Add iOS prototypical cell cache for LV RowHeight calcs (#1143)

17 files changed, 344 insertions, 89 deletions

diff --git a/Xamarin.Forms.Core.UnitTests/DataTemplateSelectorTests.cs b/Xamarin.Forms.Core.UnitTests/DataTemplateSelectorTests.cs
index 552f784b..d009a608 100644
--- a/Xamarin.Forms.Core.UnitTests/DataTemplateSelectorTests.cs
+++ b/Xamarin.Forms.Core.UnitTests/DataTemplateSelectorTests.cs
@@ -90,4 +90,69 @@ namespace Xamarin.Forms.Core.UnitTests
 			Assert.Throws<NotSupportedException> (() => dts.SelectTemplate ((byte)0, null));
 		}
 	}
+
+	[TestFixture]
+	public class DataTemplateRecycleTests : BaseTestFixture
+	{
+		[TearDown]
+		public override void TearDown()
+		{
+			base.TearDown();
+			Device.PlatformServices = null;
+		}
+
+		[SetUp]
+		public override void Setup()
+		{
+			base.Setup();
+			Device.PlatformServices = new MockPlatformServices();
+		}
+
+		class TestDataTemplateSelector : DataTemplateSelector
+		{
+			readonly DataTemplate declarativeTemplate;
+			readonly DataTemplate proceduralTemplate;
+
+			public TestDataTemplateSelector ()
+			{
+				declarativeTemplate = new DataTemplate(typeof(ViewCell));
+				proceduralTemplate = new DataTemplate(() => new EntryCell());
+			}
+
+			protected override DataTemplate OnSelectTemplate(object item, BindableObject container)
+			{
+				Counter++;
+
+				if (item is string)
+					return declarativeTemplate;
+
+				return proceduralTemplate;
+			}
+
+			public int Counter = 0;
+		}
+
+		[Test]
+		public void ListViewSupport ()
+		{
+			var listView = new ListView(ListViewCachingStrategy.RecycleElementAndDataTemplate);
+			listView.ItemsSource = new object[] { "foo", "bar", 0 };
+
+			Assert.That(listView.CachingStrategy == 
+				ListViewCachingStrategy.RecycleElementAndDataTemplate);
+
+			var selector = new TestDataTemplateSelector();
+			listView.ItemTemplate = selector;
+			Assert.That(selector.Counter == 0);
+
+			Assert.IsInstanceOf<ViewCell>(listView.TemplatedItems[0]);
+			Assert.That(selector.Counter == 1);
+
+			Assert.IsInstanceOf<ViewCell>(listView.TemplatedItems[1]);
+			Assert.That(selector.Counter == 1);
+
+			Assert.Throws<NotSupportedException>(
+				() => { var o = listView.TemplatedItems[2]; });
+		}
+	}
 }
\ No newline at end of file
diff --git a/Xamarin.Forms.Core/DataTemplateExtensions.cs b/Xamarin.Forms.Core/DataTemplateExtensions.cs
index 3589fb01..34ee5941 100644
--- a/Xamarin.Forms.Core/DataTemplateExtensions.cs
+++ b/Xamarin.Forms.Core/DataTemplateExtensions.cs
@@ -5,14 +5,18 @@ namespace Xamarin.Forms.Internals
 	[EditorBrowsable(EditorBrowsableState.Never)]
 	public static class DataTemplateExtensions
 	{
-		public static object CreateContent(this DataTemplate self, object item, BindableObject container)
+		public static DataTemplate SelectDataTemplate(this DataTemplate self, object item, BindableObject container)
 		{
 			var selector = self as DataTemplateSelector;
-			if (selector != null)
-			{
-				self = selector.SelectTemplate(item, container);
-			}
-			return self.CreateContent();
+			if (selector == null)
+				return self;
+
+			return selector.SelectTemplate(item, container);
+		}
+
+		public static object CreateContent(this DataTemplate self, object item, BindableObject container)
+		{
+			return self.SelectDataTemplate(item, container).CreateContent();
 		}
 	}
 }
\ No newline at end of file
diff --git a/Xamarin.Forms.Core/DataTemplateSelector.cs b/Xamarin.Forms.Core/DataTemplateSelector.cs
index 8ffa4781..7e284f7c 100644
--- a/Xamarin.Forms.Core/DataTemplateSelector.cs
+++ b/Xamarin.Forms.Core/DataTemplateSelector.cs
@@ -1,15 +1,39 @@
 using System;
+using System.Collections.Generic;
 
