在我重新打开应用之前，AdMob 广告不会展示

Question

我正在尝试将 AdMob 横幅添加到我的应用中，但有一半时间它没有显示任何内容。 AdListener 甚至接到了对 onAdLoaded 的电话，我从来没有收到任何错误。
我注意到，如果广告没有显示，并且我将应用程序置于后台，广告就会开始显示。例如，如果我：

1. 关闭并重新打开应用程序
2. 开始全屏插页式广告
3. 启动应用内购买覆盖

所有这些操作都会触发以某种方式重绘/重新测量视图的更新。
我在onAdLoaded 中尝试了许多不同的方法来模拟这一点。

即使我没有收到任何错误，AdMob 是否也可能找不到匹配的广告？根据网站，匹配率为 98%。展示次数约为请求的三分之一。

我发现了更多具有类似问题的帖子（全部来自大约 7 年前），但他们的答案都不适用于我的情况：
Admob not showing up until phone is locked
AdMob won't show the banner until refresh or sign in to google plus
Android AdMob: addView doesn't show ad until return to activity
@ 987654324@

我试图让它工作超过两天。请看一下我的代码，我用解释对其进行了注释：

主活动：

private AdView adView;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    binding = ActivityMainBinding.inflate(getLayoutInflater());
    setContentView(binding.getRoot());
    if(privacyPolicyAcceptedAndHasNoPremium()){ //at first i check the shared preferences
        binding.adPlaceholder.setVisibility(View.VISIBLE); //the adPlaceholder starts as GONE when i set it to VISIBLE the rest of the content slides up
        List<String> testDevices = Arrays.asList(AdRequest.DEVICE_ID_EMULATOR, "...");
        RequestConfiguration requestConfiguration = new RequestConfiguration.Builder().setTestDeviceIds(testDevices).build();
        MobileAds.setRequestConfiguration(requestConfiguration);

        MobileAds.initialize(MainActivity.this, initializationStatus -> {});

        adView = new AdView(this); //i create the adView programmatically but using the xml view element causes the same problem
        adView.setAdSize(AdSize.LARGE_BANNER);
        adView.setAdUnitId("...");
        adView.setAdListener(new AdListener() {
            @Override
            public void onAdLoaded() { // this gets called so i think the ad is successfully downloaded from the google server. i put all kinds of code in here to force the adView to show
                //setContentView(binding.getRoot());
                //binding.adPlaceholder.addView(new View(MainActivity.this));
                //binding.adPlaceholder.forceLayout();
                //binding.constraintLayout.requestLayout();
                //adView.invalidate();
                //adView.bringToFront();
                //adView.setVisibility(AdView.GONE);
                //adView.setVisibility(AdView.VISIBLE);
                //adView.setBackgroundColor(Color.TRANSPARENT);
            }
        }
        AdRequest.Builder adRequestBuilder = new AdRequest.Builder();
        binding.adPlaceholder.addView(adView); //i add the adView into the empty LinearLayout. i tried to add it directly to binding.constraintLayout too.
        adView.loadAd(adRequestBuilder.build());
}

activity_main.xml：

<androidx.constraintlayout.widget.ConstraintLayout
    android:id="@+id/constraintLayout"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    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">

    <!-- this is the empty container into which i load the ads. it sits at the bottom of the screen and is not visible before an ad is showing -->
    <LinearLayout
        android:id="@+id/adPlaceholder"
        android:layout_width="match_parent"
        android:layout_height="100dp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        android:orientation="vertical"
        android:visibility="gone" />

    <!-- this MotionLayout contains the rest of the app (except the toolbar). it slides up when an ad is showing -->
    <androidx.constraintlayout.motion.widget.MotionLayout
        android:id="@+id/motionLayout"
        android:layout_width="match_parent"
        android:layout_height="0dp"
        app:layoutDescription="@xml/activity_main_scene"
        app:layout_constraintBottom_toTopOf="@+id/adPlaceholder"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        tools:context=".MainActivity">
    ...
    </androidx.constraintlayout.motion.widget.MotionLayout>

</androidx.constraintlayout.widget.ConstraintLayout>

清单：

<uses-permission android:name="android.permission.INTERNET" />
<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
<application ...>
    <meta-data
        android:name="com.google.android.gms.ads.APPLICATION_ID"
        android:value="..." />
    ...
</application>

编辑：

Answer 1

我终于找到了适合我的方法。

我只是将窗口背景颜色设置为它已有的颜色。这真的很快，不会重新创建活动。

但是我不知道为什么这有效，为什么只有这对我有效。我猜它以与其他问题的许多其他解决方案类似的方式更新视图。

adView.setAdListener(new AdListener() {
    @Override
    public void onAdLoaded() {
        super.onAdLoaded();
        getWindow().setBackgroundDrawableResource(R.color.background);
    }
}