App crashes on First Open only when AdMob is added but working fine on next open

Question

My App is working fine and then I tried to add AdMob dependencies. That's when things get complicated. On first install and then open App crashes. But on second and consecutive open the app is working fine, all ads are showing.

For me, this is a bad user experience because at first open they think it is not a good app. And maybe they will uninstall it immediately.

Maybe there's something I need to improve or add but I can't figure it out. I need help regarding polishing my code.

Android Manifest

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.gumangan.uecfispiritualhymns">

<uses-permission android:name="android.permission.INTERNET" />

<application
    android:allowBackup="true"
    android:icon="@mipmap/ic_launcher"
    android:label="@string/app_name"
    android:roundIcon="@mipmap/ic_launcher_round"
    android:supportsRtl="true"
    android:theme="@style/AppTheme">

    <!-- TODO: Change android:value when final building  -->
    <!--Sample AdMob App ID: ca-app-pub-3940256099942544~3347511713-->
    <meta-data
        android:name="com.google.android.gms.ads.APPLICATION_ID"
        android:value="ca-app-pub-3940256099942544~3347511713"/>

    <activity
        android:name="com.gumangan.uecfispiritualhymns.DictionaryActivity"
        android:label="@string/app_name"
        android:launchMode="singleTop"
        android:theme="@style/AppTheme.NoActionBar">
        <intent-filter>
            <action android:name="android.intent.action.MAIN" />

            <category android:name="android.intent.category.LAUNCHER" />

            <action android:name="android.intent.action.SEARCH" />
        </intent-filter>

        <meta-data
            android:name="android.app.searchable"
            android:resource="@xml/searchable" />
    </activity>
    <activity 
android:name="com.gumangan.uecfispiritualhymns.WordDetailActivity"

android:parentActivityName="com.gumangan.uecfispiritualhymns.DictionaryActivity">

android:value="com.gumangan.uecfispiritualhymns.DictionaryActivity"/>
    </activity>
</application>

Gradle Properties

// Top-level build file where you can add configuration options common to all sub-projects/modules.

buildscript {
ext.kotlin_version = '1.3.10'
repositories {
    google()
    jcenter()
}
dependencies {
    classpath 'com.android.tools.build:gradle:3.2.1'
    classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version"

    // NOTE: Do not place your application dependencies here; they belong
    // in the individual module build.gradle files
}
}

allprojects {
repositories {
    google()
    jcenter()
    maven {
        url "https://maven.google.com"
    }
}
}

task clean(type: Delete) {
delete rootProject.buildDir
}

Gradle Dependencies

apply plugin: 'com.android.application'

apply plugin: 'kotlin-android'

apply plugin: 'kotlin-android-extensions'

android {
compileSdkVersion 27
defaultConfig {
    applicationId "com.gumangan.uecfispiritualhymns"
    minSdkVersion 16
    targetSdkVersion 27
    versionCode 1
    versionName "1.0"
    testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
}
buildTypes {
    release {
        minifyEnabled false
        proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
    }
}
}

dependencies {
implementation fileTree(dir: 'libs', include: ['*.jar'])
implementation "org.jetbrains.kotlin:kotlin-stdlib-jdk7:$kotlin_version"
implementation 'com.android.support:appcompat-v7:27.1.1'
implementation 'com.android.support:support-v4:27.1.1'
implementation 'com.android.support.constraint:constraint-layout:1.1.3'
implementation 'com.android.support:design:27.1.1'
implementation 'com.android.support:cardview-v7:27.1.1'
implementation 'com.android.support:customtabs:27.1.1'

implementation 'com.google.android.gms:play-services-ads:17.1.2'

testImplementation 'junit:junit:4.12'
androidTestImplementation 'com.android.support.test:runner:1.0.2'
androidTestImplementation 'com.android.support.test.espresso:espresso-core:3.0.2'
}

