Только допустимые (?.) Или ненулевые утвержденные (!!.) Вызовы разрешены для обнуляемого получателя типа SensorEvent?

Question

Я пытаюсь создать приложение для компаса в Android studio kotlin ... вот код

class MainActivity : AppCompatActivity() , LocationListener, SensorEventListener{

val REQUEST_LOCATION = 2

private var sensorManager: SensorManager ?= null

override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    setContentView(R.layout.activity_main)
    setLocation()

    sensorManager - getSystemService(Context.SENSOR_SERVICE) as SensorManager
    startCompass()
}

private fun setLocation() {
    if (ActivityCompat.checkSelfPermission(this, Manifest.permission.ACCESS_FINE_LOCATION)
        != PackageManager.PERMISSION_GRANTED
        && ActivityCompat.checkSelfPermission(this,Manifest.permission.ACCESS_COARSE_LOCATION)
    != PackageManager.PERMISSION_GRANTED) {
        ActivityCompat.requestPermissions(this, arrayOf(Manifest.permission.ACCESS_FINE_LOCATION, Manifest.permission.ACCESS_COARSE_LOCATION),
            REQUEST_LOCATION)
    }else{
        val locationManager = getSystemService(Context.LOCATION_SERVICE) as LocationManager
        val criteria = Criteria()
        val provider = locationManager.getBestProvider(criteria, false)
        val location = locationManager.getLastKnownLocation(provider)

        locationManager.requestLocationUpdates(LocationManager.GPS_PROVIDER, 1000, 0f, this)
        if (location != null)
        {
            text_view_location.text = convertLocationToString(location.latitude, location.longitude)
        } else {
            Toast.makeText(this, "GPS non disponibile", Toast.LENGTH_SHORT).show()
        }
    }

}

override fun onRequestPermissionsResult(requestCode: Int, permissions: Array<out String>, grantResults: IntArray) {
    if (requestCode == REQUEST_LOCATION) setLocation()
}

private fun convertLocationToString(latitude: Double, longitude: Double): String {

    val builder = StringBuilder()
    if (latitude < 0) builder.append("S ") else builder.append("N ")

    val latitudeDegrees = Location.convert(Math.abs(latitude), Location.FORMAT_SECONDS)
    val latitudeSplit =latitudeDegrees.split((":").toRegex()).dropLastWhile({it.isEmpty()}).toTypedArray()
    builder.append(latitudeSplit[0])
    builder.append("°")
    builder.append(latitudeSplit[1])
    builder.append("'")
    builder.append(latitudeSplit[2])
    builder.append("\"")
    builder.append("\n")

    if (longitude < 0) builder.append("W ") else builder.append("E ")

    val longitudeDegrees = Location.convert(Math.abs(longitude), Location.FORMAT_SECONDS)
    val longitudeSplit =longitudeDegrees.split((":").toRegex()).dropLastWhile({it.isEmpty()}).toTypedArray()
    builder.append(longitudeSplit[0])
    builder.append("°")
    builder.append(longitudeSplit[1])
    builder.append("'")
    builder.append(longitudeSplit[2])
    builder.append("\"")

    return builder.toString()
}

override fun onLocationChanged(location: Location?) {
    setLocation()
}

override fun onStatusChanged(provider: String?, status: Int, extras: Bundle?) {

}

override fun onProviderEnabled(p0: String?) {

}

override fun onProviderDisabled(p0: String?) {

}

override fun onAccuracyChanged(p0: Sensor, p1: Int) {
    TODO("not implemented") //To change body of created functions use File | Settings | File Templates.
}

private var rotationMatrix = FloatArray(9)

private var orientation = FloatArray(3)

private var azimuth: Int = 0

private var lastAccelerometer = FloatArray(3)

private var lastAccelerometerSet = false

private var lastMagnetometer = FloatArray(3)

private var lastMagnetometerSet = false

override fun onSensorChanged(event: SensorEvent?) {
    if (event.sensor.type == Sensor.TYPE_ROTATION_VECTOR){
        SensorManager.getRotationMatrix(rotationMatrix,event.values)
        azimuth = (Math.toDegrees(SensorManager.getOrientation(rotationMatrix, orientation)[0].toDouble())+360).toInt()%360
    }

