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java.lang.IllegalStateException: 'awaitClose { yourCallbackOrListener.cancel() }' should be used in the end of callbackFlow block

I am getting an error the first time the user sign in, however, there is no error the second time the user open the app
from the logcat the awaiClose function is triggered. so where is the error come from?!
The code
val userIdFlow = callbackFlow {
val listener = FirebaseAuth.AuthStateListener { firebaseAuth ->
Timber.tag("Auth_Util").d("Changed")
firebaseAuth.currentUser?.let {
Timber.tag("Auth_Util").d("user exist, id = ${it.uid}")
trySend(it.uid) // the line mentioned in the error message (AuthUtil.kt:38)
}
}
auth.addAuthStateListener(listener)
awaitClose {
Timber.tag("Auth_Util").d("Closed")
auth.removeAuthStateListener(listener)
}
}
The Logcat
2022-10-13 16:00:11.541 6972-6972 Auth_Util com.hussienFahmy.myGpaManager D Changed
2022-10-13 16:00:11.541 6972-6972 Auth_Util com.hussienFahmy.myGpaManager D user exist, id = g11Hbz2EUWXGSE0WnbcF2nJRUPQ2
2022-10-13 16:00:11.543 6972-6972 Auth_Util com.hussienFahmy.myGpaManager D Closed
2022-10-13 16:00:11.716 6972-6972 AndroidRuntime com.hussienFahmy.myGpaManager E FATAL EXCEPTION: main
Process: com.hussienFahmy.myGpaManager, PID: 6972
java.lang.IllegalStateException: 'awaitClose { yourCallbackOrListener.cancel() }' should be used in the end of callbackFlow block.
Otherwise, a callback/listener may leak in case of external cancellation.
See callbackFlow API documentation for the details.
at kotlinx.coroutines.flow.CallbackFlowBuilder.collectTo(Builders.kt:343)
at kotlinx.coroutines.flow.internal.ChannelFlow$collectToFun$1.invokeSuspend(ChannelFlow.kt:60)
at kotlin.coroutines.jvm.internal.BaseContinuationImpl.resumeWith(ContinuationImpl.kt:33)
at kotlinx.coroutines.DispatchedTask.run(DispatchedTask.kt:106)
at kotlinx.coroutines.EventLoop.processUnconfinedEvent(EventLoop.common.kt:69)
at kotlinx.coroutines.DispatchedTaskKt.resumeUnconfined(DispatchedTask.kt:245)
at kotlinx.coroutines.DispatchedTaskKt.dispatch(DispatchedTask.kt:161)
at kotlinx.coroutines.CancellableContinuationImpl.dispatchResume(CancellableContinuationImpl.kt:397)
at kotlinx.coroutines.CancellableContinuationImpl.completeResume(CancellableContinuationImpl.kt:513)
at kotlinx.coroutines.channels.AbstractChannel$ReceiveElement.completeResumeReceive(AbstractChannel.kt:908)
at kotlinx.coroutines.channels.ArrayChannel.offerInternal(ArrayChannel.kt:83)
at kotlinx.coroutines.channels.AbstractSendChannel.trySend-JP2dKIU(AbstractChannel.kt:155)
at kotlinx.coroutines.channels.ChannelCoroutine.trySend-JP2dKIU(Unknown Source:2)
at com.hussienFahmy.myGpaManager.network.AuthUtil$userIdFlow$1.invokeSuspend$lambda-1(AuthUtil.kt:38)
at com.hussienFahmy.myGpaManager.network.AuthUtil$userIdFlow$1.$r8$lambda$gz_nO4N2PXNldWwFNxezrd-NGHg(Unknown Source:0)
at com.hussienFahmy.myGpaManager.network.AuthUtil$userIdFlow$1$$ExternalSyntheticLambda0.onAuthStateChanged(Unknown Source:2)
at com.google.firebase.auth.zzk.run(com.google.firebase:firebase-auth##21.0.8:1)
at android.os.Handler.handleCallback(Handler.java:938)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:236)
at android.app.ActivityThread.main(ActivityThread.java:8057)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:620)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1011)
Suppressed: kotlinx.coroutines.DiagnosticCoroutineContextException: [StandaloneCoroutine{Cancelling}#1daddb6, Dispatchers.Main.immediate]

