How to start receiver, getting "lateinit property notificationManager has not been initialized" - kotlin

Question

I am trying to make an alarm that sends notification when application is closed. I created an Alarm Manager in the MainActivity and created an inner class for the BroadcastReceiver as soon as the onReceive() is triggered, I need to send a notification. The alarm works but each time it tries to send the notification, I get an error of
2020-03-25 13:19:33.166 15045-15045/com.kotlin.ambulantlcs
E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.kotlin.ambulantlcs, PID: 15045
java.lang.RuntimeException: Unable to start receiver com.kotlin.ambulantlcs.ui.MainActivity$Receiver:
kotlin.UninitializedPropertyAccessException: lateinit property
notificationManager has not been initialized
at android.app.ActivityThread.handleReceiver(ActivityThread.java:3997)
at android.app.ActivityThread.access$1500(ActivityThread.java:267)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1992)
at android.os.Handler.dispatchMessage(Handler.java:107)
at android.os.Looper.loop(Looper.java:237)
at android.app.ActivityThread.main(ActivityThread.java:7777)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1047)
Caused by: kotlin.UninitializedPropertyAccessException: lateinit property notificationManager has not been initialized
at com.kotlin.ambulantlcs.ui.MainActivity$Receiver.onReceive(MainActivity.kt:100)
at android.app.ActivityThread.handleReceiver(ActivityThread.java:3988)
at android.app.ActivityThread.access$1500(ActivityThread.java:267) 
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1992) 
at android.os.Handler.dispatchMessage(Handler.java:107) 
at android.os.Looper.loop(Looper.java:237) 
at android.app.ActivityThread.main(ActivityThread.java:7777) 
at java.lang.reflect.Method.invoke(Native Method) 
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493) 
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1047)
See my whole code below:
import android.app.*
import android.content.BroadcastReceiver
import android.content.Context
import android.content.Intent
import android.graphics.Color
import android.os.Build
import android.os.Bundle
import android.util.Log
import android.widget.RemoteViews
import android.widget.Toast
import androidx.appcompat.app.AppCompatActivity
import androidx.navigation.NavOptions
import androidx.navigation.Navigation
import androidx.navigation.ui.AppBarConfiguration
import androidx.navigation.ui.NavigationUI
import com.kotlin.ambulantlcs.R
import com.kotlin.ambulantlcs.storage.SharedDataManager
import com.kotlin.ambulantlcs.ui.fragments.LoginFragmentDirections
import java.util.*
open class MainActivity : AppCompatActivity() {
lateinit var context: Context
lateinit var alarmManager: AlarmManager
val obj: MainActivity = this
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
val appBarConfiguration = AppBarConfiguration
.Builder(R.id.homeFragment, R.id.loginFragment)
.build()
setAlarm()
if(SharedDataManager.getInstance(this).isLoggedIn) {
var navOptions = NavOptions.Builder()
.setPopUpTo(R.id.action_login_Home, true)
.build()
val navController = Navigation.findNavController(this, R.id.fragment)
NavigationUI.setupActionBarWithNavController(this, navController, appBarConfiguration)
navController.navigate(
LoginFragmentDirections.actionLoginHome()
)
} else {
val navController = Navigation.findNavController(this, R.id.fragment )
NavigationUI.setupActionBarWithNavController(this, navController, appBarConfiguration)
}
}
override fun onBackPressed() {
Toast.makeText(applicationContext, "Function is not allowed", Toast.LENGTH_SHORT).show()
}
override fun onSupportNavigateUp(): Boolean {
return NavigationUI.navigateUp(Navigation.findNavController(this, R.id.fragment), null)
}
fun setAlarm() {
Log.d("MainActivity", "Create: ${Date().toString()}")
context = this
alarmManager = getSystemService(Context.ALARM_SERVICE) as AlarmManager
val seconds = 10 * 1000
val intent = Intent(context, Receiver::class.java)
val pendingIntent = PendingIntent.getBroadcast(context, 0, intent, PendingIntent.FLAG_UPDATE_CURRENT)
Log.d("MainActivity", "SECONDS: ${seconds.toLong()}")
alarmManager.setRepeating(AlarmManager.RTC_WAKEUP, seconds.toLong(), seconds.toLong(), pendingIntent)
}
class Receiver : BroadcastReceiver() {
lateinit var notificationManager : NotificationManager
lateinit var notificationChannel : NotificationChannel
lateinit var builder : Notification.Builder
private val channelId = "i.apps.notifications"
private val description = "Test notification"
override fun onReceive(context: Context?, intent: Intent?) {
Log.d("MainActivity", " Receiver: ${Date().toString()}")
val intent = Intent(context, MainActivity::class.java)
val pIntent = PendingIntent.getActivity(context, 0, intent, PendingIntent.FLAG_UPDATE_CURRENT)
val contentView = RemoteViews("com.kotlin.ambulantlcs",
R.layout.activity_main)
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
notificationChannel = NotificationChannel(
channelId,description,NotificationManager.IMPORTANCE_HIGH)
notificationChannel.enableLights(true)
notificationChannel.lightColor = Color.GREEN
notificationChannel.enableVibration(false)
notificationManager.createNotificationChannel(notificationChannel)
builder = Notification.Builder(context, channelId)
.setContent(contentView)
.setSmallIcon(R.drawable.ic_launcher_background)
.setContentIntent(pIntent)
}else{
builder = Notification.Builder(context)
.setContent(contentView)
.setSmallIcon(R.drawable.ic_launcher_background)
.setContentIntent(pIntent)
}
notificationManager.notify(1234,builder.build())
}
}
}
How can I correct this?

Answer 1

Your notificationManger is null (you dont initialize him). Try this:
if (notificationManager == null) {
notificationManager = (NotificationManager) getSystemService(Context.NOTIFICATION_SERVICE);
}

Answer 2

The reason the app crashes is that you don't initialize notificationManager. Instead of declaring it as lateinit var you could just initialize it in your Receiver class:
val notificationManager : NotificationManager = getSystemService(Context.NOTIFICATION_SERVICE)