DatabaseHelper

package com.gumangan.uecfispiritualhymns

import android.content.Context
import android.database.Cursor
import android.database.sqlite.SQLiteDatabase
import android.database.sqlite.SQLiteOpenHelper
import android.preference.PreferenceManager

import java.io.FileOutputStream
import java.io.IOException
import java.io.InputStream
import java.io.OutputStream

class DatabaseHelper(private var mContext: Context) : SQLiteOpenHelper(mContext, DATABASE_NAME, null, DATABASE_VERSION) {
companion object {
    private val DATABASE_NAME = "simple_dict.db"
    private val DATABASE_VERSION = 1
    val DB_CREATED = "DB_CREATED"
}

private var mCreateDb = false
private var mUpgradeDb = false

private fun copyDatabaseFromAssets(db: SQLiteDatabase?) {
    var inputStream: InputStream? = null
    var outputStream: OutputStream? = null

    try {
        inputStream = mContext.assets.open(DATABASE_NAME)
        outputStream = FileOutputStream(db?.path)

        val buffer = ByteArray(1024)
        var length: Int = inputStream!!.read(buffer)
        while (length > 0) {
            outputStream.write(buffer, 0, length)
            length = inputStream.read(buffer)
        }
        outputStream.flush()

        val  copiedDb = mContext.openOrCreateDatabase(DATABASE_NAME, 0, null)

        val isDbCreated = copiedDb != null

        copiedDb.execSQL("PRAGMA user_version = $DATABASE_VERSION")
        copiedDb.close()

        // DB_CREATED
        val sharedPref = PreferenceManager.getDefaultSharedPreferences(mContext)
        val sharePrefEditor = sharedPref.edit()
        sharePrefEditor.putBoolean(DB_CREATED, isDbCreated)
        sharePrefEditor.apply()
    } catch (e: IOException) {
        e.printStackTrace()
        throw Error("copyDatabaseFromAssets: Error copying database.")
    } finally {
        try {
            outputStream?.close()
            inputStream?.close()
        }catch (e: IOException) {
            e.printStackTrace()
            throw Error("copyDatabaseFromAssets: Error closing stream.")
        }
    }

}

override fun onCreate(db: SQLiteDatabase?) {
    mCreateDb = true
}

override fun onUpgrade(db: SQLiteDatabase?, oldVersion: Int, newVersion: Int) {
    if(newVersion > oldVersion) {
        mUpgradeDb = true
    }
}

override fun onOpen(db: SQLiteDatabase?) {
    if(mCreateDb) {
        mCreateDb = false
        copyDatabaseFromAssets(db)
    }

    if(mUpgradeDb) {
        mUpgradeDb = false
        copyDatabaseFromAssets(db)
    }
}

fun getWords(wordPrefix: String = ""): Cursor {
    return if(wordPrefix.isBlank()) {
        readableDatabase.query(DictionaryEntryContract.TABLE_NAME, null,
                null, null, null, null,
                "${DictionaryEntryContract.COLUMN_ID} ASC")
    } else {
        readableDatabase.query(DictionaryEntryContract.TABLE_NAME, null,
                "${DictionaryEntryContract.COLUMN_WORD} LIKE ?", arrayOf("$wordPrefix%"),
                null, null, "${DictionaryEntryContract.COLUMN_ID} ASC")
    }
}

fun getWord(id: String): Cursor {
    return readableDatabase.query(DictionaryEntryContract.TABLE_NAME, null,
            "${DictionaryEntryContract.COLUMN_ID}= ?", arrayOf(id),
            null, null, null)
}
}

SearchListAdapter

package com.gumangan.uecfispiritualhymns

import android.content.Context
import android.database.Cursor
import android.graphics.Color
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import android.widget.CursorAdapter
import android.widget.TextView

class SearchListAdapter(context: Context, cursor: Cursor) : CursorAdapter(context, cursor, 0) {
private class ViewHolder {
    var txtWord: TextView? = null
    var txtType: TextView? = null
    var txtMeaning: TextView? = null

    var wordColumnIndex: Int = 0
    var typeColumnIndex: Int = 0
    var meaningColumnIndex: Int = 0
}

override fun newView(context: Context?, cursor: Cursor?, parent: ViewGroup?): View {
    val layoutInflater = LayoutInflater.from(context)
    val newView = layoutInflater.inflate(R.layout.search_list_item, parent, false)

