TL;DR how can I have an Android sensor permanently running/active/registered for my app, even if I close it?
Objective:
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:
myStepCount to increment by 1.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.Important:
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...
Observations:
TYPE_STEP_COUNTER sensor is permanently registered).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.Conclusion:
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() {
WidgetsFlutterBinding.ensureInitialized();
runApp(App());
}
class App extends StatefulWidget {
@override
_AppState createState() => _AppState();
}
class _AppState extends State<App> with WidgetsBindingObserver {
@override
void initState() {
super.initState();
if (Platform.isAndroid) {
_activateStepCounterSensor();
} 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');
break;
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)
break;
default:
print('_activateStepCounterSensor(): unknown result: $result');
break;
}
}
//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) {
super.configureFlutterEngine(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" -> {
activateStepCounterSensor(result)
}
}
}
}
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
result.success("success")
}
}
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.
Update: 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).
I have so many people asking me for a more detailed description of how I solved my problem. Unfortunately I can't share my whole code with you, just this small snipped which always gets run at the beginning (right after main()):
if (Platform.isAndroid && !SharedPrefsHelper().isForegroundServiceStarted()) {
ForegroundService().start();
// ForegroundServiceNotification.setPriority(AndroidNotificationPriority.LOW);
SharedPrefsHelper().setIsForegroundServiceStarted(true);
}
Don't worry about SharedPrefsHelper, that's just a class that I created to make it easier to work with shared_preferences.