Dio.get – Unhandled Exception: type '_InternalLinkedHashMap<String, dynamic>' is not a subtype of type 'String' in Flutter/Dart

With Dio, I make a request like this:

//Airtable (find a record)
  void airtableFind() async {
    try {
      final response = await Dio().get(
        'https://api.airtable.com/v0/'+projectBase+'/'+recordName,
        queryParameters: {
          // 'filterByFormula': 'SEARCH("Cactus",{Name})' // Searches the value 'Cactus' in the {'Short description'} field.
          'filterByFormula': 'SEARCH('+'"'+testName+'"'+',{Name})' // Searches the value 'Cactus' in the {'Short description'} field.
          // 'filterByFormula': 'SEARCH('+testName+',{Name})' // Searches the value 'Cactus' in the {'Short description'} field.
        },
        options: Options(
          contentType: 'Application/json',
          headers: {
            'Authorization': 'Bearer'+' '+apiKey,
            'Accept': 'Application/json',
          },
        ),
      );

      // TODO: Whatever you want to do with the response. A good practice is to transform it into models and than work with them
      print(response);
      // var decodedString = json.decode(response.data.toString());
      final decodedString = json.decode(response.data);
      print(decodedString);

      // print(decodedString['records'][0]['id']);
      // String id = decodedString['records'][0]['id'];

    } on DioError catch (e) {
      // TODO: Error handling
      if (e.response != null) {
        // print(e.response.data);
        print(e);
      } else {
        // print(e.request);
        print(e.message);
      }
    }
  }

This code works fine up until print(response). But then the problems begin. Specifically, this is what I see in the console:

I/flutter( 4289): {"records":[{"id":"recrNhzWnPdiSFaCs","createdTime":"2022-07-28T15:45:23.000Z","fields":{"Name":"Cactus ","First":"11.5","App":"The Best App","Current":"98789fg43"}}]}
E/flutter ( 4289): [ERROR:flutter/lib/ui/ui_dart_state.cc(198)] Unhandled Exception: type '_InternalLinkedHashMap<String, dynamic>' is not a subtype of type 'String'
E/flutter(4289): #0 _MainWidgetState.airtableFind(package:example/main.dart:217:50)
E/flutter ( 4289): <asynchronous suspension>

That is I/flutter ( 4289): {"records":[{"id":"recrNhzWnPdiSFaCs","createdTime":"2022-07-28T15:45:23.000Z","fields":{" Name":"Cactus","First":"11.5","App":"The Best App","Current":"98789fg43"}}]} is print(response);.

And then the error Unhandled Exception: type '_InternalLinkedHashMap<String, dynamic>' is not a subtype of type 'String'. How to fix it?

In the future, I need to get data from id, which I will do as follows:

// print(decodedString['records'][0]['id']);
// String id = decodedString['records'][0]['id'];

But at the moment, these lines are commented out, because the error occurs earlier. On the advice of more experienced people, I tried to change final decodedString = json.decode(response.data); to var decodedString = json.decode(response.data.toString()); , but it throws other errors:

I/flutter( 4289): {"records":[{"id":"recrNhzWnPdiSFaCs","createdTime":"2022-07-28T15:45:23.000Z","fields":{"Name":"Cactus ","First":"11.5","App":"The Best App","Current":"98789fg43"}}]}
E/flutter ( 4289): [ERROR:flutter/lib/ui/ui_dart_state.cc(198)] Unhandled Exception: FormatException: Unexpected character (at character 2)
E/flutter(4289): {records: [{id: recrNhzWnPdiSFaCs, createdTime: 2022-07-28T15:45:23.000Z, f...
E/flutter ( 4289): ^
E/flutter ( 4289):
E/flutter ( 4289): #0 _ChunkedJsonParser.fail (dart:convert-patch/convert_patch.dart:1383:5)
E/flutter ( 4289): #1 _ChunkedJsonParser.parse (dart:convert-patch/convert_patch.dart:913:48)
E/flutter ( 4289): #2 _parseJson (dart:convert-patch/convert_patch.dart:35:10)
E/flutter ( 4289): #3 JsonDecoder.convert (dart:convert/json.dart:612:36)
E/flutter ( 4289): #4 JsonCodec.decode (dart:convert/json.dart:216:41)
E/flutter(4289): #5 _MainWidgetState.airtableFind(package:example/main.dart:217:32)
E/flutter ( 4289): <asynchronous suspension>

>Solution :

The problem is that response.data is already decoded from JSON (It’s a Map<String, dynamic>). No need to decode it again with json.decode(response.data);.

Use it like this:

print(response.data['records'][0]['id']);
String id = response.data['records'][0]['id'];

It’s also possible to force response.data to be a String instead of a Map. Just set the responseType option to ResponseType.plain in the Dio.get() like this:

final response = await Dio().get(
  'https://api.airtable.com/v0/'+projectBase+'/'+recordName,
  queryParameters: {'filterByFormula': 'SEARCH('+'"'+testName+'"'+',{Name})'},
  options: Options(
    responseType: ResponseType.plain,   ////////// <- Here
    contentType: 'Application/json',
    headers: {
      'Authorization': 'Bearer'+' '+apiKey,
      'Accept': 'Application/json',
    },
  ),
);