Unhandled Exception: InternalLinkedHashMap<String, dynamic>' is not a subtype of type 'List<dynamic>

I am trying to get the JSON response from the server and output it to the console.

Future<String> login() async {
    var response = await http.get(
        Uri.encodeFull("https://etrans.herokuapp.com/test/2"),
        headers: {"Accept": "application/json"});

    this.setState(() {
      data = json.decode(response.body);
    });


    print(data[0].name);
    return "Success!";
  }

> Unhandled Exception: type '_InternalLinkedHashMap' is > not a subtype of type 'List

What could be the reason?

Here are 2 common ways this could go wrong:

1. If your response is a json array like

   [
       {
         key1: value1,
         key2: value2,
         key3: value3,
       },
       {
         key1: value1,
         key2: value2,
         key3: value3,
       },
   
       .....
   ] 
   

   Then, we use data[0]["name"], not data[0].name Unless we cast to an object that has the name property, we cannot use data[0].name

   We cast like this data = json.decode(response.body).cast<ObjectName>();

   ObjectName can be whatever object you want (Inbuilt or Custom). But make sure it has the name property

2. If your response is a JSON object like

   {
       dataKey: [
         {
           key1: value1,
           key2: value2,
           key3: value3,
         } 
       ] 
   }
   

   Then json.decode will return a Map, not a List

   Map<String, dynamic> map = json.decode(response.body);
   List<dynamic> data = map["dataKey"];
   print(data[0]["name"]);
   

You can use new Map<String, dynamic>.from(snapshot.value);

Easiest way (one dimensional):

Map<String, dynamic> data = new Map<String, dynamic>.from(json.decode(response.body));

print(data['name']);

You are trying to case an Instance of InternalLinkedHashMap which is not possible.

You should Serialize and deserialize it back to Map<String, dynamic>.

InternalLinkedHashMap<String, dynamic> invalidMap;

final validMap =
        json.decode(json.encode(invalidMap)) as Map<String, dynamic>;

You have to convert the runtimeType of data from _InternalLinkedHashMap to an actual List.

One way is to use the List.from.

final _data = List<dynamic>.from(
  data.map<dynamic>(
    (dynamic item) => item,
  ),
);

If you need work with generic fields has a workaround:

class DicData
{
  int tot;
  List<Map<String, dynamic>> fields;

  DicData({
    this.tot,
    this.fields
  });

 factory DicData.fromJson(Map<String, dynamic> parsedJson) {
    return DicData(
        tot: parsedJson['tot'],
        //The magic....
        fields : parsedJson["fields"] = (parsedJson['fields'] as List)
            ?.map((e) => e == null ? null : Map<String, dynamic>.from(e))
            ?.toList()
    );
  }

}

You can get this error if you are using retrofit.dart and declare the wrong return type for your annotated methods:

@GET("/search")
Future<List<SearchResults>> getResults(); 
// wrong! search results contains a List but the actual type returned by that endpoint is SearchResults 

vs

@GET("/search")
Future<SearchResults> getResults(); 
// correct for this endpoint - SearchResults is a composite with field for the list of the actual results

This worked for me:

1. Create a List Data
2. Use Map to decode the JSON file
3. Use the List object Data to fetch the name of the JSON files
4. With the help of index and the list object I have printed the items dynamically from the JSON file

setState(){

    Map<String, dynamic> map = json.decode(response.body);
    Data  = map["name"];
}

// for printing
Data[index]['name1'].toString(),

If your working with Firebase Cloud,make sure that you're not trying to add multiple data with same DocumentID;

firestore.collection('user').document(UNIQUEID).setData(educandos[0].toJson()).

Seems like this error could pop up depending on various developer faults.
In my case, I was using an EasyLocalization key but without defining it under asset/lang/en_US.json file.

I had the same error using json_annotation, json_serializable, build_runner. It occurs when calling the ClassName.fromJson() method for a class that had a class property (example: class User has a property class Address).

As a solution, I modified the generated *.g.dart files of each class, by changing Map<String, dynamic>) to Map<dynamic, dynamic>) in everywhere there is a deep conversion inside the method _$*FromJson

The only problem is that you have to change it again every time you regenerate your files.