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<String, dynamic>' is not a subtype of type 'List
What could be the reason?
Here are 2 common ways this could go wrong:
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
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"]);
您可以使用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']);
As doesn't change the type, it's just an assertion.
You need to use:
map['eventType'].cast<String, dynamic>()
or
Map<String, dynamic>.from(map['eventType'])
You can also solved by this way:
Map<String, dynamic> myMap = Map<String, dynamic>.from(/*Your Source*/ );
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:
setState(){
Map<String, dynamic> map = json.decode(response.body);
Data = map["name"];
}
// for printing
Data[index]['name1'].toString(),
如果您使用 Firebase Cloud,请确保您没有尝试添加具有相同 DocumentID 的多个数据;
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.
To convert from _InternalLinkedHashMap<String, dynamic> to Map<String, double> I used
Map<String,double>.from(json['rates'])
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.
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