Modified BrowseViewController

BrowseViewController.cs

using System;
using System.Collections.Specialized;

using Foundation;
using UIKit;
using System.Threading.Tasks;
using MasterDetail.ViewModel;

namespace MasterDetail.iOS
{
    public partial class BrowseViewController : UITableViewController
    {
		UIRefreshControl refreshControl;

		public ItemsViewModel ViewModel { get; set; }

		public BrowseViewController(IntPtr handle) : base(handle) 
		{ 
			ViewModel = new ItemsViewModel();
		}

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

			// Setup UITableView.
			refreshControl = new UIRefreshControl();
			refreshControl.ValueChanged += RefreshControl_ValueChanged;
			TableView.Add(refreshControl);
			TableView.Source = new ItemsDataSource(ViewModel);

			Title = ViewModel.Title;

			ViewModel.PropertyChanged += IsBusy_PropertyChanged;
			ViewModel.Items.CollectionChanged += Items_CollectionChanged;

		}
        public override async void ViewDidAppear(bool animated)
        {
            base.ViewDidAppear(animated);

            if (ViewModel.Items.Count == 0)
                await ViewModel.ExecuteLoadItemsCommand();
        }

        public override void PrepareForSegue(UIStoryboardSegue segue, NSObject sender)
		{
			if (segue.Identifier == "NavigateToItemDetailSegue")
			{
				var controller = segue.DestinationViewController as BrowseItemDetailViewController;
				var indexPath = TableView.IndexPathForCell(sender as UITableViewCell);
				var item = ViewModel.Items[indexPath.Row];

				controller.ViewModel = new ItemDetailViewModel(item);
			}
		}

		async void RefreshControl_ValueChanged(object sender, EventArgs e)
		{
            if (!ViewModel.IsBusy && refreshControl.Refreshing)
                await ViewModel.ExecuteLoadItemsCommand();

        }

		void IsBusy_PropertyChanged(object sender, System.ComponentModel.PropertyChangedEventArgs e)
		{
			var propertyName = e.PropertyName;
			switch (propertyName)
			{
				case nameof(ViewModel.IsBusy):
					{
						InvokeOnMainThread(() =>
						{
							if (ViewModel.IsBusy && !refreshControl.Refreshing)
								refreshControl.BeginRefreshing();
							else if (!ViewModel.IsBusy)
								refreshControl.EndRefreshing();
						});
					}
					break;
			}
		}

		void Items_CollectionChanged(object sender, NotifyCollectionChangedEventArgs e)
		{
			InvokeOnMainThread(() => TableView.ReloadData());
		}

		[Action("UnwindToBrowse:")]
		public void UnwindToBrowse (UIStoryboardSegue segue)
		{
		    Console.WriteLine("UNwound");
		}
	}

	class ItemsDataSource : UITableViewSource
	{
		static readonly NSString CELL_IDENTIFIER = new NSString("ITEM_CELL");

        ItemsViewModel viewModel;

		public ItemsDataSource(ItemsViewModel viewModel)
		{
			this.viewModel = viewModel;
		}

		public override nint RowsInSection(UITableView tableview, nint section) => viewModel.Items.Count;
		public override nint NumberOfSections(UITableView tableView) => 1;

		public override UITableViewCell GetCell(UITableView tableView, NSIndexPath indexPath)
		{
			var cell = tableView.DequeueReusableCell(CELL_IDENTIFIER, indexPath);

			var item = viewModel.Items[indexPath.Row];
			cell.TextLabel.Text = item.Text;
			cell.DetailTextLabel.Text = item.Description;
			cell.LayoutMargins = UIEdgeInsets.Zero;

			return cell;
		}
	}
}