Basic Form Validator

import 'package:flutter/material.dart';
import 'package:gap/gap.dart';

final formKey = GlobalKey<FormState>();

Form(
  key: formKey,
  child: Column(
    crossAxisAlignment: CrossAxisAlignment.start,
    children: [
      TextFormField(
        validator: (value) {
          if (value == '') {
            return 'This Field is required';
          }
          return null;
        },
        decoration: const InputDecoration(
          hintText: 'Email',
          hintStyle: TextStyle(
            fontSize: 14,
            color: Colors.grey,
          ),
        ),
      ),
      const Gap(12),
      TextFormField(
        obscureText: true,
        autovalidateMode: AutovalidateMode.onUserInteraction,
        validator: (value) {
          if (value == '') {
            return 'This Field is required';
          }
          if (value!.length < 6) {
            return 'Minimum 6 characters';
          }
          return null;
        },
        decoration: const InputDecoration(
          hintText: 'Password',
          hintStyle: TextStyle(
            fontSize: 14,
            color: Colors.grey,
          ),
        ),
      ),
      const Gap(12),
      FilledButton(
        onPressed: () {
          if (formKey.currentState!.validate()) {
            print('saving...');
          }
        },
        child: const Text('Save'),
      ),
    ],
  ),
),