 namespace Xamarin.Forms
 {
 	public abstract class DataTemplateSelector : DataTemplate
 	{
+		Dictionary<Type, DataTemplate> _dataTemplates = new Dictionary<Type, DataTemplate>();
+
 		public DataTemplate SelectTemplate(object item, BindableObject container)
 		{
-			DataTemplate result = OnSelectTemplate(item, container);
-			if (result is DataTemplateSelector)
-				throw new NotSupportedException("DataTemplateSelector.OnSelectTemplate must not return another DataTemplateSelector");
-			return result;
+			var listView = container as ListView;
+
+			var recycle = listView == null ? false :
+				(listView.CachingStrategy & ListViewCachingStrategy.RecycleElementAndDataTemplate) ==
+					ListViewCachingStrategy.RecycleElementAndDataTemplate;
+
+			DataTemplate dataTemplate = null;
+			if (recycle && _dataTemplates.TryGetValue(item.GetType(), out dataTemplate))
+				return dataTemplate;
+
+			dataTemplate = OnSelectTemplate(item, container);
+			if (dataTemplate is DataTemplateSelector)
+				throw new NotSupportedException(
+					"DataTemplateSelector.OnSelectTemplate must not return another DataTemplateSelector");
+
+			if (recycle)
+			{
+				if (!dataTemplate.CanRecycle)
+					throw new NotSupportedException(
+						"RecycleElementAndDataTemplate requires DataTemplate activated with ctor taking a type.");
+
+				_dataTemplates[item.GetType()] = dataTemplate;
+			}
+
+			return dataTemplate;
 		}
 
 		protected abstract DataTemplate OnSelectTemplate(object item, BindableObject container);
diff --git a/Xamarin.Forms.Core/ElementTemplate.cs b/Xamarin.Forms.Core/ElementTemplate.cs
index 016dee7e..d7e842b5 100644
--- a/Xamarin.Forms.Core/ElementTemplate.cs
+++ b/Xamarin.Forms.Core/ElementTemplate.cs
@@ -10,6 +10,7 @@ namespace Xamarin.Forms
 	{
 		List<Action<object, ResourcesChangedEventArgs>> _changeHandlers;
 		Element _parent;
+		bool _canRecycle; // aka IsDeclarative
 
 		internal ElementTemplate()
 		{
@@ -20,6 +21,8 @@ namespace Xamarin.Forms
 			if (type == null)
 				throw new ArgumentNullException("type");
 
+			_canRecycle = true;
+
 			LoadTemplate = () => Activator.CreateInstance(type);
 		}
 
@@ -46,6 +49,7 @@ namespace Xamarin.Forms
 			_changeHandlers.Add(onchanged);
 		}
 
+		internal bool CanRecycle => _canRecycle;
 		Element IElement.Parent
 		{
 			get { return _parent; }
diff --git a/Xamarin.Forms.Core/ITemplatedItemsList.cs b/Xamarin.Forms.Core/ITemplatedItemsList.cs
index be9055af..ded42597 100644
--- a/Xamarin.Forms.Core/ITemplatedItemsList.cs
+++ b/Xamarin.Forms.Core/ITemplatedItemsList.cs
@@ -19,6 +19,7 @@ namespace Xamarin.Forms
 
 		IListProxy ListProxy { get; }
 
+		DataTemplate SelectDataTemplate(object item);
 		int GetGlobalIndexForGroup(ITemplatedItemsList<TItem> group);
 		int GetGlobalIndexOfItem(object item);
 		ITemplatedItemsList<TItem> GetGroup(int index);
diff --git a/Xamarin.Forms.Core/ItemsView.cs b/Xamarin.Forms.Core/ItemsView.cs
index 33114f3c..4efa7221 100644
--- a/Xamarin.Forms.Core/ItemsView.cs
+++ b/Xamarin.Forms.Core/ItemsView.cs
@@ -86,13 +86,18 @@ namespace Xamarin.Forms
 			element.Parent = (Element)bindable;
 		}
 
