Flutter 验证码输入框

以下是一个简单的Flutter验证码输入框组件的实现示例：

import 'package:flutter/material.dart';
import 'package:flutter/services.dart';
 
class PinCodeTextField extends StatefulWidget {
  final ValueChanged<String> onTextChanged;
  final int pinLength;
 
  const PinCodeTextField({Key? key, required this.onTextChanged, this.pinLength = 4}) : super(key: key);
 
  @override
  _PinCodeTextFieldState createState() => _PinCodeTextFieldState();
}
 
class _PinCodeTextFieldState extends State<PinCodeTextField> {
  List<TextEditingController> _controllers = [];
  List<FocusNode> _focusNodes = [];
  String _pinCode = '';
 
  @override
  void initState() {
    super.initState();
    for (int i = 0; i < widget.pinLength; i++) {
      _controllers.add(TextEditingController());
      _focusNodes.add(FocusNode());
    }
  }
 
  @override
  void dispose() {
    for (var controller in _controllers) {
      controller.dispose();
    }
    for (var focusNode in _focusNodes) {
      focusNode.dispose();
    }
    super.dispose();
  }
 
  @override
  Widget build(BuildContext context) {
    return Row(
      children: List.generate(
        widget.pinLength,
        (index) => PinCodeField(
          controller: _controllers[index],
          focusNode: _focusNodes[index],
          onChanged: (value) {
            if (index + 1 < widget.pinLength) {
              FocusScope.of(context).requestFocus(_focusNodes[index + 1]);
            }
            _pinCode = _pinCode.substring(0, index) + value + _pinCode.substring(index + 1);
            widget.onTextChanged(_pinCode);
          },
          textInputAction: index == widget.pinLength - 1 ? TextInputAction.done : TextInputAction.next,
          onSubmitted: (value) {
            if (index + 1 < widget.pinLength) {
              _focusNodes[index + 1].requestFocus();
            }
          },
        ),
      ),
    );
  }
}
 
class PinCodeField extends StatefulWidget {
  final TextEditingController controller;
  final FocusNode focusNode;
  final ValueChanged<String> onChanged;
  final TextInputAction textInputAction;
  final ValueChanged<String> onSubmitted;
 
  const PinCodeField({
    Key? key,
    required this.controller,
    required this.focusNode,
    required this.onChanged,
    required this.textInputAction,
    required this.onSubmitted,
  }) : super(key: key);
 
  @override
  _PinCodeFieldState createState() => _PinCodeFieldState();
}
 
class _PinCodeFieldS