Why onAdDismissedFullScreenContent is being called lately?

I have created a function to show interstitial ad before showing another activity. It's working but onAdDismissedFullScreenContent is being called 2-3 sec lately after closing the ad. It causes previous screen to stand-by. There's a chance to re-click the button to show the wanted Activity.

I really don't understand how to resolve this issue.

Here is my code:

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Button button = findViewById(R.id.button);
        button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                AdManager.showInterstitial(MainActivity.this, () -> {
                    Intent i = new Intent(MainActivity.this, MainActivity2.class);
                    startActivity(i);
                });
            }
        });
        AdManager.loadInterstitial(this);
    }
}

And this is Application Class:

public class App  extends Application {
    private static Context mContext;


    @Override
    public void onCreate() {
        super.onCreate();
        mContext = getApplicationContext();
        AdManager.Init(this);
    }

    public static Context getContext() {
        return mContext;
    }
}

AdManager Class:

public class AdManager {

    private static InterstitialAd mInterstitialAd;
    private static boolean loading, showing;


    public static void Init(Context context) {

        MobileAds.initialize(context, initializationStatus -> {
            loadInterstitial(context);
        });
    }


    public static void loadInterstitial(Context context) {

        if (context == null)
            context = App.getContext();

        Context finalContext = context;
        
        if (mInterstitialAd != null) {
            Toast.makeText(context,"already loaded",Toast.LENGTH_LONG).show();
            return;
        }
        if (loading) {
            Toast.makeText(context,"already another request is processing",Toast.LENGTH_LONG).show();
            return;
        }
        Toast.makeText(context,"requesting interstitial",Toast.LENGTH_LONG).show();

        loading = true;
        AdRequest adRequest = new AdRequest.Builder().build();

        InterstitialAd.load(context, "Interstial Ad Unit ID", adRequest, new InterstitialAdLoadCallback() {
            @Override
            public void onAdLoaded(@NonNull InterstitialAd interstitialAd) {
                mInterstitialAd = interstitialAd;
                Toast.makeText(finalContext,"ad loaded",Toast.LENGTH_LONG).show();
                loading = false;
            }

            @Override
            public void onAdFailedToLoad(@NonNull LoadAdError loadAdError) {
                mInterstitialAd = null;
                loading = false;
                Toast.makeText(finalContext,"ad failed to load",Toast.LENGTH_LONG).show();
            }

        });
    }

    public static void showInterstitial(Activity activity, @NonNull AdListener listener) {
        
        if (showing) {
            Toast.makeText(activity,"already showing",Toast.LENGTH_LONG).show();
            listener.onCompleted();
            return;
        }

        if (mInterstitialAd != null) {
            showNow(activity, listener);

        } else {
            Toast.makeText(activity,"mInterstitialAd is null",Toast.LENGTH_LONG).show();
            listener.onCompleted();
            loadInterstitial(activity.getApplicationContext());
        }

    }

    private static void showNow(Activity activity, AdListener listener) {

        if (mInterstitialAd != null && !showing) {
            showing = true;
            mInterstitialAd.setFullScreenContentCallback(new FullScreenContentCallback() {
                @Override
                public void onAdDismissedFullScreenContent() {
                    Toast.makeText(activity,"Ad dismissed",Toast.LENGTH_LONG).show();
                    mInterstitialAd = null;
                    listener.onCompleted();
                    showing = false;
                    // times to load an new interstitial ad content
                    loadInterstitial(activity.getApplicationContext());
                }

                @Override
                public void onAdFailedToShowFullScreenContent(@NonNull AdError adError) {
                    Toast.makeText(activity,"AdFailedToShowFullScreenContent",Toast.LENGTH_LONG).show();
                    mInterstitialAd = null;
                    listener.onCompleted();
                    showing = false;

                    // times to load an new interstitial ad content
                    loadInterstitial(activity.getApplicationContext());
                }


            });
            //  Now show the ad
            Toast.makeText(activity,"call to show ad",Toast.LENGTH_LONG).show();
            mInterstitialAd.show(activity);
        } else {
            Toast.makeText(activity,"either mInterstitialAd is null or ad already is showing",Toast.LENGTH_LONG).show();
            listener.onCompleted();
        }
    }

        public interface AdListener {
        void onCompleted();
    }

}

Please help.

The delay problem

You can't really help it. The problem is from the admob. This will happen. But, to know more about it, we can post an issue about that on the Google Issue Tracker.

The button problem

I dont think this is any hard task. Just follow the steps:

1. Create a ProgressBar in your xml layout on top of the button and set its visibility to gone

2. When the button is click and the ad is shown, you can set the button to invisible and the progress bar can be set to visible.

3. Then after a delay, the other activity opens without any harm to the activity from NullPointerException