How to implement API data in a line chart - flutter

Question

I am trying to implement my API data in a chart using fl_chart dependencies in flutter. But I just cannot figure out how to implement it.
Here is how I implement my data:
#override
Widget build(BuildContext context) {
return ListView.builder(
padding: EdgeInsets.zero,
shrinkWrap: true,
scrollDirection: Axis.vertical,
physics: NeverScrollableScrollPhysics(),
itemCount: 1,
itemBuilder: (context, index){
// ignore: unused_local_variable
int number = index + 1;
return Container(
width: MediaQuery.of(context).size.width * 0.50,
child: LineChart(
LineChartData(
gridData: FlGridData(
show: true,
drawVerticalLine: true,
getDrawingHorizontalLine: (value) {
return FlLine(
color: const Color(0xff37434d),
strokeWidth: 1,
);
},
getDrawingVerticalLine: (value) {
return FlLine(
color: const Color(0xff37434d),
strokeWidth: 1,
);
},
),
titlesData: FlTitlesData(
show: true,
bottomTitles: SideTitles(
showTitles: true,
reservedSize: 22,
getTextStyles: (value) =>
const TextStyle(color: Color(0xff68737d), fontWeight: FontWeight.bold, fontSize: 16),
getTitles: (value) {
switch (value.toInt()) {
case 2:
return 'MAR';
case 5:
return 'JUN';
case 8:
return 'SEP';
}
return '';
},
margin: 8,
),
leftTitles: SideTitles(
showTitles: true,
getTextStyles: (value) => const TextStyle(
color: Color(0xff67727d),
fontWeight: FontWeight.bold,
fontSize: 15,
),
getTitles: (value) {
switch (value.toInt()) {
case 1:
return '10k';
case 3:
return '30k';
case 5:
return '50k';
}
return '';
},
reservedSize: 28,
margin: 12,
),
),
borderData:
FlBorderData(show: true, border: Border.all(color: const Color(0xff37434d), width: 1)),
minX: 0,
maxX: 11,
minY: 0,
maxY: 6,
lineBarsData: [
LineChartBarData(
spots: [
FlSpot(0 , pings[number.toString()][index].volume),
FlSpot(2.6, 2),
FlSpot(4.9, 5),
FlSpot(6.8, 3.1),
FlSpot(8, 4),
FlSpot(9.5, 3),
FlSpot(11, 4),
],
isCurved: true,
colors: gradientColors,
barWidth: 5,
isStrokeCapRound: true,
dotData: FlDotData(
show: true,
),
belowBarData: BarAreaData(
show: true,
colors: gradientColors.map((color) => color.withOpacity(0.3)).toList(),
),
),
],
)
And here is how i call my data:
Map<String, List<TankPing>> pings;
initState() {
Services.fetchPing().then((tankPings) => {
setState((){
pings = tankPings;
})
});
super.initState();
}
My API call is in another file. I call the API like below:
static Future<Map<String, List<TankPing>>> fetchPing() async {
String url3 = 'https://api.orbital.katsana.com/devices/graph-data';
Future<SharedPreferences> _prefs = SharedPreferences.getInstance();
final SharedPreferences prefs = await _prefs;
final token = prefs.getString('access_token');
final response3 = await http.get(url3, headers: {
'Authorization': 'Bearer $token'
});
if(response3.statusCode == 200) {
final tankPings = tankPingFromJson(response3.body);
return tankPings;
}else if(response3.statusCode == 400) {
print('Connection to server is bad');
}else if(response3.statusCode == 500){
print('No authorization');
}
}
I am trying to implement it inside of FlSPot() function. But then U receive this error:
The method '[]' was called on null.
Receiver: null
Tried calling: []("1")
Here is my model:
import 'dart:convert';
Map<String, List<TankPing>> tankPingFromJson(dynamic str) => Map.from(json.decode(str)).map((k, v) => MapEntry<String, List<TankPing>>(k, List<TankPing>.from(v.map((x) => TankPing.fromJson(x)))));
String tankPingToJson(Map<String, List<TankPing>> data) => json.encode(Map.from(data).map((k, v) => MapEntry<String, dynamic>(k, List<dynamic>.from(v.map((x) => x.toJson())))));
class TankPing {
TankPing({
this.trackedAt,
this.fuel,
this.level,
this.volume,
});
DateTime trackedAt;
double fuel;
double level;
double volume;
factory TankPing.fromJson(Map<String, dynamic> json) => TankPing(
trackedAt: DateTime.parse(json["tracked_at"]),
fuel: json["fuel"].toDouble(),
level: json["level"].toDouble(),
volume: json["volume"].toDouble(),
);
Map<String, dynamic> toJson() => {
"tracked_at": trackedAt.toString(),
"fuel": fuel,
"level": level,
"volume": volume,
};
}
Here is how the API look:
{
"1": [
{
"tracked_at": "2020-11-20T19:41:21.000000Z",
"fuel": 87.03,
"level": 3.0460554,
"volume": 50665.14
},
{
"tracked_at": "2020-11-22T00:19:41.000000Z",
"fuel": 85.75,
"level": 3.0012249,
"volume": 50051.86
},
{
"tracked_at": "2020-11-22T00:32:00.000000Z",
"fuel": 84.17,
"level": 2.9460489,
"volume": 49265.04
},
]
My API is very long and it looks like that. Any help would be appreciated.

