【Flutter】全角・半角判定しながら文字数カウント

import 'package:charset_converter/charset_converter.dart';

onChanged: (String value) async {
  final int _StringCount = 0;
  await Future.forEach(value.runes, (int rune) async {
    List<int> bytes = await CharsetConverter.encode('cp932', String.fromCharCode(rune));
    _StringCount += bytes.length;/// 2 = 全角, 1 = 半角
  });
  setState(() {
    _fullCount = _StringCount / 2;///全角文字数
  });
},