Flutter: how can I permanently register a sensor (and never unregister it?)


TL;DR how can I have an Android sensor permanently running/active/registered for my app, even if I close it?

I’m making a Flutter application that counts your steps using the pedometer package,
which uses the built-in sensor TYPE_STEP_COUNTER of Android,
which returns the # of steps taken since last boot (iOS). On Android, any steps taken before installing the app are not counted.

How I implemented it:

  • When the app is actively running in the foreground, each step causes
    a myStepCount to increment by 1.
  • In all other cases (phone locked, went to home-screen, closed the app…), the android TYPE_STEP_COUNTER sensor should
    still be running
    in the background, and once I open my app again, the
    difference between new stepCount and last saved stepCount (saved
    using shared_prefs) will be calculated and added to myStepCount.

The TYPE_STEP_COUNTER sensor must be permanently running/stay registered in the background, even after I lock my phone, go to the home-screen, or close the app…


  • On my Samsung Galaxy A02s, my app works perfectly fine, as it it supposed to
    (as described above). That is because on that phone I also have the
    Google Fit app installed, which tracks your steps 24/7 (so the
    TYPE_STEP_COUNTER sensor is permanently registered).
  • On my Samsung Galaxy S7, my app does not work as it’s supposed to.
    myStepCount gets incremented when I take steps while the app is
    running in the foreground. But steps taken while the app is closed
    will NOT be added to myStepCount once I open the app again.
    Note: I don’t have any other step-counting-apps like Google Fit on this phone.

I need to find a way to register the TYPE_STEP_COUNTER sensor from my Flutter app, and keep it registered even after I close the app.

2 Attempted (but unsuccessful) Solutions:

1st Attempt:
Calling Native Android Code from my Flutter Code to register the sensor
This is my main.dart file (with the unimportant parts left out for simplicity):

void main() {

class App extends StatefulWidget {
  _AppState createState() => _AppState();

class _AppState extends State<App> with WidgetsBindingObserver {

  void initState() {

    if (Platform.isAndroid) {
    } else if (Platform.isIOS) {
      //TODO check if anything is needed to to here

  void _activateStepCounterSensor() async {
    MethodChannel _stepCounterChannel = MethodChannel('com.cedricds.wanderapp/stepCounter'); //convention
    dynamic result = await _stepCounterChannel.invokeMethod('activateStepCounterSensor');
    switch (result) {
      case "success":
        //The following line gets printed when I run the flutter app on my Samsung Galaxy S7:
        print('_activateStepCounterSensor(): successfully registered step counter sensor for android');
      case "error":
        print('_activateStepCounterSensor(): failed to register step counter sensor (not available) for android');
        //TODO display errorpage (because app is completely useless in this case)
        print('_activateStepCounterSensor(): unknown result: $result');

  //build() and other lifecycle-methods and helper methods: not important for this question

This is my MainActivity.kt file:

package com.cedricds.wanderapp

import android.content.Context
import android.hardware.Sensor
import android.hardware.SensorEvent
import android.hardware.SensorEventListener
import android.hardware.SensorManager
import android.util.Log
import android.widget.Toast
import io.flutter.embedding.android.FlutterActivity
import io.flutter.embedding.engine.FlutterEngine
import io.flutter.plugin.common.MethodChannel

class MainActivity2: FlutterActivity(), SensorEventListener {

    private val STEP_COUNTER_CHANNEL = "com.cedricds.wanderapp/stepCounter";
    private lateinit var channel: MethodChannel

    override fun configureFlutterEngine(flutterEngine: FlutterEngine) {

        channel = MethodChannel(flutterEngine.dartExecutor.binaryMessenger, STEP_COUNTER_CHANNEL)
        channel.setMethodCallHandler { call, result ->
            when(call.method){ //this is like switch-case statement in Java
                "activateStepCounterSensor" -> {

    private var sensorManager : SensorManager?=null
    private var sensor: Sensor ?= null