-		static bool ValidateItemTemplate(BindableObject b, object v)
+		static bool ValidateItemTemplate(BindableObject bindable, object value)
 		{
-			var lv = b as ListView;
-			if (lv == null)
+			var listView = bindable as ListView;
+			if (listView == null)
 				return true;
 
-			return !(lv.CachingStrategy == ListViewCachingStrategy.RetainElement && lv.ItemTemplate is DataTemplateSelector);
+			var isRetainStrategy = listView.CachingStrategy == ListViewCachingStrategy.RetainElement;
+			var isDataTemplateSelector = listView.ItemTemplate is DataTemplateSelector;
+			if (isRetainStrategy && isDataTemplateSelector)
+				return false;
+
+			return true;
 		}
 	}
 }
\ No newline at end of file
diff --git a/Xamarin.Forms.Core/ListView.cs b/Xamarin.Forms.Core/ListView.cs
index 0a739416..ce6bc1cc 100644
--- a/Xamarin.Forms.Core/ListView.cs
+++ b/Xamarin.Forms.Core/ListView.cs
@@ -73,7 +73,11 @@ namespace Xamarin.Forms
 
 		public ListView([Parameter("CachingStrategy")] ListViewCachingStrategy cachingStrategy) : this()
 		{
-			if (Device.RuntimePlatform == Device.Android || Device.RuntimePlatform == Device.iOS || Device.RuntimePlatform == Device.macOS)
+			// null => UnitTest "platform"
+			if (Device.RuntimePlatform == null || 
+				Device.RuntimePlatform == Device.Android || 
+				Device.RuntimePlatform == Device.iOS || 
+				Device.RuntimePlatform == Device.macOS)
 				CachingStrategy = cachingStrategy;
 		}
 
diff --git a/Xamarin.Forms.Core/ListViewCachingStrategy.cs b/Xamarin.Forms.Core/ListViewCachingStrategy.cs
index 7dd90196..d45519a5 100644
--- a/Xamarin.Forms.Core/ListViewCachingStrategy.cs
+++ b/Xamarin.Forms.Core/ListViewCachingStrategy.cs
@@ -1,8 +1,12 @@
+using System;
+
 namespace Xamarin.Forms
 {
+	[Flags]
 	public enum ListViewCachingStrategy
 	{
 		RetainElement = 0,
-		RecycleElement
+		RecycleElement = 1 << 0,
+		RecycleElementAndDataTemplate = RecycleElement | 1 << 1,
 	}
 }
\ No newline at end of file
diff --git a/Xamarin.Forms.Core/TemplatedItemsList.cs b/Xamarin.Forms.Core/TemplatedItemsList.cs
index 31823c8e..417947c8 100644
--- a/Xamarin.Forms.Core/TemplatedItemsList.cs
+++ b/Xamarin.Forms.Core/TemplatedItemsList.cs
@@ -523,13 +523,19 @@ namespace Xamarin.Forms.Internals
 			return GetIndex(item);
 		}
 
+		[EditorBrowsable(EditorBrowsableState.Never)]
+		public DataTemplate SelectDataTemplate(object item)
+		{
+			return ItemTemplate.SelectDataTemplate(item, _itemsView);
+		}
+
 		public TItem CreateContent(int index, object item, bool insert = false)
 		{
 			TItem content = ItemTemplate != null ? (TItem)ItemTemplate.CreateContent(item, _itemsView) : _itemsView.CreateDefault(item);
 
 			content = UpdateContent(content, index, item);
 
