Error in json parsing on flutter. type '_InternalLinkedHashMap<String, dynamic>' is not a subtype of type 'ResultData' in type cast

Question

I have json as below.

{  
   "result_data":{  
      "id":"b57457b0-4f73-11e8-92ae-01912016d38c",
      "rates":[  
         {  },
         {  }
      ]
   }
}

I want to parse and below is my code to parse it. To get the "result_data"

class RootModel {
  ResultData resultData;

  RootModel(this.resultData);

  RootModel.fromJSON(Map<String, dynamic> response) {
    var list = response['result_data'] as ResultData;
    print(list.runtimeType);
  }
}

To parse the result data object.

class ResultData {
  String id;
  List<Rate> rates;
  ResultData(this.id, this.rates);

  ResultData.fromJSON(Map<String, dynamic> parsedJson) {
    this.id = parsedJson['id'] as String;
    this.rates = (parsedJson['rates'] as List)
        .map((json) => Rate.fromJSON(json))
        .toList();
  }
}

Further rates model has also other models and list of models. The error I am getting for the above code is:

 E/flutter: [ERROR:flutter/shell/common/shell.cc(184)] Dart Error: Unhandled exception:
    type '_InternalLinkedHashMap<String, dynamic>' is not a subtype of type 'ResultData' in type cast
    #0      new RootModel.fromJSON (package:movies_streams/models/RootModel.dart:16:40)

Solution 1

You can't cast map to ResultData.

class RootModel {
  ResultData resultData;

  RootModel(this.resultData);

  RootModel.fromJSON(Map<String, dynamic> response) {
//    var list = response['result_data'] as ResultData;
    var list = ResultData.fromJSON(response['result_data']);
    print(list.runtimeType);
  }
}

Solution 2

There is no magic happening for JSON deserialization. You have to invoke the fromJSON yourself, instead of just casting:

class RootModel {
  ResultData resultData;

  RootModel(this.resultData);

  RootModel.fromJSON(Map<String, dynamic> response)
    : resultData =  ResultData.fromJSON(response['result_data'] as Map<String, dynamic>);

}