How to parse dynamic JSON with Flutter? - json

Question

I do not understand how to parse a JSON file I get from firebase.
This is the format of the JSON file
{
"water" : {
"-MnRJkFC3--ZOTmpF1xN" : {
"milliliters" : 0.14,
"time" : "16:26:25"
},
"-MnRJkZRwZYEInHfSKIY" : {
"milliliters" : 48.83,
"time" : "16:26:25"
},
"-MnRJksES18hY765rxxq" : {
"milliliters" : 41.44,
"time" : "16:26:25"
},
"-MnRJlDn6o4RmiGRJS-E" : {
"milliliters" : 11.37,
"time" : "16:26:25"
}
}
}
This is how I am reading the JSON file
Future loadSalesData() async {
final String jsonString = await getJsonFromFirebase();
final dynamic jsonResponse = json.decode(jsonString);
for (Map<String, dynamic> i in jsonResponse)
chartData.add(SalesData.fromJson(i));
}
The getJsonFromFirebase() looks like this:
Future<String> getJsonFromFirebase() async {
String url =
"https://emailpassword. . .seio.com/water.json";
http.Response response = await http.get(Uri.parse(url));
return response.body;
}
When you click on the link it send you to the JSON file which looks like this
{
"-Mnbk2ye2P8bfpaQvNaU": {
"milliliters": 0.0,
"time": "18:07:00"
},
"-Mnbk6wd-wJze8P0JknK": {
"milliliters": 0.12,
"time": "18:07:00"
},
"-Mnbk7Ek629vgBu-MiLg": {
"milliliters": 44.91,
"time": "18:07:00"
},
"-Mnbk7bPuzqwsz9d5nm6": {
"milliliters": 5.43,
"time": "18:07:00"
},
"-Mnbk7v7MADi7YzEbeFI": {
"milliliters": 24.54,
"time": "18:07:00"
},
"-Mnbk8DGfqswckdsA1qP": {
"milliliters": 47.58,
"time": "18:07:00"
},
"-Mnbk8Xw2kJPxLrqCl6h": {
"milliliters": 13.98,
"time": "18:07:00"
}
}
I get the Error
_InternalLinkedHashMap<String, dynamic>' is not a subtype of type 'Iterable'

Answer 1

With the shape of the JSON you are receiving, json.decode will return a Map<String, dynamic> (more specifically an instance of the _InternalLinkedHashMap<String, dynamic> specialisation). This type doesn't implement Iterable, so you can't iterate over it directly with the for-in construct, and this is the exact error you are getting, at run time.
Depending on what you need to construct your SalesData instance, you have two options:
iterate over the entries property, if you need the key of each item ("-Mnbk2ye2P8bfpaQvNaU", "-Mnbk6wd-wJze8P0JknK" etc), otherwise
iterate over the values property, if you don't
Entries
Iteration:
for (MapEntry<String, dynamic> i in jsonResponse.entries) {
chartData.add(SalesData.fromJson(i));
}
SalesData.fromJson:
SalesData.fromJson(MapEntry<String, dynamic> data) {
id = data.key;
milliliters = data.value['milliliters'];
time = data.value['time'];
}
Values
Iteration:
for (Map<String, dynamic> i in jsonResponse.values) {
chartData.add(SalesData.fromJson(i));
}
SalesData.fromJson:
SalesData.fromJson(Map<String, dynamic> data) {
milliliters = data['milliliters'];
time = data['time'];
}
Type Inference
Additionally, regardless of how you decide to iterate over the Map instance, you can clean up the code a little taking advantage of Dart's type inference, so (presuming you are iterating over the entries) loadSalesData could become:
Future loadSalesData() async {
final jsonString = await getJsonFromFirebase();
final jsonResponse = json.decode(jsonString);
for (final i in jsonResponse.entries) {
chartData.add(SalesData.fromJson(i));
}
}
and getJsonFromFirebase could become:
Future<String> getJsonFromFirebase() async {
final url = "http://localhost:8080/data.json";
final response = await http.get(Uri.parse(url));
return response.body;
}

Answer 2

It seems flutter does not understand that jsonResponse is an iterable because you defined it as dynamic.
Adjust the definition to tell flutter it is a map:
final Map<String, dynamic> jsonResponse = json.decode(jsonString);