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To achieve Secure Background Screen in Xamarin, you do not need to use sleep method.

For android. Open your MainActivity.cs add Window.SetFlags(WindowManagerFlags.Secure, WindowManagerFlags.Secure); in your OnCreate() method.

public class MainActivity : global::Xamarin.Forms.Platform.Android.FormsAppCompatActivity
    {
        protected override void OnCreate(Bundle savedInstanceState)
        {
            base.OnCreate(savedInstanceState);

            Xamarin.Essentials.Platform.Init(this, savedInstanceState);
            global::Xamarin.Forms.Forms.Init(this, savedInstanceState);
            LoadApplication(new App());
            Window.SetFlags(WindowManagerFlags.Secure, WindowManagerFlags.Secure);
        }

For iOS. The easiest is to set a blur when the AppDelegate calls OnResignActivation. Place the following in your AppDelegate of your Xamarin.iOS app. This creates a blur effect on the main window, when OnResignActivation is called, then removes it, when OnActivated is called.

UIVisualEffectView _blurWindow = null;

public override void OnActivated(UIApplication application)
{
    base.OnActivated(application);

    _blurWindow?.RemoveFromSuperview();
    _blurWindow?.Dispose();
    _blurWindow = null;
}

public override void OnResignActivation(UIApplication application)
{
    base.OnResignActivation(application);

    using (var blurEffect = UIBlurEffect.FromStyle(UIBlurEffectStyle.Dark))
    {
        _blurWindow = new UIVisualEffectView(blurEffect)
        {
            Frame = UIApplication.SharedApplication.KeyWindow.RootViewController.View.Bounds
        };
        UIApplication.SharedApplication.KeyWindow.RootViewController.View.AddSubview(_blurWindow);
     }
}

Here is a blog about it.

======================Update==============================

For IOS, I found we can custom this view, For example. we can add an icon to the Secure Background Screen. I Add a image to the UIVisualEffectView

public override void OnActivated(UIApplication application)
        {
            base.OnActivated(application);

            _blurWindow?.RemoveFromSuperview();
            _blurWindow?.Dispose();
            _blurWindow = null;
        }

        public override void OnResignActivation(UIApplication application)
        {
            base.OnResignActivation(application);

            using (var blurEffect = UIBlurEffect.FromStyle(UIBlurEffectStyle.Dark))
            {
                _blurWindow = new UIVisualEffectView(blurEffect)
                {
                    Frame = UIApplication.SharedApplication.KeyWindow.RootViewController.View.Bounds
                };

                UIImageView image = new UIImageView();
                image.Frame = new CoreGraphics.CGRect(100, 100, 40, 40);
                image.Image = UIImage.FromFile("icon.png");
                _blurWindow.ContentView.Add(image);
                UIApplication.SharedApplication.KeyWindow.RootViewController.View.AddSubview(_blurWindow);
            }
        }

Here is running screenshot.

Best Regards,

Leon Lu

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