    if (event.sensor.type == Sensor.TYPE_ACCELEROMETER){
        System.arraycopy(event.values,0,lastAccelerometer,0,event.values.size)
        lastAccelerometerSet = true
    } else if (event.sensor.type == Sensor.TYPE_MAGNETIC_FIELD) {
        System.arraycopy(event.values, 0, lastMagnetometer, 0, event.values.size)
        lastMagnetometerSet = true
    }

    if(lastAccelerometerSet && lastMagnetometerSet){
        SensorManager.getRotationMatrix(rotationMatrix, null,lastAccelerometer,lastMagnetometer)
        SensorManager.getOrientation(rotationMatrix, orientation)
        azimuth = (Math.toDegrees(SensorManager.getOrientation(rotationMatrix,orientation)[0].toDouble())+360).toInt()%360
    }

    azimuth = Math.round(azimuth.toFloat())
    compass_image.rotation = (-azimuth).toFloat()

    val where = when(azimuth){
        in 281..348 -> "NW"
        in 281..348 -> "NW"
        in 281..348 -> "NW"
        in 281..348 -> "NW"
        in 281..348 -> "NW"
        in 281..348 -> "NW"
        in 281..348 -> "NW"
        else -> "N"
    }

    view_degree.text = "$azimuth° $where"
}

private var accelerometer: Sensor? = null

private var magnetometer: Sensor? = null

private var haveSensorAccelerometer = false

private var haveSensorMagnetometer = false

private var rotationVector: Sensor? = null

private var haveSensorRotationVector = false

private fun startCompass(){
    if (sensorManager!!.getDefaultSensor(Sensor.TYPE_ROTATION_VECTOR)==null){
        if (sensorManager!!.getDefaultSensor(Sensor.TYPE_ACCELEROMETER)==null || sensorManager!!.getDefaultSensor(Sensor.TYPE_MAGNETIC_FIELD) == null){
            noSensorAlert()
        } else {
            accelerometer = sensorManager!!.getDefaultSensor(Sensor.TYPE_ACCELEROMETER)
            magnetometer = sensorManager!!.getDefaultSensor(Sensor.TYPE_MAGNETIC_FIELD)

            haveSensorAccelerometer = sensorManager!!.registerListener(this,accelerometer,SensorManager.SENSOR_DELAY_UI)
            haveSensorMagnetometer = sensorManager!!.registerListener(this,magnetometer,SensorManager.SENSOR_DELAY_UI)
        }
    } else {
            rotationVector = sensorManager!!.getDefaultSensor(Sensor.TYPE_ROTATION_VECTOR)
            haveSensorRotationVector = sensorManager!!.registerListener(
                this,
                rotationVector,
                SensorManager.SENSOR_DELAY_UI
            )
    }

}
private fun stopCompass(){
    if (haveSensorRotationVector) sensorManager!!.unregisterListener(this,rotationVector)
    if (haveSensorAccelerometer) sensorManager!!.unregisterListener(this,accelerometer)
    if (haveSensorMagnetometer) sensorManager!!.unregisterListener(this,magnetometer)
}

private fun noSensorAlert() {
    val alertDialog = AlertDialog.Builder(this)
    alertDialog.setMessage("Il tuo dispositivo non supporta la bussola!")
        .setCancelable(false)
        .setNegativeButton("Close"){_,_ -> finish()}
    alertDialog.show()
}

override fun onResume() {
    super.onResume()
    startCompass()
}

override fun onPause(){
    super.onPause()
    stopCompass()
}

}

но каждый раз, когда я пытаюсь создать приложение «event.sensor» показывает ошибку «Только безопасные (?.) или ненулевые утвержденные (!!.) вызовы разрешены для обнуляемого получателя типа SensorEvent?» Как я могу это исправить? Вы можете помочь мне? Я не знаю, почему он появляется и когда я использую сейф "?" это показывает гораздо больше ошибок, чем сейчас! Заранее спасибо.