ActivityLifecycleCallbacksHelper to get TopActivity from anywhere

ActivityLifecycleHelper.cs

    public sealed class ActivityLifecycleHelper : IDisposable
    {
        private readonly ActivityLifecycleCallbacksHelper activityLifecycle = new ActivityLifecycleCallbacksHelper();
        private Android.App.Application application;

        public Activity TopActivity { get; private set; }

        public ActivityLifecycleHelper(Android.App.Application application)
        {
            this.application = application;
            application.RegisterActivityLifecycleCallbacks(activityLifecycle);

            activityLifecycle.ActivityResumed += (sender, args) => TopActivity = args.Activity;
            activityLifecycle.ActivityPaused += (sender, args) => TopActivity = null;
            activityLifecycle.ActivityDestroyed += (sender, args) => TopActivity = null;
        }

        public void Dispose()
        {
            application.UnregisterActivityLifecycleCallbacks(activityLifecycle);
            TopActivity = null;
            application = null;
        }
    }
    
    public class ActivityLifecycleEventArgs : EventArgs
    {
        public Activity Activity { get; }
        public Bundle State { get; }

        public ActivityLifecycleEventArgs(Activity activity, Bundle state = null)
        {
            Activity = activity;
            State = state;
        }
    }

    public class ActivityLifecycleCallbacksHelper : Java.Lang.Object, Application.IActivityLifecycleCallbacks
    {
        public event EventHandler<ActivityLifecycleEventArgs> ActivityCreated;
        public event EventHandler<ActivityLifecycleEventArgs> ActivityDestroyed;
        public event EventHandler<ActivityLifecycleEventArgs> ActivityPaused;
        public event EventHandler<ActivityLifecycleEventArgs> ActivityResumed;
        public event EventHandler<ActivityLifecycleEventArgs> ActivitySaveInstanceState;
        public event EventHandler<ActivityLifecycleEventArgs> ActivityStarted;
        public event EventHandler<ActivityLifecycleEventArgs> ActivityStopped;

        public void OnActivityCreated(Activity activity, Bundle savedInstanceState)
        {
            ActivityCreated?.Invoke(this, new ActivityLifecycleEventArgs(activity, savedInstanceState));
        }

        public void OnActivityDestroyed(Activity activity)
        {
            ActivityCreated?.Invoke(this, new ActivityLifecycleEventArgs(activity));
        }

        public void OnActivityPaused(Activity activity)
        {
            ActivityCreated?.Invoke(this, new ActivityLifecycleEventArgs(activity));
        }

        public void OnActivityResumed(Activity activity)
        {
            ActivityCreated?.Invoke(this, new ActivityLifecycleEventArgs(activity));
        }

        public void OnActivitySaveInstanceState(Activity activity, Bundle outState)
        {
            ActivityCreated?.Invoke(this, new ActivityLifecycleEventArgs(activity, outState));
        }

        public void OnActivityStarted(Activity activity)
        {
            ActivityCreated?.Invoke(this, new ActivityLifecycleEventArgs(activity));
        }

        public void OnActivityStopped(Activity activity)
        {
            ActivityCreated?.Invoke(this, new ActivityLifecycleEventArgs(activity));
        }
    }