App restarts when resuming from background after some time

The scenario is when the app is on Fragment A and then kept the app in the background for some time. After resuming from the background the initial state of the app is in Fragment A but then suddenly app restarts from startDestination in the navigation component causing the below crash.
Fatal Exception: java.lang.IllegalArgumentException: Navigation action/destination com.app.gulfcraftv2:id/action_splashFragment_to_nav_home cannot be found from the current destination Destination(com.app.gulfcraftv2:id/companyFragment) class=com.precise.gulfcraft.ui.companydetail.CompanyDetailFragment
at androidx.navigation.NavController.navigate(NavController.kt:1540)
at androidx.navigation.NavController.navigate(NavController.kt:1472)
at androidx.navigation.NavController.navigate(NavController.kt:1930)
at com.precise.gulfcraft.ui.splash.SplashFragment.onCreate$lambda-6(SplashFragment.kt:75)
at com.precise.gulfcraft.ui.splash.SplashFragment.lambda$Aso8YI02DbFhfWptH-qrBUU0ulU()
at com.precise.gulfcraft.ui.splash.-$$Lambda$SplashFragment$Aso8YI02DbFhfWptH-qrBUU0ulU.run(:2)
at android.os.Handler.handleCallback(Handler.java:883)
at android.os.Handler.dispatchMessage(Handler.java:100)
at android.os.Looper.loop(Looper.java:224)
at android.app.ActivityThread.main(ActivityThread.java:7562)
at java.lang.reflect.Method.invoke(Method.java)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:539)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:950)
Note - The launch mode used is singleTop
The crash is happening in the below section.
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
try {
Handler(Looper.getMainLooper()).postDelayed({
findNavController().navigate(SplashFragmentDirections.actionSplashFragmentToNavHome())
}, 3000)
} catch (e: Exception) {
}
}

check first if this is your current destination with following function
fun navigate(destination: NavDirections) = with(findNavController()) {
currentDestination?.getAction(destination.actionId)
?.let { navigate(destination) }
}

Why The App Crashed After Processed a Command Using a setOnClickListener?

So I am using firebase to upload my data by filling a form and sending a cover picture. After I filled the form and provide the picture, I pressed a "save" button, which is basically sending all those information and pictures to firebase and then return to the main activity. Before the main activity appears, the app crashed and this error appears:
2022-08-16 20:49:53.847 21445-21445/com.example.gesit E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.gesit, PID: 21445
java.lang.NullPointerException: Attempt to invoke virtual method 'void com.google.android.material.button.MaterialButton.setEnabled(boolean)' on a null object reference
at com.example.gesit.TambahProduk.saveProductInformation$lambda-6(TambahProduk.kt:313)
at com.example.gesit.TambahProduk.$r8$lambda$WSqVgd-3d_M5F9vVqHMPnqwiv5o(Unknown Source:0)
at com.example.gesit.TambahProduk$$ExternalSyntheticLambda3.onComplete(Unknown Source:2)
at com.google.android.gms.tasks.zzi.run(com.google.android.gms:play-services-tasks##18.0.1:1)
at android.os.Handler.handleCallback(Handler.java:938)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loopOnce(Looper.java:226)
at android.os.Looper.loop(Looper.java:313)
at android.app.ActivityThread.main(ActivityThread.java:8751)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:571)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1135)
What caused this crash? Thanks.
Code for sending data and picture to firebase:
private fun saveProductInformation(downloadedUrl: String) {
auth = FirebaseAuth.getInstance()
val uid = auth.currentUser?.uid.toString()
databaseReference =
FirebaseDatabase.getInstance()
.getReference("User")
val productName = productName.text.toString()
val productInfo =
DataProduk(productName, uid)
if (uid != null) {
databaseReference.child(uid).setValue(productInformation)
.addOnCompleteListener {
saveButton.isEnabled = false
Toast.makeText(this#AddProduct,"Product added",Toast.LENGTH_SHORT).show()
hideProgressBar()
}
}
}

Showing dialog in MVVM Android throws exception only when certain variable changes in the ViewModel

