Java 没有'；我找不到课堂咨询

我想在我的应用程序中添加AdMob，但在我的应用程序中找不到AdView类

build.gradle

...
dependencies {
   api ('com.google.android.gms:play-services-ads:16.0.0'){force = true}
   api fileTree(dir: 'libs', include: ['*.jar'])
}

layout.xml

...

    <com.google.android.gms.ads.AdView
        android:id="@+id/banner_ad"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_centerHorizontal="true"
        android:layout_alignParentBottom="true"
        app:adSize="FULL_BANNER"
        app:adUnitId="ca-app-pub-xxx/xxx"/>

...

---

另请参见此处：

在应用程序Gradle中添加以下内容

implementation 'com.google.firebase:firebase-ads:18.3.0'

那么

dependencies {
    compile 'com.google.android.gms:play-services-ads:8.4.0'
}

implementation 'com.google.firebase:firebase-ads:18.3.0'

            <com.google.android.gms.ads.AdView
                android:id="@+id/adView"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                ads:adSize="BANNER"
                ads:adUnitId="@string/ad_unit_id">
            </com.google.android.gms.ads.AdView>