Widget _maxLengthType(BuildContext context) {
    return TDTextarea(
      controller: controller[3],
      label: '标签文字',
      hintText: '请输入文字',
      maxLines: 4,
      minLines: 4,
      maxLength: 500,
      indicator: true,
      onChanged: (value) {
        setState(() {});
      },
    );
  }