I have a MainActivity using a DrawerLayout and tabs with 2 fragments.
My first fragment contains a list of elements in a RecyclerView, and I can click on each element to "select" it (which calls a SDK function to login to a hardware device). When selected, this triggers a change on the Fragment's ViewModel:
// Selected device changes when an item is clicked
private val _devices = MutableLiveData<List<DeviceListItemViewModel>>()
private val _selectedDevice = MutableLiveData<ConnectedDevice>()
val devices: LiveData<List<DeviceListItemViewModel>> by this::_devices
val selectedDevice: LiveData<ConnectedDevice> by this::_selectedDevice
Then I have a shared ViewModel between both fragments, which also has a currentDevice variable like this:
private val _currentDevice = MutableLiveData<ConnectedDevice>()
val currentDevice: LiveData<ConnectedDevice> by this::_currentDevice
So in the Fragment that contains the list, I have the following code to update the shared ViewModel variable:
private val mViewModel: DeviceManagementViewModel by viewModels()
private val mSharedViewModel: MainActivityViewModel by activityViewModels()
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
Log.d(classTag, "Fragment view created")
val binding = ActivityMainDevicesManagementFragmentBinding.bind(view)
binding.apply {
viewModel = mViewModel
lifecycleOwner = viewLifecycleOwner
}
// Observe fragment ViewModel
// If any device is clicked on the list, do the login on the shared ViewModel
mViewModel.selectedDevice.observe(this, {
mSharedViewModel.viewModelScope.launch {
if (it != null) {
mSharedViewModel.setCurrentDevice(videoDevice = it)
} else mSharedViewModel.unsetCurrentDevice()
}
})
}
The problem is that if the shared ViewModel's currentDevice variable is set, I get exceptions whenever I try to open a Dialog or start a new activity. If I modify the setCurrentDevice function in the shared ViewModel, then it works fine (or if I don't select any device).
The exceptions I see are this when starting a new Activity:
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.placeholder.easyview/com.example.myapp.activities.settings.SettingsActivity}: java.lang.IllegalArgumentException: display must not be null
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3430)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3594)
at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:85)
at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135)
at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2067)
at android.os.Handler.dispatchMessage(Handler.java:106)
at android.os.Looper.loop(Looper.java:223)
at android.app.ActivityThread.main(ActivityThread.java:7698)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:592)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:952)
Caused by: java.lang.IllegalArgumentException: display must not be null
at android.app.ContextImpl.createDisplayContext(ContextImpl.java:2386)
at android.content.ContextWrapper.createDisplayContext(ContextWrapper.java:977)
at com.android.internal.policy.DecorContext.<init>(DecorContext.java:50)
at com.android.internal.policy.PhoneWindow.generateDecor(PhoneWindow.java:2348)
at com.android.internal.policy.PhoneWindow.installDecor(PhoneWindow.java:2683)
at com.android.internal.policy.PhoneWindow.getDecorView(PhoneWindow.java:2116)
at androidx.appcompat.app.AppCompatActivity.initViewTreeOwners(AppCompatActivity.java:219)
at androidx.appcompat.app.AppCompatActivity.setContentView(AppCompatActivity.java:194)
at com.example.myapp.activities.settings.SettingsActivity.onCreate(SettingsActivity.kt:34)
at android.app.Activity.performCreate(Activity.java:8000)
at android.app.Activity.performCreate(Activity.java:7984)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1310)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3403)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3594) 
at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:85) 
at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135) 
at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95) 
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2067) 
at android.os.Handler.dispatchMessage(Handler.java:106) 
at android.os.Looper.loop(Looper.java:223) 
at android.app.ActivityThread.main(ActivityThread.java:7698) 
at java.lang.reflect.Method.invoke(Native Method) 
