行
                onChanged: (value) {
                  setState(() {}); // 监听文本变化，触发重新构建界面
                  WidgetsBinding.instance.addPostFrameCallback((_) {
                    _scrollController.animateTo(
                      _scrollController.position.maxScrollExtent, // 滚动到底部
                      duration: Duration(milliseconds: 300),
                      curve: Curves.easeInOut,
                    );
                  });
                },
              ),
            ),
          ),
        ),
      ],
    );
  }
}