GoogleMapが描写されない

前提・実現したいこと

GoogleMapAPIを利用したアプリを作っています。
そこで、GoogleMapをFragmentで表示したいのですが、見た感じAPIは読み込まれているはずなのにマップが表示されません。

発生している問題

AndroidStudioで新規プロジェクトを作るときに標準で用意されている「Googleマップ・アクティビティー」からソースコードはほぼ改変なしでコピペしましたが、左下にGoogleのロゴは出るものの、マップが出ません。(画像添付)

該当のソースコード

MainActivity.kt

kotlin
1package com.example.hogehoge
2
3import android.content.Intent
4import android.os.Bundle
5import android.widget.TextView
6import androidx.appcompat.app.AppCompatActivity
7import com.example.otukai_watch.ToDoList.ItemActivity
8import com.example.otukai_watch.VoiceChat.VoiceActivity
9import com.google.android.material.bottomnavigation.BottomNavigationView
10
11import kotlinx.android.synthetic.main.activity_main.*
12
13
14class MainActivity : AppCompatActivity() {
15
16    private lateinit var textMessage: TextView
17    private val onNavigationItemSelectedListener = BottomNavigationView.OnNavigationItemSelectedListener { item ->
18        when (item.itemId) {
19            R.id.navigation_home -> {
20                viewflipper.displayedChild=0
21                return@OnNavigationItemSelectedListener true
22            }
23            R.id.navigation_dashboard -> {
24                val intent = Intent(this, VoiceActivity::class.java)
25                startActivity(intent)
26            }
27            R.id.navigation_notifications -> {
28                val intent = Intent(this, ItemActivity::class.java)
29                startActivity(intent)
30            }
31        }
32        false
33    }
34
35    override fun onCreate(savedInstanceState: Bundle?) {
36        super.onCreate(savedInstanceState)
37        setContentView(R.layout.activity_main)
38        val navView: BottomNavigationView = findViewById(R.id.nav_view)
39
40        navView.setOnNavigationItemSelectedListener(onNavigationItemSelectedListener)
41    }
42
43}

MapFragment.kt

kotlin
1package com.example.hogehoge
2
3import android.os.Bundle
4import android.view.LayoutInflater
5import android.view.View
6import android.view.ViewGroup
7import androidx.appcompat.app.AppCompatActivity
8import androidx.fragment.app.Fragment
9import com.google.android.gms.maps.CameraUpdateFactory
10import com.google.android.gms.maps.GoogleMap
11import com.google.android.gms.maps.OnMapReadyCallback
12import com.google.android.gms.maps.SupportMapFragment
13import com.google.android.gms.maps.model.LatLng
14import com.google.android.gms.maps.model.MarkerOptions
15
16class mapFragment : AppCompatActivity(), OnMapReadyCallback {
17
18    private lateinit var mMap: GoogleMap
19
20    override fun onCreate(savedInstanceState: Bundle?) {
21        super.onCreate(savedInstanceState)
22        setContentView(R.layout.fragment_map)
23        // Obtain the SupportMapFragment and get notified when the map is ready to be used.
24        val mapFragment = supportFragmentManager
25            .findFragmentById(R.id.map) as SupportMapFragment
26        mapFragment.getMapAsync(this)
27    }
28
29 
30    override fun onMapReady(googleMap: GoogleMap) {
31        mMap = googleMap
32
33        // Add a marker in Sydney and move the camera
34        val sydney = LatLng(-34.0, 151.0)
35        mMap.addMarker(MarkerOptions().position(sydney).title("Marker in Sydney"))
36        mMap.moveCamera(CameraUpdateFactory.newLatLng(sydney))
37    }
38}

activity_main.xml

xml
1<?xml version="1.0" encoding="utf-8"?>
2<androidx.constraintlayout.widget.ConstraintLayout
3  xmlns:android="http://schemas.android.com/apk/res/android"
4  xmlns:app="http://schemas.android.com/apk/res-auto"
5  xmlns:tools="http://schemas.android.com/tools"
6  android:id="@+id/container"
7  android:layout_width="match_parent"
8  android:layout_height="match_parent"
9  tools:context=".MainActivity">
10
11  <com.google.android.material.bottomnavigation.BottomNavigationView
12    android:id="@+id/nav_view"
13    android:layout_width="0dp"
14    android:layout_height="wrap_content"
15    android:layout_marginEnd="0dp"
16    android:layout_marginStart="0dp"
17    android:background="?android:attr/windowBackground"
18    app:layout_constraintBottom_toBottomOf="parent"
19    app:layout_constraintLeft_toLeftOf="parent"
20    app:layout_constraintRight_toRightOf="parent"
21    app:menu="@menu/bottom_nav_menu"/>
22  <ViewFlipper
23    android:id="@+id/viewflipper"
24
25    android:layout_width="match_parent"
26    android:layout_height="0dp"
27    app:layout_constraintBottom_toTopOf="@+id/nav_view"
28    app:layout_constraintTop_toTopOf="parent"
29    app:layout_constraintEnd_toEndOf="parent"
30    app:layout_constraintStart_toStartOf="parent"
31
32  >
33    <include layout="@layout/activity_maps1"/>
34  </ViewFlipper>
35
36
37</androidx.constraintlayout.widget.ConstraintLayout>
38
39

fragment_map.xml

xml
1<?xml version="1.0" encoding="utf-8"?>
2<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
3             xmlns:tools="http://schemas.android.com/tools"
4             android:layout_width="match_parent"
5             android:layout_height="match_parent"
6             tools:context=".MainActivity">
7
8    <fragment
9            android:name="com.google.android.gms.maps.SupportMapFragment"
10            android:id="@+id/frg"
11            android:layout_width="match_parent"
12            android:layout_height="match_parent"/>
13
14</FrameLayout>

AndroidManifest.xml

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

    <!--
         The ACCESS_COARSE/FINE_LOCATION permissions are not required to use
         Google Maps Android API v2, but you must specify either coarse or fine
         location permissions for the 'MyLocation' functionality.
    -->
    <uses-permission android:name="android.permission.ACCESS_FINE_LOCATION"/>
    <uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE"/>
    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>
    <uses-permission android:name="android.permission.RECORD_AUDIO"/>

    <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">

        <meta-data
                android:name="com.google.android.geo.API_KEY"
                android:value="@string/google_maps_key"/> 

        <activity
                android:name=".MainActivity"
                android:label="@string/title_activity_maps">
            <intent-filter>
                <action android:name="android.intent.action.MAIN"/>

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


        <activity
                android:name=".ToDoList.ItemActivity"
                android:label="@string/title_activity_main2"
                android:theme="@style/AppTheme.NoActionBar">
        </activity>

        <activity
                android:name=".VoiceChat.VoiceActivity"
                android:label="@string/title_activity_main2"
                android:theme="@style/AppTheme.NoActionBar">
        </activity>

        <activity
                android:name=".VoiceChat.RecordListActivity"
                android:screenOrientation="portrait" />
    </application>

</manifest>

補足情報

Gradle プラグインバージョン: 3.4.2
Gradleバージョン: 5.1.1
kotlinバージョン: 1.3.41
minSdkVersion 21
targetSdkVersion 28
Android Studio 3.4.2
Build #AI-183.6156.11.34.5692245, built on June 27, 2019
JRE: 1.8.0_152-release-1343-b01 amd64
JVM: OpenJDK 64-Bit Server VM by JetBrains s.r.o
Windows 10 10.0