Android ProcessLifecycleOwner 
by example - source code for article https://alexzh.com/2019/08/19/android-processlifecycleowner-by-example/

Analytics.kt

class Analytics {
    private var startSessionTimestamp: Long = -1
    private val reporters = mutableListOf<AnalyticsReporter>()

    fun addReporter(reporter: AnalyticsReporter) {
        reporters.add(reporter)
    }

    fun startSession() {
        startSessionTimestamp = Date().time
    }

    fun stopSession() {
        reportSession()
        sendAllEvents()
        startSessionTimestamp = -1
    }

    private fun reportSession() {
        reporters.forEach {reporter ->
        val currentTime = Date().time
        // we should check if session was started and stopped correctly
        val sessionTime = (currentTime - startSessionTimestamp) / 1000
            reporter.report("Session time: $sessionTime sec" )
        }
    }

    private fun sendAllEvents() {
        reporters.forEach {reporter ->
            reporter.sendAllEvents()
        }
    }
}

AnalyticsReporter.kt

interface AnalyticsReporter {

    fun report(event: String)

    fun sendAllEvents()
}

ApplicationObserver.kt

class ApplicationObserver(val analytics: Analytics) : LifecycleObserver {

    @OnLifecycleEvent(Lifecycle.Event.ON_START)
    fun onForeground() {
        analytics.startSession()
    }

    @OnLifecycleEvent(Lifecycle.Event.ON_STOP)
    fun onBackground() {
        analytics.stopSession()
    }
}

build.gradle

    dependencies {
        ...
        implementation "androidx.lifecycle:lifecycle-runtime:2.0.0"
        implementation "androidx.lifecycle:lifecycle-extensions:2.0.0"
        annotationProcessor "androidx.lifecycle:lifecycle-compiler:2.0.0"
    }

LogReporter.kt

class LogReporter : AnalyticsReporter {
    private val events = mutableListOf<String>()

    override fun report(event: String) {
        events.add(event)
    }

    override fun sendAllEvents() {
        events.forEach { event ->
            Log.d(this.javaClass.simpleName, event)
        }
        events.clear()
    }
}

MapNotesApp.kt

class MapNotesApp : Application() {
    override fun onCreate() {
        super.onCreate()
        ...

        val analytics = Analytics()
        analytics.addReporter(LogReporter())

        ProcessLifecycleOwner
                .get()
                .lifecycle
                .addObserver(ApplicationObserver(analytics))
    }
    ...
}