Sample: BTProgressHUD blocking tab bar

AppDelegate.cs

using System;
using Foundation;
using UIKit;
using CoreGraphics;
using BigTed;
using System.Threading.Tasks;
using System.Linq;
using ObjCRuntime;

namespace HudOverTabsSample {
    public class NumberedTabViewController : UIViewController {
        readonly int tabNumber;
        public NumberedTabViewController(int tabNumber) {
            this.tabNumber = tabNumber;
        }
        UITextView someView;
        bool hasAdjustedForTopLayoutGuide = false;
        public override void ViewDidLayoutSubviews() {
            base.ViewDidLayoutSubviews();
            if (!hasAdjustedForTopLayoutGuide && UIDevice.CurrentDevice.CheckSystemVersion(7, 0)) {
                View.Subviews.ToList().ForEach(v => v.Center = new CGPoint(v.Center.X, v.Center.Y + TopLayoutGuide.Length));
            }
            hasAdjustedForTopLayoutGuide = true;
        }
        public override void ViewDidLoad() {
            base.ViewDidLoad();
            View.BackgroundColor = UIColor.White;
            someView = new UITextView() {
                BackgroundColor = UIColor.LightGray,
                Text = string.Format("Tab {0} Content", tabNumber),
            };
            someView.Frame = new CGRect(new CGPoint(6f, 6f), new CGSize(View.Bounds.Width - 12f, 50f));
            View.Add(someView);
        }
        public override void ViewDidAppear(bool animated) {
            base.ViewDidAppear(animated);
            var hud = ShowHud("Oh hai");
            Task.Delay(3000).ContinueWith((task) => {
                InvokeOnMainThread(() => {
                    hud.Dismiss();
                });
            });
        }
        ProgressHUD ShowHud(string text) {
            // Need discrete HUDs so one tab won't try to hide anothers pending HUD.
            var hud = new ProgressHUD();
            hud.Show(status: "Oh hai", maskType: ProgressHUD.MaskType.Gradient);
            return hud;
        }
    }

    [Register("AppDelegate")]
    public partial class AppDelegate : UIApplicationDelegate {
        public override UIWindow Window { get; set; }
        UITabBarController rootController;
        public override bool FinishedLaunching(UIApplication app, NSDictionary options) {
            var tabImage = UIImage.FromBundle("star");
            rootController = new UITabBarController() {
                ViewControllers = Enumerable.Range(0, 4).Select(i => {
                    var tabBarItem = new UITabBarItem(i.ToString(), tabImage, tabImage);
                    return new NumberedTabViewController(i) { TabBarItem = tabBarItem };
                }).ToArray(),
            };

            Window = new UIWindow(UIScreen.MainScreen.Bounds);
            Window.RootViewController = rootController;
            Window.MakeKeyAndVisible();
            return true;
        }
    }

    public class Application {
        static void Main(string[] args) {
            AppDomain.CurrentDomain.UnhandledException += OnUnhandledException;

            try {
                UIApplication.Main(args, null, "AppDelegate");
            }
            catch (Exception ex) {
                HandleException(ex);
            }
        }
        static void OnUnhandledException(object sender, UnhandledExceptionEventArgs e) {
            HandleException(e.ExceptionObject as Exception);
        }
        static void HandleException(Exception exception) {
            Console.WriteLine("Top-level exception: {0}", exception);
        }
    }
}