-			if (CachingStrategy == ListViewCachingStrategy.RecycleElement)
+			if ((CachingStrategy & ListViewCachingStrategy.RecycleElement) != 0)
 				return content;
 
 			for (int i = _templatedObjects.Count; i <= index; i++)
@@ -891,7 +897,7 @@ namespace Xamarin.Forms.Internals
 
 		void OnGroupingEnabledChanged()
 		{
-			if (CachingStrategy == ListViewCachingStrategy.RecycleElement)
+			if ((CachingStrategy & ListViewCachingStrategy.RecycleElement) != 0)
 				_templatedObjects.Clear();
 
 			OnItemsSourceChanged(true);
@@ -963,7 +969,7 @@ namespace Xamarin.Forms.Internals
 				return;
 			}
 
-			if (CachingStrategy == ListViewCachingStrategy.RecycleElement)
+			if ((CachingStrategy & ListViewCachingStrategy.RecycleElement) != 0)
 			{
 				OnCollectionChanged(e);
 				return;
diff --git a/Xamarin.Forms.Platform.MacOS/Renderers/ListViewDataSource.cs b/Xamarin.Forms.Platform.MacOS/Renderers/ListViewDataSource.cs
index 1a9cf7f0..ecc67f6a 100644
--- a/Xamarin.Forms.Platform.MacOS/Renderers/ListViewDataSource.cs
+++ b/Xamarin.Forms.Platform.MacOS/Renderers/ListViewDataSource.cs
@@ -162,7 +162,7 @@ namespace Xamarin.Forms.Platform.MacOS
 				cell = GetCellForPath(indexPath, isHeader);
 				nativeCell = CellNSView.GetNativeCell(tableView, cell, templateId, isHeader);
 			}
-			else if (cachingStrategy == ListViewCachingStrategy.RecycleElement)
+			else if ((cachingStrategy & ListViewCachingStrategy.RecycleElement) != 0)
 			{
 				nativeCell = tableView.MakeView(templateId, tableView);
 				if (nativeCell == null)
diff --git a/Xamarin.Forms.Platform.iOS/ContextActionCell.cs b/Xamarin.Forms.Platform.iOS/ContextActionCell.cs
index 45f54340..1b0f5103 100644
--- a/Xamarin.Forms.Platform.iOS/ContextActionCell.cs
+++ b/Xamarin.Forms.Platform.iOS/ContextActionCell.cs
@@ -118,7 +118,8 @@ namespace Xamarin.Forms.Platform.iOS
 		public void Update(UITableView tableView, Cell cell, UITableViewCell nativeCell)
 		{
 			var parentListView = cell.RealParent as ListView;
-			var recycling = parentListView != null && parentListView.CachingStrategy == ListViewCachingStrategy.RecycleElement;
+			var recycling = parentListView != null && 
+				((parentListView.CachingStrategy & ListViewCachingStrategy.RecycleElement) != 0);
 			if (_cell != cell && recycling)
 			{
 				if (_cell != null)
@@ -459,7 +460,8 @@ namespace Xamarin.Forms.Platform.iOS
 			if (e.PropertyName == "HasContextActions")
 			{
 				var parentListView = _cell.RealParent as ListView;
-				var recycling = parentListView != null && parentListView.CachingStrategy == ListViewCachingStrategy.RecycleElement;
+				var recycling = parentListView != null && 
+					((parentListView.CachingStrategy & ListViewCachingStrategy.RecycleElement) != 0);
 				if (!recycling)
 					ReloadRow();
 			}
@@ -468,7 +470,8 @@ namespace Xamarin.Forms.Platform.iOS
 		void OnContextItemsChanged(object sender, NotifyCollectionChangedEventArgs e)
 		{
 			var parentListView = _cell.RealParent as ListView;
-			var recycling = parentListView != null && parentListView.CachingStrategy == ListViewCachingStrategy.RecycleElement;
+			var recycling = parentListView != null && 
+				((parentListView.CachingStrategy & ListViewCachingStrategy.RecycleElement) != 0);
 			if (recycling)
 				Update(_tableView, _cell, ContentCell);
 			else
@@ -479,7 +482,8 @@ namespace Xamarin.Forms.Platform.iOS
 		void OnMenuItemPropertyChanged(object sender, PropertyChangedEventArgs e)
 		{
 			var parentListView = _cell.RealParent as ListView;
-			var recycling = parentListView != null && parentListView.CachingStrategy == ListViewCachingStrategy.RecycleElement;
+			var recycling = parentListView != null && 
+				((parentListView.CachingStrategy & ListViewCachingStrategy.RecycleElement) != 0);
 			if (recycling)
 				Update(_tableView, _cell, ContentCell);
 			else
diff --git a/Xamarin.Forms.Platform.iOS/Renderers/ListViewRenderer.cs b/Xamarin.Forms.Platform.iOS/Renderers/ListViewRenderer.cs
index 7fd68cc0..f6cccd54 100644
--- a/Xamarin.Forms.Platform.iOS/Renderers/ListViewRenderer.cs
+++ b/Xamarin.Forms.Platform.iOS/Renderers/ListViewRenderer.cs
@@ -25,7 +25,6 @@ namespace Xamarin.Forms.Platform.iOS
 		KeyboardInsetTracker _insetTracker;
 		RectangleF _previousFrame;
 		ScrollToRequestedEventArgs _requestedScroll;
-		bool _shouldEstimateRowHeight = true;
 
