Parsing from json call to map in flutter

Question

Hi the following dart code in flutter, make a rest call to a node.js server returning a map of values ​​in a map. When I run the code, however, the exception below is raised. How can I go about solving this? Below is an example of json values ​​returning from the rest server in node.js.

Dart Code:

  static Future<Map> Ricerca(Utente u, int IdCantiere, String NomeCantiere,
      String RagioneSociale, bool isUtente) async {

    Map ret;
    Map map = {
      'IdUtente': u.GetIdUtente(),
      'IdCantiere': IdCantiere,
      'NomeCantiere': NomeCantiere,
      'RagioneSociale': RagioneSociale,
      'CheckBoxCantieriCreatiDaUtenteLoggato': isUtente
    };
    String value = await apiRequest("/cantieri/ricerca", map);

    ret = json.decode(value);
          return ret;
  }

Exception:

[VERBOSE-2:ui_dart_state.cc(157)] Unhandled Exception: type 'List<dynamic>' is not a subtype of type 'Map<dynamic, dynamic>'
#0      CantiereController.Ricerca (package:MyApp/Controller/Cantiere.dart:28:5)
<asynchronous suspension>
#1      Cantiere.ricerca (package:MyApp/Model/Cantiere.dart:18:142)
#2      inizializzaValori (package:MyApp/View/Cantieri/training_screen.dart:25:38)
<asynchronous suspension>
#3      _TrainingScreenState.initState (package:MyApp/View/Cantieri/training_screen.dart:47:5)
#4      StatefulElement._firstBuild (package:flutter/src/widgets/framework.dart:4355:58)
#5      ComponentElement.mount (package:flutter/src/widgets/framework.dart:4201:5)
#6      Element.inflateWidget (package:flutter/src/widgets/framework.dart:3194:14)
#7      MultiChildRenderObjectElement.mount (package:flutter/src/widgets/framework.dart:5551:32)
#8      Element.inflateWidget (package:flutter/src/widgets/framework.dart:3194:14)
#9      Element.updateChild (package:flutter/src/widgets/framework.dart:2988<…>MyApp

ApiRest.dart Code:

Future<String> apiRequest(String urlpassed, Map jsonMap) async {
  //Give server and port
  String server = await Storage.leggi("Server");
  String porta = await Storage.leggi("Porta");

  var url=""+server+":"+porta;

  url=url+urlpassed;
  HttpClient httpClient = new HttpClient();

  HttpClientRequest request = await httpClient.postUrl(Uri.parse(url));
  request.headers.set('content-type', 'application/json');
  request.add(utf8.encode(json.encode(jsonMap)));
  HttpClientResponse response = await request.close();

  String reply = await response.transform(utf8.decoder).join();
  httpClient.close();
  return reply;
}

JSON Example:

[
    {
        "IdCantiere": 4,
        "IdCliente": 40,
        "Filiale": "SEDE",
        "RagioneSociale": "dsdso",
        "NomeCantiere": "sala sdsd",
        "DataCreazioneCantiere": "2017-08-04T18:20:31.333Z",
        "Tipologia": "Consuntivo",
        "StatoCantiere": "Chiuso",
        "StatoFatturazione": 1,
        "DescrizioneEstesa": "sddsdsd"
    },
    {
        "IdCantiere": 5,
        "IdCliente": 204,
        "Filiale": "SEDE",
        "RagioneSociale": "sdsds",
        "NomeCantiere": "manutenzione allarme",
        "DataCreazioneCantiere": "2017-08-04T18:27:42.017Z",
        "Tipologia": "Consuntivo",
        "StatoCantiere": "Chiuso",
        "StatoFatturazione": 1,
        "DescrizioneEstesa": "manutenzione impianto allarme AVS"
    },
    {
        "IdCantiere": 6,
        "IdCliente": 140,
        "Filiale": "SEDE",
        "RagioneSociale": "Psdsddo",
        "NomeCantiere": "Ristrutturazione terremoto",
        "DataCreazioneCantiere": "2017-08-07T17:45:15.347Z",
        "Tipologia": "Consuntivo",
        "StatoCantiere": "Chiuso",
        "StatoFatturazione": 1,
        "DescrizioneEstesa": "        stampato 10/01/19"
    }
]

Answer 1

Your JSON is returning a List not a Map. Keep it a List:

List<dynamic> ret = json.decode(value);

Then you can change the list type:

List<Map<String, dynamic>> data = ret.map((value) => value as Map<String, dynamic>).toList();

Answer 2

The rest service is returning a list of Map and you method is awaiting for just a Map, probably change your method like the code below could help

static Future<List<Map<String,dynamic>>> Ricerca(Utente u, int IdCantiere, String NomeCantiere,
      String RagioneSociale, bool isUtente) async {

    Map ret;
    Map map = {
      'IdUtente': u.GetIdUtente(),
      'IdCantiere': IdCantiere,
      'NomeCantiere': NomeCantiere,
      'RagioneSociale': RagioneSociale,
      'CheckBoxCantieriCreatiDaUtenteLoggato': isUtente
    };
    String value = await apiRequest("/cantieri/ricerca", map);

    ret = json.decode(value);
          return ret;
  }

Answer 3

Try

Map<String, dynamic> ret = json.decode(value);