    val viewHolder = ViewHolder()
    viewHolder.txtWord = newView.findViewById<TextView>(R.id.txtWord)
    viewHolder.txtType = newView.findViewById<TextView>(R.id.txtType)
    viewHolder.txtMeaning = newView.findViewById<TextView>(R.id.txtMeaning)

    viewHolder.wordColumnIndex = cursor!!.getColumnIndexOrThrow(DictionaryEntryContract.COLUMN_WORD)
    viewHolder.typeColumnIndex = cursor!!.getColumnIndexOrThrow(DictionaryEntryContract.COLUMN_TYPE)
    viewHolder.meaningColumnIndex = cursor!!.getColumnIndexOrThrow(DictionaryEntryContract.COLUMN_MEANING)

    newView.tag = viewHolder

    return newView
}

override fun bindView(view: View?, context: Context?, cursor: Cursor?) {
    val viewHolder = view!!.tag as ViewHolder

    viewHolder.txtWord?.text = cursor?.getString(viewHolder.wordColumnIndex)
    viewHolder.txtType?.text = cursor?.getString(viewHolder.typeColumnIndex)
    viewHolder.txtMeaning?.text = cursor?.getString(viewHolder.meaningColumnIndex)
}

override fun getView(position: Int, convertView: View?, parent: ViewGroup?): View {
    val view = super.getView(position, convertView, parent)

    if(position % 2 == 0) {
        view.setBackgroundColor(Color.LTGRAY)
    } else {
        view.setBackgroundColor(Color.WHITE)
    }

    return view;
}
}

DictionaryEntryContract

package com.gumangan.uecfispiritualhymns

import android.provider.BaseColumns

class DictionaryEntryContract : BaseColumns {
private constructor()

companion object {
    val TABLE_NAME = "english_words"

    val COLUMN_ID = BaseColumns._ID
    val COLUMN_WORD = "word"
    val COLUMN_TYPE = "type"
    val COLUMN_MEANING = "meaning"
}
}

DictionaryActivity

package com.gumangan.uecfispiritualhymns

import android.app.SearchManager
import android.content.Context
import android.content.Intent
import android.os.AsyncTask
import android.os.Bundle
import android.preference.PreferenceManager
import android.support.v7.app.AppCompatActivity
import android.support.v7.widget.Toolbar
import android.support.v7.widget.SearchView
import android.util.Log
import android.view.Menu
import android.view.MenuItem
import android.widget.AdapterView
import android.widget.ListView
import com.google.android.gms.ads.AdRequest
import com.google.android.gms.ads.AdView
import com.google.android.gms.ads.MobileAds
import java.lang.ref.WeakReference

class DictionaryActivity : AppCompatActivity() {

companion object {
    val TAG = "DictionaryActivity"
    val LAST_SEARCH_WORD: String = "LAST_SEARCH_WORD"
}

var mDbHelper: DatabaseHelper? = null
private var mSearchListAdapter: SearchListAdapter? = null
private var mSearchQuery: String = ""

//Google Ads Banner Variable
lateinit var mAdView : AdView

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

    mSearchQuery = savedInstanceState?.getString(LAST_SEARCH_WORD) ?: ""
    mDbHelper = DatabaseHelper(applicationContext)

    if(!isDbLoaded()) {
        showLoadingUI()
        LoadViewTask(this).execute()
    } else {
        showDictUI()
    }

    /* TODO: Change ADMOB ID's when final building  */
    //Google Ads
    //MobileAds.initialize(this, "ca-app-pub-3940256099942544~3347511713")
    //Google Test Ads
    MobileAds.initialize(this, "ca-app-pub-3940256099942544~3347511713")

    //Google Ads Banner
    mAdView = findViewById(R.id.adView)
    val adRequest = AdRequest.Builder().build()
    mAdView.loadAd(adRequest)