 		FormsUITableViewController _tableViewController;
 		ListView ListView => Element;
@@ -212,7 +211,6 @@ namespace Xamarin.Forms.Platform.iOS
 						Control.SetContentOffset(offset, true);
 					});
 				}
-				_shouldEstimateRowHeight = true;
 
 				var listView = e.NewElement;
 
@@ -366,35 +364,36 @@ namespace Xamarin.Forms.Platform.iOS
 
 		void UpdateEstimatedRowHeight()
 		{
-			var rowHeight = Element.RowHeight;
-			if (Element.HasUnevenRows && rowHeight == -1)
-			{
-				var source = _dataSource as UnevenListViewDataSource;
-
-				// We want to make sure we reset the cached defined row heights whenever this is called.
-				// Failing to do this will regress Bugzilla 43313 (strange animation when adding rows with uneven heights)
-				source?.CacheDefinedRowHeights();
+			if (_estimatedRowHeight)
+				return;
 
-				if (_shouldEstimateRowHeight && !_estimatedRowHeight)
-				{
-					if (source != null)
-					{
-						Control.EstimatedRowHeight = source.GetEstimatedRowHeight(Control);
-						_estimatedRowHeight = true;
-					}
-					else
-					{
-						//We need to set a default estimated row height, because re-setting it later(when we have items on the TIL)
-						//will cause the UITableView to reload, and throw an Exception
-						Control.EstimatedRowHeight = DefaultRowHeight;
-					}
-				}
-			}
-			else if (!_estimatedRowHeight)
+			// if even rows OR uneven rows but user specified a row height anyway...
+			if (!Element.HasUnevenRows || Element.RowHeight != -1)
 			{
 				Control.EstimatedRowHeight = 0;
 				_estimatedRowHeight = true;
+				return;
 			}
+
+			var source = _dataSource as UnevenListViewDataSource;
+
+			// We want to make sure we reset the cached defined row heights whenever this is called.
+			// Failing to do this will regress Bugzilla 43313 
+			// (strange animation when adding rows with uneven heights)
+			//source?.CacheDefinedRowHeights();
+
+			if (source == null)
+			{
+				// We need to set a default estimated row height, 
+				// because re-setting it later(when we have items on the TIL)
+				// will cause the UITableView to reload, and throw an Exception
+				Control.EstimatedRowHeight = DefaultRowHeight;
+				return;
+			}
+
+			Control.EstimatedRowHeight = source.GetEstimatedRowHeight(Control);
+			_estimatedRowHeight = true;
+			return;
 		}
 
 		void UpdateFooter()
@@ -627,9 +626,7 @@ namespace Xamarin.Forms.Platform.iOS
 		{
 			IVisualElementRenderer _prototype;
 			bool _disposed;
-			bool _useEstimatedRowHeight;
-
-			ConcurrentDictionary<NSIndexPath, nfloat> _rowHeights = new ConcurrentDictionary<NSIndexPath, nfloat>();
+			Dictionary<object, Cell> _prototypicalCellByTypeOrDataTemplate = new Dictionary<object, Cell>();
 
 			public UnevenListViewDataSource(ListView list, FormsUITableViewController uiTableViewController) : base(list, uiTableViewController)
 			{
@@ -639,24 +636,6 @@ namespace Xamarin.Forms.Platform.iOS
 			{
 			}
 
