Flutter:当字段在ListView中不可见时，不调用TextFormField验证器

import 'package:flutter/material.dart';

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

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

  @override
  Widget build(BuildContext context) {
    return ListView(
      children: [
        Form(
          key: _formKey,
          onChanged: () {
            _formKey.currentState.validate();
          },
          child: Column(
            children: [
              TextFormField(
                validator: (value) {
                  if (value.isEmpty) {
                    return 'Please enter some text';
                  }
                  return null;
                },
              ),
              // 其他表单字段
            ],
          ),
        ),
      ],
    );
  }
}