How to parse this JSON Array in Flutter? - arrays

Question

I am working with Flutter and am currently trying to create a graph. I am looking to parse this JSON Array from the link below. My issue is that the information provided in the "prices" object, the values are all inside arrays themselves. I want to get those values and split them into an X and Y list but I have no idea how to accomplish this. I posted a snippet of the JSON data below.
https://api.coingecko.com/api/v3/coins/bitcoin/market_chartvs_currency=usd&days=1
I am only familiar with parsing data by creating a class and constructor. Then create a fromJSON(Map<String, dynamic> json) class and putting the data into a list, as shown in the code snippet below that I created from another URL with object values. How could I go about parsing this array JSON data into two list data?
CODE TO PARSE JSON
List<Coins> _coins = List<Coins>();
Future<List<Coins>> fetchCoins() async {
var url = 'URL';
var response = await http.get(url);
var coins = List<Coins>();
if (response.statusCode == 200) {
var coinsJSON = json.decode(response.body);
for (var coinJSON in coinsJSON) {
coins.add(Coins.fromJson(coinJSON));
}
}
return coins;
}
#override
void initState() {
fetchCoins().then((value) {
setState(() {
_coins.addAll(value);
});
});
super.initState();
}
class Coins{
String symbol;
String name;
Coins(this.symbol, this.name);
Coins.fromJson(Map<String, dynamic> json) {
symbol = json['symbol'];
name = json['name'];
JSON DATA SNIPPET
{
"prices":[
[
1566344769277,
10758.856131083012
],
[
1566345110646,
10747.91694691537
],
[
1566345345922,
10743.789313302059
],
]
}
EDIT: SOLVED WITH THE HELP OF #EJABU.
class HistoricalData {
List prices;
List<num> listX = [];
List<num> listY = [];
HistoricalData(this.prices,this.listX, this.listY);
HistoricalData.fromJson(Map<String, dynamic> json) {
prices = json['prices'];
for (var price in prices) {
listX.add(price[0]);
listY.add(price[1]);
}
}

Answer 1

You may try this...
New class Coins definition:
class Coins {
List<num> listX = [];
List<num> listY = [];
Coins(this.listX, this.listY);
Coins.fromJson(Map<String, dynamic> json) {
List<List<num>> prices = json['prices'];
for (var price in prices) {
listX.add(price[0]);
listY.add(price[1]);
}
}
}
Then later you can fetch it by these lines :
// Future<List<Coins>> fetchCoins() async { // Remove This
Future<Coins> fetchCoins() async {
var url = 'URL';
var response = await http.get(url);
// var coins = List<Coins>(); // Remove This
Coins coins;
if (response.statusCode == 200) {
var coinsJSON = json.decode(response.body);
// Remove This
// for (var coinJSON in coinsJSON) {
// coins.add(Coins.fromJson(coinJSON));
// }
//
coins = Coins.fromJSON(coinsJSON);
}
return coins;
}
Accessing Data in Widget
In Widgets , our expected variable resides as property inside Coins class.
For example, if you use FutureBuilder, you may use these lines:
child: FutureBuilder(
future: fetchCoins(),
builder: (_, __) {
return SomeChartWidget(
listX: coins.listX,
listY: coins.listY,
);
},
),

Answer 2

Generating Serializers automatically
I suggest you take a look at https://pub.dev/packages/json_serializable, which is a package that does the boilerplate code generation for you. Although it might me a bit overkill to add something like this to your code or your workflow, automatically generating serializers is very convenient.
Not that in order to have custom sub-classes, they need to provide serialization as well.
If you want to extend your knowledge even further, you can also have a look at https://pub.dev/packages/built_value and https://pub.dev/packages/built_value_generator