-			internal void CacheDefinedRowHeights()
-			{
-				Task.Run(() =>
-				{
-					var templatedItems = TemplatedItemsView.TemplatedItems;
-
-					foreach (var cell in templatedItems)
-					{
-						if (_disposed)
-							return;
-
-						double? cellRenderHeight = cell?.RenderHeight;
-						if (cellRenderHeight > 0)
-							_rowHeights[cell.GetIndexPath()] = (nfloat)cellRenderHeight;
-					}
-				});
-			}
-
 			internal nfloat GetEstimatedRowHeight(UITableView table)
 			{
 				if (List.RowHeight != -1)
@@ -692,22 +671,42 @@ namespace Xamarin.Forms.Platform.iOS
 				return CalculateHeightForCell(table, firstCell);
 			}
 
-			public override nfloat EstimatedHeight(UITableView tableView, NSIndexPath indexPath)
+			internal override void InvalidatePrototypicalCellCache()
+			{
+				_prototypicalCellByTypeOrDataTemplate.Clear();
+			}
+
+			internal Cell GetPrototypicalCell(NSIndexPath indexPath)
 			{
-				if (_useEstimatedRowHeight)
-					return tableView.EstimatedRowHeight;
+				var itemTypeOrDataTemplate = default(object);
+
+				var cachingStrategy = List.CachingStrategy;
+				if (cachingStrategy == ListViewCachingStrategy.RecycleElement)
+					itemTypeOrDataTemplate = GetDataTemplateForPath(indexPath);
+
+				else if (cachingStrategy == ListViewCachingStrategy.RecycleElementAndDataTemplate)
+					itemTypeOrDataTemplate = GetItemTypeForPath(indexPath);
+
+				else // ListViewCachingStrategy.RetainElement
+					return GetCellForPath(indexPath);
 
-				// Note: It is *not* an optimization to first check if the array has any values.
-				nfloat specifiedRowHeight;
-				if (_rowHeights.TryGetValue(indexPath, out specifiedRowHeight) && specifiedRowHeight > 0)
-					return specifiedRowHeight;
 
-				return UITableView.AutomaticDimension;
+				Cell protoCell;
+				if (!_prototypicalCellByTypeOrDataTemplate.TryGetValue(itemTypeOrDataTemplate, out protoCell))
+				{
+					// cache prototypical cell by item type; Items of the same Type share
+					// the same DataTemplate (this is enforced by RecycleElementAndDataTemplate)
+					protoCell = GetCellForPath(indexPath);
+					_prototypicalCellByTypeOrDataTemplate[itemTypeOrDataTemplate] = protoCell;
+				}
+
+				var templatedItems = GetTemplatedItemsListForPath(indexPath);
+				return templatedItems.UpdateContent(protoCell, indexPath.Row);
 			}
 
 			public override nfloat GetHeightForRow(UITableView tableView, NSIndexPath indexPath)
 			{
-				var cell = GetCellForPath(indexPath);
+				var cell = GetPrototypicalCell(indexPath);
 
 				if (List.RowHeight == -1 && cell.Height == -1 && cell is ViewCell)
 					return UITableView.AutomaticDimension;
@@ -745,7 +744,7 @@ namespace Xamarin.Forms.Platform.iOS
 
 					// Let the EstimatedHeight method know to use this value.
 					// Much more efficient than checking the value each time.
-					_useEstimatedRowHeight = true;
+					//_useEstimatedRowHeight = true;
 					return (nfloat)req.Request.Height;
 				}
 
@@ -818,6 +817,10 @@ namespace Xamarin.Forms.Platform.iOS
 				get { return UIColor.Clear; }
 			}
 
