Preserving SWTableViewCell UI state

gistfile1.cs

using System;
using Foundation;
using UIKit;
using System.Collections.Generic;
using SWTableViewCell;
using System.Linq;

namespace TestNamespace
{
	public partial class TestViewController : UITableViewController
	{
		public SWTVC_testViewController (IntPtr handle)
			: base (handle)
		{
		}

		ViewDataSource dataSource;

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

			NavigationItem.RightBarButtonItem = new UIBarButtonItem (UIBarButtonSystemItem.Refresh, delegate {
				TableView.ReloadData ();
			});

			dataSource = new ViewDataSource ();
			TableView.DataSource = dataSource;
		}
	}

	// the data that we want in the table
	public class ViewDataSource : UITableViewDataSource
	{
		readonly List<CellViewModel> testArray;

		public ViewDataSource ()
		{
			testArray = Enumerable
				.Range (1, 100)
				.Select (i => new CellViewModel(i))
				.ToList ();
		}

		public override UITableViewCell GetCell (UITableView tableView, NSIndexPath indexPath)
		{
			return MemoryTableViewCell.GetCell (tableView, testArray [indexPath.Row]);
		}

		public override nint RowsInSection (UITableView tableView, nint section)
		{
			return testArray.Count;
		}
	}

	// the cell holds the logic that maps the data and state between the cell
	public class MemoryTableViewCell : SWTableViewCell.SWTableViewCell, ISWTableViewCellDelegate
	{
		CellViewModel viewModel;
		bool isPreparing;

		public MemoryTableViewCell (UITableViewCellStyle style, string id)
			: base (style, id)
		{
		}

		// mark the cell as invalid
		public override void PrepareForReuse ()
		{
			// we need to do this as this method resets the scroll offset
			isPreparing = true;

			base.PrepareForReuse ();
		}

		// when the cell item is scrolled left or right
		[Export ("swipeableTableViewCell:scrollingToState:")]
		public virtual void ScrollingToState (SWTableViewCell.SWTableViewCell cell, SWCellState state)
		{
			// only update once the cell is visible
			if (!isPreparing) {
				viewModel.State = state;
			}
		}

		// logic to create and update a cell
		public static MemoryTableViewCell GetCell (UITableView tableView, CellViewModel viewModel)
		{
			// see if there is an old cell
			var cell = (MemoryTableViewCell)tableView.DequeueReusableCell ("cellIdentifier");

			// create a brand new cell
			if (cell == null) {
				// the buttons
				var rightUtilityButtons = new NSMutableArray ();
				rightUtilityButtons.AddUtilityButton (UIColor.FromRGBA (0.78f, 0.78f, 0.8f, 1.0f), "More");
				rightUtilityButtons.AddUtilityButton (UIColor.FromRGBA (1.0f, 0.231f, 0.188f, 1.0f), "Delete");
				var buttons = NSArray.FromArray<UIButton> (rightUtilityButtons);

				// the cell
				cell = new MemoryTableViewCell (UITableViewCellStyle.Default, "cellIdentifier");
				cell.RightUtilityButtons = buttons;
				cell.WeakDelegate = cell;
			}

			// so that we can save the item state
			cell.viewModel = viewModel;

			// update the cell visuals
			cell.TextLabel.Text = viewModel.Value;

			// restore view state
			if (viewModel.State == SWCellState.Right)
				cell.ShowRightUtilityButtons (false);

			cell.isPreparing = false;

			return cell;
		}
	}

	// the view model holds the data as well as any UI state
	public class CellViewModel
	{
		public CellViewModel (int item)
		{
			Value = string.Format ("Item {0}...", item);
			State = SWCellState.Center;
		}

		public string Value{ get; set; }

		public SWCellState State{ get; set; }
	}
}