}

private fun isDbLoaded(): Boolean {
    val sharedPref = PreferenceManager.getDefaultSharedPreferences(this)
    return sharedPref.getBoolean(DatabaseHelper.DB_CREATED, false)
}

private fun showLoadingUI() {
    setContentView(R.layout.activity_dictionary_loading)
}

private fun showDictUI() {
    setContentView(R.layout.activity_dictionary)

    val toolbar = findViewById<Toolbar>(R.id.toolbar)
    setSupportActionBar(toolbar)

    supportActionBar?.setIcon(R.mipmap.ic_launcher)

    mSearchListAdapter = SearchListAdapter(applicationContext, mDbHelper!!.getWords(mSearchQuery))
    val lstWords = (findViewById<ListView>(R.id.lstWords))
    lstWords.adapter = mSearchListAdapter
    lstWords.onItemClickListener = AdapterView.OnItemClickListener { _, _, _, id ->
        val wordDetailIntent = Intent(applicationContext, WordDetailActivity::class.java)
        wordDetailIntent.putExtra(WordDetailActivity.WORD_ID, "$id")
        startActivity(wordDetailIntent)
    }
}

override fun onSaveInstanceState(outState: Bundle?) {
    super.onSaveInstanceState(outState)
    outState?.putString(LAST_SEARCH_WORD, mSearchQuery)
}

override fun onRestoreInstanceState(savedInstanceState: Bundle?) {
    mSearchQuery = savedInstanceState?.getString(LAST_SEARCH_WORD) ?: ""
    super.onRestoreInstanceState(savedInstanceState)
}

override fun onNewIntent(intent: Intent?) {
    super.onNewIntent(intent)

    if(intent?.action.equals(Intent.ACTION_SEARCH)) {
        val searchQuery = intent?.getStringExtra(SearchManager.QUERY) ?: ""
        updateListByQuery(searchQuery)
    }
}

override fun onCreateOptionsMenu(menu: Menu): Boolean {
    menuInflater.inflate(R.menu.menu_dictionary, menu)

    val searchView: SearchView? = menu.findItem(R.id.action_search).actionView as? SearchView
    val searchManager: SearchManager = getSystemService(Context.SEARCH_SERVICE) as SearchManager
    searchView?.setSearchableInfo(searchManager.getSearchableInfo(componentName))

    searchView?.setOnQueryTextListener(object : SearchView.OnQueryTextListener{
        override fun onQueryTextSubmit(query: String?): Boolean {
            return false
        }

        override fun onQueryTextChange(newText: String?): Boolean {
            updateListByQuery(newText ?: "")
            return true
        }
    })

    return true
}

private fun updateListByQuery(searchQuery: String) {
    mSearchQuery = searchQuery
    mSearchListAdapter?.changeCursor(mDbHelper!!.getWords(searchQuery))
}

override fun onOptionsItemSelected(item: MenuItem): Boolean {
    return when (item.itemId) {
        R.id.action_search -> {
            onSearchRequested()
            true
        }
        else -> super.onOptionsItemSelected(item)
    }
}

private class LoadViewTask(activity: DictionaryActivity) : AsyncTask<Void, Void, Void>() {
    private var mActivity = WeakReference<DictionaryActivity>(activity)

    override fun doInBackground(vararg params: Void): Void? {
        if(getActivityInstance()?.mDbHelper?.readableDatabase?.isOpen == true) {
            Log.d(TAG, "Db is OK.")
        }
        return null
    }

    override fun onPostExecute(result: Void?) {
        if(getActivityInstance()?.isDbLoaded() == true) {
            getActivityInstance()?.showDictUI()
        }
    }

    private fun getActivityInstance() = mActivity.get()
}
}

WordDetailActivity

package com.gumangan.uecfispiritualhymns

import android.support.v7.app.AppCompatActivity
import android.os.Bundle
import android.widget.TextView

class WordDetailActivity : AppCompatActivity() {

companion object {
    const val WORD_ID = "WORD_ID"
}

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

    val wordId = intent.getStringExtra(WORD_ID) ?: ""
    if(wordId.isBlank()) {
        finish()
    }