+			internal virtual void InvalidatePrototypicalCellCache()
+			{
+			}
+
 			public override void DraggingEnded(UIScrollView scrollView, bool willDecelerate)
 			{
 				_isDragging = false;
@@ -840,13 +843,14 @@ namespace Xamarin.Forms.Platform.iOS
 					cell = GetCellForPath(indexPath);
 					nativeCell = CellTableViewCell.GetNativeCell(tableView, cell);
 				}
-				else if (cachingStrategy == ListViewCachingStrategy.RecycleElement)
+				else if ((cachingStrategy & ListViewCachingStrategy.RecycleElement) != 0)
 				{
 					var id = TemplateIdForPath(indexPath);
 					nativeCell = tableView.DequeueReusableCell(ContextActionsCell.Key + id);
 					if (nativeCell == null)
 					{
 						cell = GetCellForPath(indexPath);
+
 						nativeCell = CellTableViewCell.GetNativeCell(tableView, cell, true, id.ToString());
 					}
 					else
@@ -966,7 +970,7 @@ namespace Xamarin.Forms.Platform.iOS
 					return;
 
 				Cell formsCell = null;
-				if (List.CachingStrategy == ListViewCachingStrategy.RecycleElement)
+				if ((List.CachingStrategy & ListViewCachingStrategy.RecycleElement) != 0)
 					formsCell = (Cell)((INativeElementView)cell).Element;
 
 				SetCellBackgroundColor(cell, UIColor.Clear);
@@ -1035,12 +1039,32 @@ namespace Xamarin.Forms.Platform.iOS
 				_uiTableView.ReloadData();
 			}
 
-			protected Cell GetCellForPath(NSIndexPath indexPath)
+			protected ITemplatedItemsList<Cell> GetTemplatedItemsListForPath(NSIndexPath indexPath)
 			{
 				var templatedItems = TemplatedItemsView.TemplatedItems;
 				if (List.IsGroupingEnabled)
-					templatedItems = (TemplatedItemsList<ItemsView<Cell>, Cell>)((IList)templatedItems)[indexPath.Section];
+					templatedItems = (ITemplatedItemsList<Cell>)((IList)templatedItems)[indexPath.Section];
 
+				return templatedItems;
+			}
+
+			protected DataTemplate GetDataTemplateForPath(NSIndexPath indexPath)
+			{
+				var templatedList = GetTemplatedItemsListForPath(indexPath);
+				var item = templatedList.ListProxy[indexPath.Row];
+				return templatedList.SelectDataTemplate(item);
+			}
+
+			protected Type GetItemTypeForPath(NSIndexPath indexPath)
+			{
+				var templatedList = GetTemplatedItemsListForPath(indexPath);
+				var item = templatedList.ListProxy[indexPath.Row];
+				return item.GetType();
+			}
+
+			protected Cell GetCellForPath(NSIndexPath indexPath)
+			{
+				var templatedItems = GetTemplatedItemsListForPath(indexPath);
 				var cell = templatedItems[indexPath.Row];
 				return cell;
 			}
@@ -1086,10 +1110,7 @@ namespace Xamarin.Forms.Platform.iOS
 				if (selector == null)
 					return DefaultItemTemplateId;
 
-				var templatedList = TemplatedItemsView.TemplatedItems;
-				if (List.IsGroupingEnabled)
-					templatedList = (TemplatedItemsList<ItemsView<Cell>, Cell>)((IList)templatedList)[indexPath.Section];
-
+				var templatedList = GetTemplatedItemsListForPath(indexPath);
 				var item = templatedList.ListProxy[indexPath.Row];
 
