MonoGame_AdMobCrash_Workaround_MainActivity.cs

using Android.App;
using Android.Content;
using Android.Gms.Ads;
using Android.OS;
using Android.Widget;
using System;

namespace AdMobTest_MonoGame
{
    [Activity(Label = "MainActivity"
        , MainLauncher = true
        , LaunchMode = Android.Content.PM.LaunchMode.SingleInstance
        )]
    public class MainActivity : Activity
    {
        private bool _firstResume = true;

        protected override void OnCreate(Bundle savedInstanceState)
        {
            base.OnCreate(savedInstanceState);

            AdManager.Initialize(this);
            AdManager.AdClosed += (sender, e) => ShowGameActivity();

            // Create your application here
            LinearLayout layout = new LinearLayout(this);
            layout.Orientation = Orientation.Vertical;

            layout.AddView(
                new TextView(this)
                {
                    Text = "This is a temporary launcher to handle ad stuff... :)"
                }
            );

            this.SetContentView(layout);
        }

        protected override void OnResume()
        {
            base.OnResume();

            if (_firstResume)
            {
                _firstResume = false;
                ShowGameActivity();
            }
            else
            {
                AdManager.ShowAd();
            }
        }

        private void ShowGameActivity()
        {
            Intent showGameIntent = new Intent(this, typeof(Activity1));
            this.StartActivity(showGameIntent);
        }
    }

    public static class AdManager
    {
        private static InterstitialAd _ad = null;

        public static bool AdReady { get; private set; } = false;
        public static event EventHandler<EventArgs> AdClosed;

        public static void Initialize(Context context)
        {
            if (_ad != null)
            {
                if (_ad.AdListener != null)
                    _ad.AdListener.Dispose();
                _ad.Dispose();
            }

            _ad = new InterstitialAd(context);
            _ad.AdUnitId = "<< your ad unit id here >>";

            MyAdListener listener = new MyAdListener();
            listener.AdLoaded += (sender, e) => AdReady = true;
            listener.AdClosed +=
                (sender, e) =>
                {
                    RequestAd();

                    if (AdClosed != null)
                        AdClosed(null, e);
                };

            _ad.AdListener = listener;

            RequestAd();
        }

        public static void ShowAd()
        {
            if (_ad.IsLoaded == true)
                _ad.Show();
        }

        private static void RequestAd()
        {
            AdReady = false;
            AdRequest.Builder builder = new AdRequest.Builder();
            builder.AddTestDevice(AdRequest.DeviceIdEmulator);
            AdRequest request = builder.Build();
            _ad.LoadAd(request);
        }
    }

    public class MyAdListener : AdListener
    {
        public event EventHandler AdLoaded;
        public event EventHandler AdClosed;

        public override void OnAdLoaded()
        {
            base.OnAdLoaded();

            if (this.AdLoaded != null)
                this.AdLoaded(this, new EventArgs());
        }

        public override void OnAdClosed()
        {
            base.OnAdClosed();

            if (this.AdClosed != null)
                this.AdClosed(this, new EventArgs());
        }
    }
}