    val dbHelper = DatabaseHelper(applicationContext)
    val cursor = dbHelper.getWord(wordId)
    if(cursor.moveToFirst()) {
        val txtWord = findViewById<TextView>(R.id.txtWord)
        val txtType = findViewById<TextView>(R.id.txtType)
        val txtMeaning = findViewById<TextView>(R.id.txtMeaning)

        txtWord?.text = cursor.getString(cursor.getColumnIndexOrThrow(DictionaryEntryContract.COLUMN_WORD))
        txtType?.text = cursor.getString(cursor.getColumnIndexOrThrow(DictionaryEntryContract.COLUMN_TYPE))
        txtMeaning?.text = cursor.getString(cursor.getColumnIndexOrThrow(DictionaryEntryContract.COLUMN_MEANING))
    }
}
}

activity_dictionary.xml

<?xml version="1.0" encoding="utf-8"?>
<android.support.design.widget.CoordinatorLayout 
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context="com.gumangan.uecfispiritualhymns.DictionaryActivity">

<android.support.design.widget.AppBarLayout
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:theme="@style/AppTheme.AppBarOverlay">

    <android.support.v7.widget.Toolbar
        android:id="@+id/toolbar"
        android:layout_width="match_parent"
        android:layout_height="?attr/actionBarSize"
        android:background="?attr/colorPrimary"
        app:popupTheme="@style/AppTheme.PopupOverlay" />

</android.support.design.widget.AppBarLayout>

<include layout="@layout/content_dictionary" />

</android.support.design.widget.CoordinatorLayout>

content_dictionary.xml

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout 
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
app:layout_behavior="@string/appbar_scrolling_view_behavior"
tools:context="com.gumangan.uecfispiritualhymns.DictionaryActivity"
tools:showIn="@layout/activity_dictionary">

<ListView
    android:id="@+id/lstWords"
    android:layout_width="0dp"
    android:layout_height="0dp"
    android:layout_marginBottom="0dp"
    android:layout_marginEnd="0dp"
    android:layout_marginStart="0dp"
    android:layout_marginTop="0dp"
    app:layout_constraintBottom_toBottomOf="parent"
    app:layout_constraintEnd_toEndOf="parent"
    app:layout_constraintStart_toStartOf="parent"
    app:layout_constraintTop_toTopOf="parent" />


    <!--Google Ads Banner Display-->
    <com.google.android.gms.ads.AdView
        xmlns:ads="http://schemas.android.com/apk/res-auto"
        android:id="@+id/adView"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentBottom="true"
        android:layout_centerHorizontal="true"
        android:layout_marginBottom="5dp"
        android:visibility="visible"
        ads:adSize="LARGE_BANNER"
        ads:adUnitId="ca-app-pub-3940256099942544/6300978111"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent">

    </com.google.android.gms.ads.AdView>

</android.support.constraint.ConstraintLayout>

activity_dictionary_loading.xml

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout 
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context="com.gumangan.uecfispiritualhymns.DictionaryActivity">

<TextView
    android:id="@+id/textView"
    android:layout_width="0dp"
    android:layout_height="wrap_content"
    android:layout_marginBottom="8dp"
    android:layout_marginEnd="8dp"
    android:layout_marginStart="8dp"
    android:layout_marginTop="8dp"
    android:text="@string/dictionary_db_preparing"
    android:textAlignment="center"
    android:textSize="18sp"
    app:layout_constraintBottom_toBottomOf="parent"
    app:layout_constraintEnd_toEndOf="parent"
    app:layout_constraintStart_toStartOf="parent"
    app:layout_constraintTop_toTopOf="parent"
    tools:text="@string/dictionary_db_preparing" />
</android.support.constraint.ConstraintLayout>

search_list_item.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
android:padding="16dp">

<TextView
    android:id="@+id/txtWord"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:textSize="18sp"
    android:textStyle="bold"
    tools:text="Word" />

<TextView
    android:id="@+id/txtType"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:textSize="14sp"
    android:textStyle="italic"
    tools:text="Type" />

