my take at the standard flutter autocomplete while unmarshaling a json with a custom type

RawAutocompleteEddy.dart

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

class RawAutocompleteEddy extends StatelessWidget {
  const RawAutocompleteEddy({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        appBar: AppBar(
          title: const Text('my take at RawAutocomplete \nCustomType unmarshal'),
        ),
        body: const Center(
          child: AutocompleteCustomTypeExample(),
        ),
      ),
    );
  }
}

/*
  {
    "match": "Badia Polesine",
    "tipo": "comune",
    "idprovincia": 29,
    "provincia": "Rovigo",
    "idcomune": 2770,
    "comune": "Badia Polesine",
    "zonaid": null,
    "zona": null
  },

*/
// An example of a type that someone might want to autocomplete a list of.
@immutable
class Posto {
  const Posto({
    required this.match,
    required this.tipo,
    required this.idprovincia,
    required this.provincia,
    required this.idcomune,
    required this.comune,
    required this.zonaid,
  });

  final String match;
  final String tipo;
  final int idprovincia;
  final String provincia;
  final int idcomune;
  final String comune;
  final int zonaid;

  factory Posto.fromJson(Map<String, dynamic> json) {
    return Posto(
      match: json['match'] ?? "",
      tipo: json['tipo'] ?? "",
      idprovincia: json['idprovincia'] ?? 0,
      provincia: json['provincia'] ?? "",
      idcomune: json['idcomune'] ?? 0,
      comune: json['comune'] ?? "",
      zonaid: json['zonaid'] ?? 0,
    );
  }

  @override
  String toString() {
    return '$match, $tipo';
  }

  @override
  bool operator ==(Object other) {
    if (other.runtimeType != runtimeType) {
      return false;
    }
    return other is Posto && other.match == match && other.tipo == tipo;
  }

  @override
  int get hashCode => hashValues(tipo, match);
}

class AutocompleteCustomTypeExample extends StatelessWidget {
  const AutocompleteCustomTypeExample({Key? key}) : super(key: key);

  static const String dati =
      '[{"match":"Centocelle","tipo":"zona","idprovincia":58,"provincia":"Roma","idcomune":6915,"comune":"Roma","zonaid":141,"zona":"Centocelle"},{"match":"Centro Direzionale Centocelle","tipo":"zona","idprovincia":58,"provincia":"Roma","idcomune":6915,"comune":"Roma","zonaid":144,"zona":"Centro Direzionale Centocelle"}]';

  static List<Posto> _userOptions = <Posto>[];

  static String _displayStringForOption(Posto option) => option.match;

  @override
  Widget build(BuildContext context) {
    return RawAutocomplete<Posto>(
      optionsBuilder: (TextEditingValue textEditingValue) {
        debugPrint("azione ${textEditingValue.text.toLowerCase()}"); // TODO: this would be a good time to query new data
        final parsed = json.decode(dati).cast<Map<String, dynamic>>();
        _userOptions = parsed.map<Posto>((json) => Posto.fromJson(json)).toList();
        return _userOptions.where((Posto option) {
          // Search based on Posto.toString, which includes both match and
          // tipo, even though the display string is just the match.
          return option.toString().contains(textEditingValue.text.toLowerCase());
        });
      },
      displayStringForOption: _displayStringForOption,
      fieldViewBuilder: (BuildContext context, TextEditingController textEditingController, FocusNode focusNode, VoidCallback onFieldSubmitted) {
        return TextFormField(
          controller: textEditingController,
          focusNode: focusNode,
          onFieldSubmitted: (String value) {
            onFieldSubmitted();
          },
        );
      },
      optionsViewBuilder: (BuildContext context, AutocompleteOnSelected<Posto> onSelected, Iterable<Posto> options) {
        return Align(
          alignment: Alignment.topLeft,
          child: Material(
            elevation: 4.0,
            child: SizedBox(
              height: 200.0,
              child: ListView.builder(
                padding: const EdgeInsets.all(8.0),
                itemCount: options.length,
                itemBuilder: (BuildContext context, int index) {
                  final Posto option = options.elementAt(index);
                  return GestureDetector(
                    onTap: () {
                      onSelected(option);
                    },
                    child: ListTile(
                      title: Text(_displayStringForOption(option)),
                    ),
                  );
                },
              ),
            ),
          ),
        );
      },
    );
  }
}