Flutter API Call Error: (Map<String, dynamic>) is not a subtype of type '(dynamic)

Question

I want to load some data from my API.

I build the model for the data I want to receive like this:

  int? id;
  int? createdAt;
  int? eventsId;
  int? userId;
  String? deleteindex;
  int? pferdeId;
  Vertreter? vVertreter;

  VertreterModell(
      {this.id,
      this.createdAt,
      this.eventsId,
      this.userId,
      this.deleteindex,
      this.pferdeId,
      this.vVertreter});

  VertreterModell.fromJson(Map<String, dynamic> json) {
    id = json['id'];
    createdAt = json['created_at'];
    eventsId = json['events_id'];
    userId = json['user_id'];
    deleteindex = json['deleteindex'];
    pferdeId = json['pferde_id'];
    vVertreter = json['_vertreter'] != null
        ? new Vertreter.fromJson(json['_vertreter'])
        : null;
  }

  Map<String, dynamic> toJson() {
    final Map<String, dynamic> data = new Map<String, dynamic>();
    data['id'] = this.id;
    data['created_at'] = this.createdAt;
    data['events_id'] = this.eventsId;
    data['user_id'] = this.userId;
    data['deleteindex'] = this.deleteindex;
    data['pferde_id'] = this.pferdeId;
    if (this.vVertreter != null) {
      data['_vertreter'] = this.vVertreter!.toJson();
    }
    return data;
  }
}

class Vertreter {
  String? name;
  Profilbild? profilbild;

  Vertreter({this.name, this.profilbild});

  Vertreter.fromJson(Map<String, dynamic> json) {
    name = json['name'];
    profilbild = json['profilbild'] != null
        ? new Profilbild.fromJson(json['profilbild'])
        : null;
  }

  Map<String, dynamic> toJson() {
    final Map<String, dynamic> data = new Map<String, dynamic>();
    data['name'] = this.name;
    if (this.profilbild != null) {
      data['profilbild'] = this.profilbild!.toJson();
    }
    return data;
  }
}

class Profilbild {
  String? url;

  Profilbild({this.url});

  Profilbild.fromJson(Map<String, dynamic> json) {
    url = json['url'];
  }

  Map<String, dynamic> toJson() {
    final Map<String, dynamic> data = new Map<String, dynamic>();
    data['url'] = this.url;
    return data;
  }
}

and my API Code looks like this:

    const storage = FlutterSecureStorage();
    var token = await storage.read(key: "_authToken");
    var url = Uri.parse('${Constants.BASE_URL}/vertretung/vertreter');

    var headers = {
      'Content-Type': 'application/json',
      'Accept': 'application/json',
      'Authorization': 'Bearer $token',
    };

    var res = await http.get(url, headers: headers);
    final result = json.decode(res.body);
    print(result);
    return result.map<VertreterModell>(VertreterModell.fromJson).toList();
  }

Every time I call the API i get an error:

type '(Map<String, dynamic>) => VertreterModell' is not a subtype of type '(dynamic) => VertreterModell' of 'f'

Any ideas what I am doing wrong? It works for other api functions I made. Thanks in advance!

PurplePolyhedron · Accepted Answer · 2023-01-20 06:13:33Z

1

result has runtime type List<dynamic>, so it can't be mapped using a function that takes Map<String, dynamic> parameter.

Also since result has type dynamic but has runtime type of List<dynamic>, you can still use map, but there is no static analysis about the usage of it.

You can try

result.map<VertreterModell>((data) => VertreterModell.fromJson(data) ).toList();

Since data have type dynamic here.

    final oldList = jsonDecode('[{"a": "1"},{"b": "2"},{"c": "3"}]');
    print(oldList.runtimeType); // List<dynamic>

    //runtime error, but no static analysis error
    oldList.map<MyClass>(MyClass.fromJson).toList();

    //static analysis error
    (oldList as List<dynamic>).map<MyClass>(MyClass.fromJson).toList();

    //no error
    final newList = oldList.map<MyClass>((data) => MyClass.fromJson(data)).toList();
    print(newList);

edited Jan 20, 2023 at 6:13

answered Jan 20, 2023 at 6:07

PurplePolyhedron

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Comments

Romil Mavani · Accepted Answer · 2023-01-20 06:12:40Z

Once try to create model using this tool. https://ashamp.github.io/jsonToDartModel/

And use this method for api calling

const storage = FlutterSecureStorage();
    var token = await storage.read(key: "_authToken");
    var url = Uri.parse('${Constants.BASE_URL}/vertretung/vertreter');

    var headers = {
      'Content-Type': 'application/json',
      'Accept': 'application/json',
      'Authorization': 'Bearer $token',
    };

    var res = await http.get(url, headers: headers);
    final result = json.decode(res.body);
    print(result);
    YourModel yourModelName = YourModel.fromJson(result);
    ///return if you want data usign **yourModelName** object.
    return yourModelName;
  }

I Hope this things are solve your issue.

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