<TextView
    android:id="@+id/txtMeaning"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:textSize="18sp"
    tools:text="Meaning" />
</LinearLayout>

activity_word_detail.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
android:padding="16dp"
tools:context="com.gumangan.uecfispiritualhymns.WordDetailActivity">

<TextView
    android:id="@+id/txtWord"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:textSize="20sp"
    android:textStyle="bold"
    tools:text="Word" />

<TextView
    android:id="@+id/txtType"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:textSize="18sp"
    android:textStyle="italic"
    tools:text="Type" />

<TextView
    android:id="@+id/txtMeaning"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:textSize="20sp"
    tools:text="Meaning" />

</LinearLayout>

This is the LogCat error

12-09 07:52:40.554 14146-14146/com.gumangan.uecfispiritualhymns E/AndroidRuntime: FATAL EXCEPTION: main
    java.lang.RuntimeException: Unable to start activity
ComponentInfo{com.gumangan.uecfispiritualhymns/com.gumangan.uecfispiritualhymns.DictionaryActivity}: java.lang.IllegalStateException: findViewById(R.id.adView) must not be null
        at 
    android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2059)
        at 
    android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2084)
        at android.app.ActivityThread.access$600(ActivityThread.java:130)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1195)
        at android.os.Handler.dispatchMessage(Handler.java:99)
        at android.os.Looper.loop(Looper.java:137)
        at android.app.ActivityThread.main(ActivityThread.java:4745)
        at java.lang.reflect.Method.invokeNative(Native Method)
        at java.lang.reflect.Method.invoke(Method.java:511)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
        at dalvik.system.NativeStart.main(Native Method)
     Caused by: java.lang.IllegalStateException: findViewById(R.id.adView) must not be null
        at com.gumangan.uecfispiritualhymns.DictionaryActivity.onCreate(DictionaryActivity.kt:57)
        at android.app.Activity.performCreate(Activity.java:5008)
        at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1079)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2023)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2084) 
        at android.app.ActivityThread.access$600(ActivityThread.java:130) 
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1195) 
        at android.os.Handler.dispatchMessage(Handler.java:99) 
        at android.os.Looper.loop(Looper.java:137) 
        at android.app.ActivityThread.main(ActivityThread.java:4745) 
        at java.lang.reflect.Method.invokeNative(Native Method) 
        at java.lang.reflect.Method.invoke(Method.java:511) 
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786) 
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553) 
        at dalvik.system.NativeStart.main(Native Method) 

The app is about dictionary

Answer 1

In your MainActivity.kt . Try replace this:

lateinit var mAdView: AdView

MobileAds.initialize(this, "ca-app-pub-3940256099942544~3347511713")

//Google Ads Banner
mAdView = findViewById(R.id.adView)
val adRequest = AdRequest.Builder().build()
mAdView.loadAd(adRequest)
mAdView.adListener = object: AdListener() {
    override fun onAdLoaded() {
        //adView.visibility = View.VISIBLE
        //divider.visibility = View.VISIBLE
        Toast.makeText(applicationContext,"Banner Ad Loaded", Toast.LENGTH_LONG).show()
    }
    override fun onAdFailedToLoad(errorCode : Int) {
        //adView.visibility = View.GONE
        //divider.visibility = View.GONE

        //Timer for Loading Ads
        Handler().postDelayed({

            mAdView.loadAd(adRequest)

        }, 300000)

        //mAdView.loadAd(adRequest)
        Toast.makeText(applicationContext,"Banner Ad Failed to Load", Toast.LENGTH_LONG).show()
    }
    override fun onAdOpened() {
        // Code to be executed when the ad is displayed.
    }
    override fun onAdLeftApplication() {
        // Code to be executed when the user has left the app.
    }
    override fun onAdClosed() {
        //mAdView.loadAd(adRequest)
        //Toast.makeText(applicationContext,"Banner Ad Loaded Again", Toast.LENGTH_LONG).show()
    }
}

with this:

import kotlinx.android.synthetic.main.content_main.*

MobileAds.initialize(this,"ca-app-pub-3940256099942544~3347511713")

adView.loadAd(AdRequest.Builder().build())

and make you sure that adView is visible.