Answer 1

I just post the code example in here. If you have any question, you can ask me and I will try to answer the question I can because this code is like almost 2 or 3 years old now and I did not work on this project anymore. Hope the code below helps you!
import 'package:charts_flutter/flutter.dart';
import 'package:flutter/material.dart';
import 'package:provider/provider.dart';
import 'package:charts_flutter/flutter.dart' as charts;
import 'package:intl/intl.dart';
import 'custom_symbol_renderer.dart';
import 'package:orbital_app/Model/tank_ping.dart';
import 'package:orbital_app/Provider/api_provider.dart';
class TankChart extends StatefulWidget {
//This is my API class object to extract the data
TankChart({Key key}) : super(key: key);
#override
_TankChartState createState() => _TankChartState();
}
class _TankChartState extends State<TankChart> {
var ping;
var tankInfo;
// Since I am using a Provider in this code, I call the API here
getPingProvider(){
setState((){
ping = Provider.of<TankPingProvider>(context, listen: false);
ping.getTankPing(context);
});
}
getInfoProvider(){
setState((){
tankInfo = Provider.of<TankInfoProvider>(context, listen: false);
tankInfo.getTankInfo(context);
});
}
#override
initState() {
super.initState();
getPingProvider();
getInfoProvider();
}
#override
Widget build(BuildContext context) {
// Here I format the time to normal human time
final numericFormatter = charts.BasicNumericTickFormatterSpec.fromNumberFormat(
NumberFormat.compact()
);
final ping = Provider.of<TankPingProvider>(context);
return ListView.builder(
padding: EdgeInsets.zero,
// Here I want everything to be shrink and expand when the user needs it
shrinkWrap: true,
// Here is where I set whether the graph can be expand by user vertical
// scroll
physics: NeverScrollableScrollPhysics(),
//The data from the API is here
itemCount: ping.tankPing.length,
itemBuilder: (context, index){
if(ping.tankPing.length == null){
return CircularProgressIndicator();
} else if(ping.tankPing == null){
return CircularProgressIndicator();
} else{
int no = index + 1;
final size = MediaQuery.of(context).size;
// Here is the API dot or data dot on the graph
List<charts.Series<TankPing, DateTime>> series = [
charts.Series(
id: '${tankInfo.tankInfos.data[index].name}',
data: ping.tankPing[no.toString()],
colorFn: (_, __) => MaterialPalette.blue.shadeDefault,
domainFn: (TankPing ping, _) => ping.trackedAt,
measureFn: (TankPing ping, _) => ping.volume
),
];
return Container(
height: 250,
child: Card(
child: Column(
children: [
Expanded(
child: Padding(
padding: const EdgeInsets.only(
left: 5
),
child: charts.TimeSeriesChart(
series,
animate: false,
domainAxis: charts.DateTimeAxisSpec(
tickFormatterSpec: charts.AutoDateTimeTickFormatterSpec(
day: charts.TimeFormatterSpec(
format: 'dd',
transitionFormat: 'dd MMM',
),
),
),
primaryMeasureAxis: charts.NumericAxisSpec(
tickFormatterSpec: numericFormatter,
renderSpec: charts.GridlineRendererSpec(
// Tick and Label styling here.
labelStyle: charts.TextStyleSpec(
fontSize: 10, // size in Pts.
color: charts.MaterialPalette.black
),
)
),
defaultRenderer: charts.LineRendererConfig(
includeArea: true,
includeLine: true,
includePoints: true,
strokeWidthPx: 0.5,
radiusPx: 1.5
),
dateTimeFactory: const charts.LocalDateTimeFactory(),
behaviors: [
charts.SlidingViewport(),
charts.PanAndZoomBehavior(),
charts.SeriesLegend(
position: charts.BehaviorPosition.top,
horizontalFirst: false,
cellPadding: EdgeInsets.only(
left: MediaQuery.of(context).size.width * 0.27,
top: 15
),
),
charts.SelectNearest(
eventTrigger: charts.SelectionTrigger.tap
),
charts.LinePointHighlighter(
symbolRenderer: CustomCircleSymbolRenderer(size: size),
),
],
selectionModels: [
charts.SelectionModelConfig(
type: charts.SelectionModelType.info,
changedListener: (charts.SelectionModel model) {
if(model.hasDatumSelection) {
final tankVolumeValue = model.selectedSeries[0].measureFn(model.selectedDatum[0].index).round();
final dateValue = model.selectedSeries[0].domainFn(model.selectedDatum[0].index);
CustomCircleSymbolRenderer.value = '$dateValue \n $tankVolumeValue L';
}
})
]),
),
),
],
),
),
);
}
});
}
}

Answer 2

The answer is use the min and max value to determine how long the data will be. And then just use the flSpot to enter your data.