Where to call setState to update graph - flutter

Question

I'm struggling to get a graph widget to rebuild when the underlying data is changed. I have tried setState in a few different spots and can't figure it out.
Any ideas?
Data is stored in class:
class SensorReading {
SensorReading({
required this.timestamp,
required this.value,
});
DateTime timestamp;
double value;
}
class Sensor {
Sensor({
});
List<SensorReading> readings = [];
}
I'm listening to some data coming in from bluetooth and adding readings.
await c.setNotifyValue(true);
c.value.listen((value) {
setState(() {
sensor.readings.add(SensorReading(timestamp: DateTime.now(), value: value));
}
}
The main widget contains a graph widget. The graph widget will only update when I force a redraw by rotating the screen or similar.
#override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text('Sensor readings'),
),
body: Column(
children: <Widget>[
Expanded(
flex: 1,
child: SfCartesianChart(
primaryXAxis: CategoryAxis(),
// Chart title
title: ChartTitle(text: 'Live stream'),
// Enable legend
legend: Legend(isVisible: true),
// Enable tooltip
tooltipBehavior: TooltipBehavior(enable: false),
series: <ChartSeries<SensorReading, DateTime>>[
LineSeries<SensorReading, DateTime>(
dataSource: widget.sensor.readings,
xValueMapper: (SensorReading reading, _) => reading.timestamp,
yValueMapper: (SensorReading reading, _) => reading.value,
name: 'Temp',
// Enable data label
dataLabelSettings: DataLabelSettings(isVisible: false))
]),
),
]
)
}