Unexpected error while parsing JsonData in flutter - json

Question

Am trying to parse json list data so I could save into an object. But I kept getting errors each time and I do not know why.
Json Data
{
"status": "success",
"data": [
{
"distro_name": "Ikeja Electric (IKEDC)",
"service_id": "ikeja-electric",
"type": [
"prepaid",
"postpaid"
]
},
{
"distro_name": "Eko Electric (EKEDC)",
"service_id": "eko-electric",
"type": [
"prepaid",
"postpaid"
]
},
{
"distro_name": "Ibadan Electric (IBEDC)",
"service_id": "ibadan-electric",
"type": [
"prepaid",
"postpaid"
]
},
{
"distro_name": "Kano Electric (KEDCO)",
"service_id": "kano-electric",
"type": [
"prepaid",
"postpaid"
]
},
{
"distro_name": "Jos Electricity Distribution (JED)",
"service_id": "jos-electric",
"type": [
"prepaid",
"postpaid"
]
},
{
"distro_name": "Port-Harcourt Electric (PHED)",
"service_id": "portharcourt-electric",
"type": [
"prepaid",
"postpaid"
]
}
]
}
This is my model class for the data.
Model
class Providers {
String distro_name;
String service_id;
dynamic type;
Providers(this.distro_name, this.service_id, this.type);
Providers.fromJson(Map<String, dynamic> json):
distro_name = json['distro_name'],
service_id = json['service_id'],
type = json['type'];
}
Main.dart
fetchProviders() async{
try {
final response = await http.get(
uri,
headers: {'Content-Type': 'application/json','Authorization': 'Bearer ' + _bloc.bearerToken, },
);
final responseJson = json.decode(response.body);
for (var u in responseJson["data"]) {
Providers provider = Providers(
u["distro_name"],
u["service_id"],
u["list"]);
providerList.add(provider);
}
return responseJson;
} catch (exception) {
print(exception);
}
}
This is the error I get.
NoSuchMethodError: The method 'add' was called on null.
I/flutter ( 1366): Receiver: null
I don't really know why I get this error. I don't have null values on my api and I have consumed these kind of json structure in the past.

Answer 1

Initialize providerList:
var providerList = </* type */>[]
for (var u in responseJson["data"]) {
Providers provider = Providers(
u["distro_name"],
u["service_id"],
u["list"]);
providerList.add(provider);
}
Using list map:
providerList = responseJson["data"].map((u) => Providers(
u["distro_name"],
u["service_id"],
u["list"],
)).cast<String>().toList();

Answer 2

Model
class Providers {
String distro_name;
String service_id;
dynamic type;
Providers(this.distro_name, this.service_id, this.type);
Providers.fromJson(Map<String, dynamic> json) => Providers(
json['distro_name'],
json['service_id'],
json['type'],
);
}
Main.dart
fetchProviders() async{
try {
final response = await http.get(
uri,
headers: {'Content-Type': 'application/json','Authorization': 'Bearer ' + _bloc.bearerToken, },
);
final responseJson = json.decode(response.body);
responseJson.forEach((data){
Providers provider = Providers.fromJson(data);
providerList.add(provider);
return responseJson;
});
} catch (exception) {
print(exception);
}
}

Answer 3

model
class Providers {
String distro_name;
String service_id;
dynamic type;
Providers(this.distro_name, this.service_id, this.type);
factory Providers.fromJson(Map<String, dynamic> json){
return Providers(
distro_name = json['distro_name'],
service_id = json['service_id'],
type = json['type'],
);
}
}
main.dart
fetchProviders() async{
try {
final response = await http.get(
uri,
headers: {'Content-Type': 'application/json','Authorization': 'Bearer ' + _bloc.bearerToken, },
);
final responseJson = json.decode(response.body);
for (var u in responseJson['data']) {
Providers provider = Providers.fromJson(u);
providerList.add(provider);
return responseJson;
}
}
catch (exception) {
print(exception);
}
}