Adiciona barra de busca em qualquer versão do IOS

UIViewController+AdicionarBarraDeBusca.cs

using System;
using App.iOS.Utils;
using UIKit;

namespace App.iOS.Extensions
{
    //https://stackoverflow.com/questions/48007690/issue-with-uisearchcontroller-in-uitableview-on-ios-11
    //https://stackoverflow.com/questions/28326269/uisearchbar-presented-by-uisearchcontroller-in-table-header-view-animates-too-fa?rq=1
    public static class UIViewController_AdicionarBarraDeBusca
    {
        public static UISearchController AdicionarBarraDeBusca(this UIViewController @this)
        {
            if (VersaoIosSuportaBarraDeBuscaNoNavigationItem)
                return AdicionarBarraDeBuscaAoNavigationItem(@this);

            return AdicionarBarraDeBuscaDoJeitoObsoleto(@this);
        }

        private static bool VersaoIosSuportaBarraDeBuscaNoNavigationItem => UIDevice.CurrentDevice.CheckSystemVersion(11, 0);

        private static UISearchController AdicionarBarraDeBuscaAoNavigationItem(UIViewController @this)
        {
            var searchController = new UISearchController(null as UIViewController);
            searchController.SearchResultsUpdater = @this as IUISearchResultsUpdating ?? 
                                                    throw new ControllerNaoImplementaBarraDeBuscaException(@this);
            searchController.ObscuresBackgroundDuringPresentation = false;
            searchController.SearchBar.Placeholder = "Buscar";
            @this.NavigationItem.SearchController = searchController;
            @this.NavigationItem.HidesSearchBarWhenScrolling = false;
            @this.DefinesPresentationContext = true;

            return searchController;
        }

        private static UISearchController AdicionarBarraDeBuscaDoJeitoObsoleto(UIViewController @this)
        {
            var searchController = new UISearchController(null as UIViewController);
            searchController.SearchResultsUpdater = @this as IUISearchResultsUpdating ?? 
                                                    throw new ControllerNaoImplementaBarraDeBuscaException(@this);
            searchController.HidesNavigationBarDuringPresentation = true;
            searchController.DimsBackgroundDuringPresentation = false;
            searchController.SearchBar.Placeholder = "Buscar";

            if (@this is UITableViewController tableView)
                AdicionaBarraDeBuscaAoTableHeaderView(tableView, searchController);
            else
                AdicionaBarraDeBuscaAoTitleView(@this, searchController);
            
            @this.DefinesPresentationContext = true;
            @this.ExtendedLayoutIncludesOpaqueBars = true;
            
            return searchController;
        }

        private static void AdicionaBarraDeBuscaAoTitleView(UIViewController @this, UISearchController searchController) => @this.NavigationItem.TitleView = searchController.SearchBar;

        private static void AdicionaBarraDeBuscaAoTableHeaderView(UITableViewController tableView,
            UISearchController searchController) => 
            tableView.TableView.AtribuirTableHeaderView(searchController.SearchBar);

        private class ControllerNaoImplementaBarraDeBuscaException : Exception
        {
            public ControllerNaoImplementaBarraDeBuscaException(UIViewController controller) : 
                base ($"Controller {controller.GetType().Name} deve implementar interface {nameof(IUISearchResultsUpdating)}")
            {}
        }
    }
}