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Using Sensor Data

This guide explains how to use the Sensor, SensorValue, and their subclasses to access, read, and display live sensor data in your application.

1. Accessing the Sensor Stream

Each sensor provides a stream of live data via the sensorStream property. You can listen to this stream to receive new data as it's emitted:

StreamSubscription? subscription = sensor.sensorStream.listen((value) {
  // Handle the new sensor value
  print("Timestamp: ${value.timestamp}");
  print("Values: ${value.valueStrings}");
});

🔄 Make sure the sensor is properly configured and active before subscribing to the stream. You can learn more about configuring sensors in the Configuring Sensors documentation.

2. Interpreting Sensor Values

The data received from the stream is a subclass of SensorValue. It contains:

  • timestamp: The time the data was recorded.
  • valueStrings: A list of string representations of each axis value (e.g., ["0.1", "0.2", "0.3"]).

You can loop through the values to display or process them:

void handleSensorValue(SensorValue value) {
  for (int i = 0; i < value.dimensions; i++) {
    print("Axis ${i + 1}: ${value.valueStrings[i]}");
  }
}

3. Working with Typed Sensor Values

Depending on the sensor, you may receive:

  • SensorDoubleValue — contains List<double> values
  • SensorIntValue — contains List<int> values

To access the raw numeric data:

sensor.sensorStream.listen((value) {
  if (value is SensorDoubleValue) {
    print("Double values: ${value.values}");
  } else if (value is SensorIntValue) {
    print("Int values: ${value.values}");
  }
});

4. Understanding Axis Metadata

You can use the sensor’s axisNames and axisUnits to label or format values meaningfully:

for (int i = 0; i < sensor.axisCount; i++) {
  print("${sensor.axisNames[i]} (${sensor.axisUnits[i]}): ${value.valueStrings[i]}");
}

5. Timestamp Handling

Each SensorValue includes a timestamp which represents the time the reading was taken. The time unit is determined by the sensor’s timestampExponent.

Example:

  • -3 means the timestamp is in milliseconds
  • 0 means seconds
  • -6 means microseconds

To convert the timestamp to a DateTime (assuming the timestamp is in milliseconds):

DateTime timestamp = DateTime.fromMillisecondsSinceEpoch(value.timestamp);

Adjust accordingly based on timestampExponent.

6. Best Practices

  • Always check the sensor is configured and enabled before using the stream.
  • Unsubscribe from the stream when the data is no longer needed:
subscription?.cancel();
  • Use valueStrings for display and values for numeric computation (when using typed values).

This guide covers the typical usage of sensor data in your app. Make sure to refer to your specific sensor subclass for any additional functionality or interpretation.