Не работает функция onSensorChanged Kotlin

class MainActivity : AppCompatActivity(), SensorEventListener {
    private lateinit var sensorManager: SensorManager
    private lateinit var sensorGravity: Sensor
    private lateinit var button: Button
    private var flag1 = true
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        initViews()
        initSensors()
    }
 
    private fun initViews() {
        button = findViewById(R.id.getLocation)
        button.setOnClickListener {
            if (flag1) {
                registerListener()
                button.text = "Stop"
            } else {
                unregisterListener()
                button.text = "Start"
            }
            flag1 = !flag1
        }
    }
 
    private fun initSensors() {
        sensorManager = getSystemService(Context.SENSOR_SERVICE) as SensorManager
        if (sensorManager.getDefaultSensor(Sensor.TYPE_GRAVITY) != null) {
            sensorGravity = sensorManager.getDefaultSensor(Sensor.TYPE_GRAVITY)
        }
    }
 
    private fun registerListener() {
        if (sensorManager.getDefaultSensor(Sensor.TYPE_GRAVITY) != null) {
            sensorManager.registerListener(this, sensorGravity, SensorManager.SENSOR_DELAY_NORMAL)
        }
    }
 
    private fun unregisterListener() {
        sensorManager.unregisterListener(this, sensorGravity)
    }
 
    override fun onSensorChanged(event: SensorEvent?) {
        println("ok")
    }
 
    override fun onAccuracyChanged(p0: Sensor?, p1: Int) {
        TODO("Not yet implemented")
    }
}