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:592) 
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:952) 
And this if I try to open a Dialog:
java.lang.ArrayIndexOutOfBoundsException: length=16; index=2448
at android.view.InsetsState.peekSource(InsetsState.java:374)
at android.view.InsetsSourceConsumer.updateSource(InsetsSourceConsumer.java:291)
at android.view.InsetsController.updateState(InsetsController.java:654)
at android.view.InsetsController.onStateChanged(InsetsController.java:621)
at android.view.ViewRootImpl.setView(ViewRootImpl.java:1058)
at android.view.WindowManagerGlobal.addView(WindowManagerGlobal.java:409)
at android.view.WindowManagerImpl.addView(WindowManagerImpl.java:110)
at android.app.Dialog.show(Dialog.java:340)
at android.app.AlertDialog$Builder.show(AlertDialog.java:1131)
at com.example.myapp.activities.main.fragments.DeviceManagementFragment.showAddDeviceMethodDialog(DeviceManagementFragment.kt:151)
at com.example.myapp.activities.main.fragments.DeviceManagementFragment.access$showAddDeviceMethodDialog(DeviceManagementFragment.kt:33)
at com.example.myapp.activities.main.fragments.DeviceManagementFragment$onViewCreated$$inlined$apply$lambda$1.onClick(DeviceManagementFragment.kt:52)
at android.view.View.performClick(View.java:7448)
at android.view.View.performClickInternal(View.java:7425)
at android.view.View.access$3600(View.java:810)
at android.view.View$PerformClick.run(View.java:28309)
at android.os.Handler.handleCallback(Handler.java:938)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:223)
at android.app.ActivityThread.main(ActivityThread.java:7698)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:592)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:952)
EDIT: Looks like the problem actually lies in the other fragment, where I have the following code (in onViewCreated method):
// If the shared view model device changes, this must change too
mSharedViewModel.currentDevice.observe(this, {
if (it != null) {
mViewModel.setCurrentDevice(it)
} else mViewModel.unsetCurrentDevice()
})
mViewModel.currentDevice.observe(this, {
if (it != null) {
mViewModel.fetchChannels()
}
})
If I comment out the second part (where the fetchChannels occurs), it works well. Even if I comment out the fetchChannels call only, it works.
This is the code of the fetchChannels function:
fun fetchChannels() = viewModelScope.launch {
Log.d(classTag, "Getting channels for device ${currentDevice.value}")
currentDevice.value?.let {
val fetchedChannels = deviceLibManager.getChannels(it.videoDevice)
_currentDevice.value?.channels?.clear()
_currentDevice.value?.channels?.addAll(fetchedChannels)
if (fetchedChannels.isNotEmpty()) {
_currentDevice.value?.currentChannel = fetchedChannels[0]
}
}
}
The following line is the one giving me trouble:
val fetchedChannels = deviceLibManager.getChannels(it.videoDevice)
That function is just this:
suspend fun getChannels(videoDevice: VideoDevice): List<VideoChannel> {
try {
Log.i(classTag, "Getting channels from device ${videoDevice}")
val channels = videoDevice.getChannelsAsync()
return channels
} catch (exception: Exception) {
when (exception) {
is UnknownVendorException -> {
Log.w(classTag, "Device ${videoDevice} cannot get channels because the vendor is unknown")
}
is NetworkException -> {
Log.w(classTag, "Device ${videoDevice} cannot get channels because it is unreachable")
}
else -> {
Log.w(classTag, "Device ${videoDevice} cannot get channels, reason: ${exception.message}")
}
}
return emptyList()
}
}
And the implementation in the SDK is this:
override suspend fun getChannelsAsync(): List<VideoChannel> = withContext(Dispatchers.IO) {
Log.i(classTag, "Trying to get channels for device: $logName")
val channels = ArrayList<VideoChannel>()
getZeroChannel()?.let {
channels.add(it)
}
channels.addAll(getAllChannels())
if (channels.isNotEmpty()) {
Log.i(classTag, "Successfully retrieved ${channels.size} channels for device: $logName")
return#withContext channels
} else {
Log.w(classTag, "Error retrieving channels for device $logName or no channels exist")
throw Exception()
}
}
The other functions just make a network call and retrieve some data, it should not be messing with the UI at all.
I am testing with a Xiaomi Mi A3 using Android 10.
Can someone help me? Thank you.