    private fun activateStepCounterSensor(result: MethodChannel.Result) {
        //This line gets printed when I run the flutter app, so the method gets called successfully:
        Log.d("Android", "Native Android: activateStepCounterSensor()")
        sensorManager = getSystemService(Context.SENSOR_SERVICE) as SensorManager
        sensor = sensorManager?.getDefaultSensor(Sensor.TYPE_STEP_COUNTER)
        if (sensor == null) {
            Toast.makeText(this, "missing hardware.", Toast.LENGTH_LONG).show()
            result.error("error", "error", "error")
        } else {
            sensorManager?.registerListener(this, sensor, SensorManager.SENSOR_DELAY_NORMAL)
            //This line gets printed:
            Log.d("Android", "Native Android: registered TYPE_STEP_COUNTER")
            //and never unregister that listener

    override fun onSensorChanged(p0: SensorEvent?) {}
    override fun onAccuracyChanged(p0: Sensor?, p1: Int) {}

Despite the few print(...) and Log.d(...) being printed in the console as expected, the app doesn’t work how I expected it to work. When I exit the app, walk for example 50 steps, then open the app again, those 50 steps are missing. It seems the sensor is being unregistered somewhere.

2nd Attempt:
Modifying the pedometer package’s code by removing unregisterListener(...):
The only changes I did to the file were 2 Log.d(...) statements and more importantly, commenting out a specific line of code.

modified SensorStreamHandler.kt from the pedometer package:

package com.example.pedometer

import android.content.Context
import android.hardware.Sensor
import android.hardware.SensorEventListener
import android.hardware.SensorManager
import android.os.Looper
import io.flutter.embedding.engine.plugins.FlutterPlugin
import io.flutter.plugin.common.BinaryMessenger
import io.flutter.plugin.common.EventChannel
import android.os.Handler
import android.util.Log

class SensorStreamHandler() : EventChannel.StreamHandler {

    private var sensorEventListener: SensorEventListener? = null
    private var sensorManager: SensorManager? = null
    private var sensor: Sensor? = null
    private lateinit var context: Context
    private lateinit var sensorName: String
    private lateinit var flutterPluginBinding: FlutterPlugin.FlutterPluginBinding

    constructor(flutterPluginBinding: FlutterPlugin.FlutterPluginBinding, sensorType: Int) : this() {
        this.context = flutterPluginBinding.applicationContext
        this.sensorName = if (sensorType == Sensor.TYPE_STEP_COUNTER) "StepCount" else "StepDetection"
        sensorManager = context.getSystemService(Context.SENSOR_SERVICE) as SensorManager
        sensor = sensorManager!!.getDefaultSensor(sensorType)
        this.flutterPluginBinding = flutterPluginBinding

    override fun onListen(arguments: Any?, events: EventChannel.EventSink?) {
        Log.d("Pedometer", "Native Android: onListen()")
        if (sensor == null) {
            events!!.error("1", "$sensorName not available",
                    "$sensorName is not available on this device");
        } else {
            sensorEventListener = sensorEventListener(events!!);
            sensorManager!!.registerListener(sensorEventListener, sensor, SensorManager.SENSOR_DELAY_NORMAL);

    override fun onCancel(arguments: Any?) {
        Log.d("Pedometer", "Native Android: onCancel()")
        //The only change I did: commenting out the following line:
//        sensorManager!!.unregisterListener(sensorEventListener);


This also did not solve my problem. So if someone knows how I can permanently register the TYPE_STEP_COUNTER sensor in my flutter app, please let me know.


I’ve contacted one of the developers of the pedometer package, and he suggested me to use flutter_foreground_service (which is developed by the same team/company as pedometer). It works.

But I would still find it interesting, if there is another way (maybe similar to my 2 failed attempts).

Answered By – Cedric

Answer Checked By – Timothy Miller (FlutterFixes Admin)

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