dart/Flutter: Problems with Decodeing json with utf8 decode - json

Question

I try to load a json-file to put it in a filterable/searchable Listview (search for a diagnosis with a symptom). I'm new to in programming so probably there is a better / simpler way to do this but i would like to do it this way, so it doesnt get more complicated.
I get this error if i try to use utf8.decode:
"The argument type 'String' can't be assigned to the parameter type 'List'."
This is what i tried:
class Services {
static Future<List<User>> getUsers() async {
final response = await rootBundle.loadString('assets/diff.json');
List<User> list = parseUsers(response);
return list;
}
static List<User> parseUsers(String responseBody) {
final parsed = json.decode(utf8.decode(responseBody)).cast<Map<String, dynamic>>();
return parsed.map<User>((json) => User.fromJson(json)).toList();
}
}
the User Class:
class User {
String symptom;
String diagnosis;
User(this.symptom, this.diagnosis);
User.fromJson(Map<String, dynamic> json){
symptom = json['symptom'];
diagnosis = json['diagnosis'];
}
}
extract of the json file:
[
{"symptom":"Kopfschmerz","diagnosis":"Migräne, Spannungskopfschmerz"}
,
{"symptom":"Bauchschmerz","diagnosis":"Apendizitis, Infektion"}
]
Is there a simple way to make this work? Thanks!

Answer 1

With dynamic json.decode(String) the returned object can have a real type of:
List<dynamic>
Map<String, dynamic>
But also when the type is List<dynamic>, decode has parsed also the items in the List, so in your case (since your json has structure [{"" : ""}]) you just need to cast the (reified) List's type parameter with the cast() method.
static List<User> parseUsers(String responseBody) {
//final parsed = json.decode(utf8.decode(responseBody)).cast<Map<String, dynamic>>();
final parsed = (json.decode(responseBody) as List<dynamic>).cast<Map<String, dynamic>>();
return parsed.map<User>((json) => User.fromJson(json)).toList();
}