An example of getting all field values in a Form.

main.dart

import 'package:flutter/material.dart';

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      debugShowCheckedModeBanner: false,
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

class MyHomePage extends StatelessWidget {
  MyHomePage({
    Key? key,
    required this.title,
  }) : super(key: key);

  final String title;
  final GlobalKey<FormState> _formKey = GlobalKey();

  final List<GlobalKey> _fieldKeys = <GlobalKey>[
    GlobalKey(),
    GlobalKey(),
    GlobalKey(),
    GlobalKey(),
  ];

  void _onPressed() {
    final FormState? formState = _formKey.currentState;
    if (formState == null || !formState.validate() == true) return;

    // With submit:
    // final data = formState.submit();
    // final newPost = Post.fromJson(data);

    // Without submit:
    final Map<GlobalKey, dynamic> data = <GlobalKey, dynamic>{};
    for (GlobalKey fieldKey in _fieldKeys) {
      final FormFieldState<dynamic> formFieldState = fieldKey.currentState as FormFieldState<dynamic>;
      if (formFieldState.value != null) {
        data[fieldKey] = formFieldState.value;
      }
    }
    print('data: $data');
  }
  
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(title),
      ),
      body: Center(
        child: Form(
          key: _formKey,
          child: SingleChildScrollView(
            child: Column(
              crossAxisAlignment: CrossAxisAlignment.start,
              children: _fieldKeys.map((GlobalKey fieldKey) {
                return TextFormField(
                  key: fieldKey,
                );
              }).toList(),
            ),
          ),
        ),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: _onPressed,
        tooltip: 'Increment',
        child: const Icon(Icons.add),
      ),
    );
  }
}