Flutter TextFormField:如何将类函数设置为TextFormField验证器的函数？

class FormValidator {
  String validateInput(String value) {
    if (value.isEmpty) {
      return '请输入有效的内容';
    }
    return null;
  }
}

class MyForm extends StatefulWidget {
  @override
  _MyFormState createState() => _MyFormState();
}

class _MyFormState extends State<MyForm> {
  final _formKey = GlobalKey<FormState>();
  final _validator = FormValidator();

  @override
  Widget build(BuildContext context) {
    return Form(
      key: _formKey,
      child: TextFormField(
        validator: _validator.validateInput,
        // 其他属性...
      ),
    );
  }
}