So I don't really know why but I found the answer.
In the SDK, the functions getZeroChannel and getAllChannels were not suspending functions, although they make a network call. So what I did is:
Move the withContext(Dispatchers.IO) part to those two functions (the ones who actually make the network call), and make them suspend functions.
Remove the withContext(Dispatchers.IO) part from getChannelsAsync function. Keep it as a suspend function though.
After these changes everything works as expected. I still don't know why, so if someone could shed some light, that would be very much appreciated.

Android Studio kotlin app "keep stopping" error

package com.example.absolutelydumb
import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import android.text.InputType
import android.widget.Button
import android.widget.EditText
import android.widget.TextView
import kotlinx.android.synthetic.main.activity_main.*
//sets var to some random number and asks for a guess, giving feedback on proximity to answer
class MainActivity : AppCompatActivity() {
private val startButton: Button = findViewById(R.id.startButton)
private val submitButton: Button = findViewById(R.id.submit)
private val instructionsText: TextView = findViewById(R.id.instructionView)
private val response: EditText = findViewById(R.id.answerInput)
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
val startText: String = getString(R.string.startText)
startButton.text = startText
//TODO("Add autofillHints")
startButton.setOnClickListener {
numberGuess()
}
//TODO("Set text back to start after guessing is done")
}
fun numberGuess() {
response.inputType = InputType.TYPE_CLASS_NUMBER
val clickText: String = getString(R.string.clickText)
startButton.text = clickText
//TODO("Add autofillHints")
instructionsText.text = getString(R.string.instructions)
val randomNumber: Int = rand(0,10)
submitButton.setOnClickListener {
val responseText = Integer.parseInt(answerInput.text.toString())
if(responseText == randomNumber) {
instructionsText.text = getString(R.string.correctGuess)
} else {
instructionsText.text = getString(R.string.badGuess)
}
}
}
fun rand(start: Int, end: Int): Int {
//require(start <= end) { "Illegal Argument" }
return (start..end).random()
}
}
Above is the code that I've been writing. This is my first project, so I don't know what went wrong. I fixed a variable type problem in the numberGuess function but when I finished fixing it the app wouldn't open and the virtual device stated a "app keeps stopping" error.
Here is the Run log that lists off errors. The build log didn't have any errors.
07/09 19:58:05: Launching 'app' on phone1.
Install successfully finished in 1 s 266 ms.
$ adb shell am start -n "com.example.absolutelydumb/com.example.absolutelydumb.MainActivity" -a android.intent.action.MAIN -c android.intent.category.LAUNCHER
Connected to process 5935 on device 'phone1 [emulator-5554]'.
Capturing and displaying logcat messages from application. This behavior can be disabled in the "Logcat output" section of the "Debugger" settings page.
D/AndroidRuntime: Shutting down VM
E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.absolutelydumb, PID: 5935
java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.absolutelydumb/com.example.absolutelydumb.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.pm.ApplicationInfo android.content.Context.getApplicationInfo()' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2843)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3048)
at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:78)
at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:108)
at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:68)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1808)
at android.os.Handler.dispatchMessage(Handler.java:106)
at android.os.Looper.loop(Looper.java:193)
at android.app.ActivityThread.main(ActivityThread.java:6669)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.pm.ApplicationInfo android.content.Context.getApplicationInfo()' on a null object reference
at android.content.ContextWrapper.getApplicationInfo(ContextWrapper.java:159)
at android.view.ContextThemeWrapper.getTheme(ContextThemeWrapper.java:157)
at android.content.Context.obtainStyledAttributes(Context.java:675)
at androidx.appcompat.app.AppCompatDelegateImpl.createSubDecor(AppCompatDelegateImpl.java:692)
at androidx.appcompat.app.AppCompatDelegateImpl.ensureSubDecor(AppCompatDelegateImpl.java:659)
at androidx.appcompat.app.AppCompatDelegateImpl.findViewById(AppCompatDelegateImpl.java:479)
at androidx.appcompat.app.AppCompatActivity.findViewById(AppCompatActivity.java:214)
at com.example.absolutelydumb.MainActivity.<init>(MainActivity.kt:13)
at java.lang.Class.newInstance(Native Method)
at android.app.AppComponentFactory.instantiateActivity(AppComponentFactory.java:69)
at androidx.core.app.CoreComponentFactory.instantiateActivity(CoreComponentFactory.java:45)
at android.app.Instrumentation.newActivity(Instrumentation.java:1215)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2831)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3048) 
at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:78) 
at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:108) 
at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:68) 
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1808) 
at android.os.Handler.dispatchMessage(Handler.java:106) 
at android.os.Looper.loop(Looper.java:193) 
at android.app.ActivityThread.main(ActivityThread.java:6669) 
at java.lang.reflect.Method.invoke(Native Method) 
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493) 
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858) 

You cannot call findViewById before onCreate() or setContentView() is called. Since you are using findViewById at the declaration site of your four properties, it is being called at the time your Activity class is being instantiated, which is before onCreate is called.
There are two ways to handle this.
Use lateinit var and set the properties right after your call to setContentView():
private lateinit var startButton: Button
//...
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
button = findViewById(R.id.startButton)
//...
Use by lazy so it is only called when the property is first accessed, which will be after setContentView() is called:
private val startButton: Button by lazy { findViewById(R.id.startButton) }
Or you can use view binding, which gets rid of most of this boilerplate and is less error-prone. By error-prone, I mean you can call findViewById and accidentally search for a view that isn't present in the current layout and it will crash at runtime. View binding makes this impossible.