context: // 
  // ListViewBackend.cs
  //  
  // Author:
  //       Lluis Sanchez <lluis@xamarin.com>
  //       Jan Strnadek <jan.strnadek@gmail.com>
  //              - GetAtRowPosition
  //              - NSTableView for mouse events
  // 
  // Copyright (c) 2011 Xamarin Inc
  // 
  // Permission is hereby granted, free of charge, to any person obtaining a copy
  // of this software and associated documentation files (the "Software"), to deal
  // in the Software without restriction, including without limitation the rights
  // to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
  // copies of the Software, and to permit persons to whom the Software is
  // furnished to do so, subject to the following conditions:
  // 
  // The above copyright notice and this permission notice shall be included in
  // all copies or substantial portions of the Software.
  // 
  // THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  // IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  // FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
  // AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  // LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
  // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
  // THE SOFTWARE.
  
  using System;
  using System.Collections.Generic;
  using System.Linq;
  using AppKit;
  using CoreGraphics;
  using Foundation;
  using Xwt.Backends;
  
  namespace Xwt.Mac
  {
  	public class ListViewBackend: TableViewBackend<NSTableView, IListViewEventSink>, IListViewBackend
  	{
  		class ListDelegate: NSTableViewDelegate
  		{
  			public ListViewBackend Backend;
  			
  			public override nfloat GetRowHeight (NSTableView tableView, nint row)
  			{
  				// GetView() and GetRowView() can't be used here, hence we use cached
  				// sizes calculated by the backend or calcuate the height using the template view
  				nfloat height = Backend.RowHeights[(int)row];
  				if (height <= -1)
  					height = Backend.RowHeights [(int)row] = Backend.CalcRowHeight (row, false);
  				return height;
  			}
  
  			public override NSTableRowView CoreGetRowView (NSTableView tableView, nint row)
  			{
  				return tableView.GetRowView (row, false) ?? new TableRowView ();
  			}
  
  			public override NSView GetViewForItem (NSTableView tableView, NSTableColumn tableColumn, nint row)
  			{
  				var col = tableColumn as TableColumn;
  				var cell = tableView.MakeView (tableColumn.Identifier, this) as CompositeCell;
  				if (cell == null)
  					cell = col.CreateNewView ();
  				cell.ObjectValue = NSNumber.FromNInt (row);
  				return cell;
  			}
  
  			public override nfloat GetSizeToFitColumnWidth (NSTableView tableView, nint column)
  			{
  				var tableColumn = Backend.Columns[(int)column] as TableColumn;
  				var width = tableColumn.HeaderCell.CellSize.Width;
  
  				CompositeCell templateCell = null;
  				for (int i = 0; i < tableView.RowCount; i++) {
  					var cellView = tableView.GetView (column, i, false) as CompositeCell;
  					if (cellView == null) { // use template for invisible rows
  						cellView = templateCell ?? (templateCell = (tableColumn as TableColumn)?.DataView?.Copy () as CompositeCell);
  						if (cellView != null)
  							cellView.ObjectValue = NSNumber.FromInt32 (i);
  					}
  					width = (nfloat)Math.Max (width, cellView.FittingSize.Width);
  				}
  				return width;
  			}
  
  			public override NSIndexSet GetSelectionIndexes(NSTableView tableView, NSIndexSet proposedSelectionIndexes)
  			{
  				return Backend.SelectionMode != SelectionMode.None ? proposedSelectionIndexes : new NSIndexSet();
  			}
  		}
  
  		IListDataSource source;
  		ListSource tsource;
  
  		protected override NSTableView CreateView ()
  		{
  			var listView = new NSTableViewBackend (this);
  			listView.Delegate = new ListDelegate { Backend = this };
  			return listView;
  		}
  
  		protected override string SelectionChangeEventName {
  			get { return "NSTableViewSelectionDidChangeNotification"; }
  		}
  
  		public override void EnableEvent (object eventId)
  		{
  			base.EnableEvent (eventId);
  			if (eventId is ListViewEvent) {
  				switch ((ListViewEvent)eventId) {
  				case ListViewEvent.RowActivated:
  					Table.DoubleClick += HandleDoubleClick;
  					break;
  				}
  			}
  		}
  
  		public override void DisableEvent (object eventId)
  		{
  			base.DisableEvent (eventId);
  			if (eventId is ListViewEvent) {
  				switch ((ListViewEvent)eventId) {
  				case ListViewEvent.RowActivated:
  					Table.DoubleClick -= HandleDoubleClick;
  					Table.DoubleAction = null;
  					break;
  				}
  			}
  		}
  
  		void HandleDoubleClick (object sender, EventArgs e)
  		{
  			var cr = Table.ClickedRow;
  			if (cr >= 0) {
  				ApplicationContext.InvokeUserCode (delegate {
  					((IListViewEventSink)EventSink).OnRowActivated ((int)cr);
  				});
  			}
  		}
  		
  		public virtual void SetSource (IListDataSource source, IBackend sourceBackend)
  		{
  			this.source = source;
  
  			RowHeights = new List<nfloat> ();
  			for (int i = 0; i < source.RowCount; i++)
  				RowHeights.Add (-1);
  
  			tsource = new ListSource (source);
  			Table.DataSource = tsource;
  
  			//TODO: Reloading single rows would be slightly more efficient.
  			//      According to NSTableView.ReloadData() documentation,
  			//      only the visible rows are reloaded.
  			source.RowInserted += (sender, e) => {
  				RowHeights.Insert (e.Row, -1);
  				Table.ReloadData ();
  			};
  			source.RowDeleted += (sender, e) => {
  				RowHeights.RemoveAt (e.Row);
  				Table.ReloadData ();
  			};
  			source.RowChanged += (sender, e) => {
  				UpdateRowHeight (e.Row);
  				Table.ReloadData (NSIndexSet.FromIndex (e.Row), NSIndexSet.FromNSRange (new NSRange (0, Table.ColumnCount)));
  			};
  			source.RowsReordered += (sender, e) => { RowHeights.Clear (); Table.ReloadData (); };
  		}
  
  		public override void InvalidateRowHeight (object pos)
  		{
  			UpdateRowHeight((int)pos);
  		}
  		
  		List<nfloat> RowHeights = new List<nfloat> ();
  		bool updatingRowHeight;
  		public void UpdateRowHeight (nint row)
  		{
  			if (updatingRowHeight)
  				return;
  			RowHeights[(int)row] = CalcRowHeight (row);
  			Table.NoteHeightOfRowsWithIndexesChanged (NSIndexSet.FromIndex (row));
  		}
  
  		nfloat CalcRowHeight (nint row, bool tryReuse = true)
  		{
  			updatingRowHeight = true;
  			var height = Table.RowHeight;
  
  			for (int i = 0; i < Columns.Count; i++) {
  				CompositeCell cell = tryReuse ? Table.GetView (i, row, false) as CompositeCell : null;
  				if (cell == null) {
  					cell = (Columns [i] as TableColumn)?.DataView as CompositeCell;
  					cell.ObjectValue = NSNumber.FromNInt (row);
  					height = (nfloat)Math.Max (height, cell.FittingSize.Height);
  				} else {
  					height = (nfloat)Math.Max (height, cell.GetRequiredHeightForWidth (cell.Frame.Width));
  				}
  			}
  			updatingRowHeight = false;
  			return height;
  		}
  		
  		public int[] SelectedRows {
  			get {
  				int[] sel = new int [Table.SelectedRowCount];
  				if (sel.Length > 0) {
  					int i = 0;
  					foreach (int r in Table.SelectedRows)
  
gt: 						sel [i++] = r;