 				itemTemplate = selector.SelectTemplate(item, List);
diff --git a/docs/Xamarin.Forms.Core/Xamarin.Forms.Internals/DataTemplateExtensions.xml b/docs/Xamarin.Forms.Core/Xamarin.Forms.Internals/DataTemplateExtensions.xml
index 9483388d..90f2f672 100644
--- a/docs/Xamarin.Forms.Core/Xamarin.Forms.Internals/DataTemplateExtensions.xml
+++ b/docs/Xamarin.Forms.Core/Xamarin.Forms.Internals/DataTemplateExtensions.xml
@@ -43,5 +43,29 @@
         <remarks>To be added.</remarks>
       </Docs>
     </Member>
+    <Member MemberName="SelectDataTemplate">
+      <MemberSignature Language="C#" Value="public static Xamarin.Forms.DataTemplate SelectDataTemplate (this Xamarin.Forms.DataTemplate self, object item, Xamarin.Forms.BindableObject container);" />
+      <MemberSignature Language="ILAsm" Value=".method public static hidebysig class Xamarin.Forms.DataTemplate SelectDataTemplate(class Xamarin.Forms.DataTemplate self, object item, class Xamarin.Forms.BindableObject container) cil managed" />
+      <MemberType>Method</MemberType>
+      <AssemblyInfo>
+        <AssemblyVersion>2.0.0.0</AssemblyVersion>
+      </AssemblyInfo>
+      <ReturnValue>
+        <ReturnType>Xamarin.Forms.DataTemplate</ReturnType>
+      </ReturnValue>
+      <Parameters>
+        <Parameter Name="self" Type="Xamarin.Forms.DataTemplate" RefType="this" />
+        <Parameter Name="item" Type="System.Object" />
+        <Parameter Name="container" Type="Xamarin.Forms.BindableObject" />
+      </Parameters>
+      <Docs>
+        <param name="self">To be added.</param>
+        <param name="item">To be added.</param>
+        <param name="container">To be added.</param>
+        <summary>To be added.</summary>
+        <returns>To be added.</returns>
+        <remarks>To be added.</remarks>
+      </Docs>
+    </Member>
   </Members>
 </Type>
diff --git a/docs/Xamarin.Forms.Core/Xamarin.Forms.Internals/TemplatedItemsList`2.xml b/docs/Xamarin.Forms.Core/Xamarin.Forms.Internals/TemplatedItemsList`2.xml
index cca38797..6d000dd8 100644
--- a/docs/Xamarin.Forms.Core/Xamarin.Forms.Internals/TemplatedItemsList`2.xml
+++ b/docs/Xamarin.Forms.Core/Xamarin.Forms.Internals/TemplatedItemsList`2.xml
@@ -558,6 +558,31 @@
         <remarks>To be added.</remarks>
       </Docs>
     </Member>
+    <Member MemberName="SelectDataTemplate">
+      <MemberSignature Language="C#" Value="public Xamarin.Forms.DataTemplate SelectDataTemplate (object item);" />
+      <MemberSignature Language="ILAsm" Value=".method public hidebysig newslot virtual instance class Xamarin.Forms.DataTemplate SelectDataTemplate(object item) cil managed" />
+      <MemberType>Method</MemberType>
+      <AssemblyInfo>
+        <AssemblyVersion>2.0.0.0</AssemblyVersion>
+      </AssemblyInfo>
+      <Attributes>
+        <Attribute>
+          <AttributeName>System.ComponentModel.EditorBrowsable(System.ComponentModel.EditorBrowsableState.Never)</AttributeName>
+        </Attribute>
+      </Attributes>
+      <ReturnValue>
+        <ReturnType>Xamarin.Forms.DataTemplate</ReturnType>
+      </ReturnValue>
+      <Parameters>
+        <Parameter Name="item" Type="System.Object" />
+      </Parameters>
+      <Docs>
+        <param name="item">To be added.</param>
+        <summary>To be added.</summary>
+        <returns>To be added.</returns>
+        <remarks>To be added.</remarks>
+      </Docs>
+    </Member>
     <Member MemberName="ShortName">
       <MemberSignature Language="C#" Value="public string ShortName { get; set; }" />
       <MemberSignature Language="ILAsm" Value=".property instance string ShortName" />
diff --git a/docs/Xamarin.Forms.Core/Xamarin.Forms/ITemplatedItemsList`1.xml b/docs/Xamarin.Forms.Core/Xamarin.Forms/ITemplatedItemsList`1.xml
index a2418ea4..94bcbe67 100644
--- a/docs/Xamarin.Forms.Core/Xamarin.Forms/ITemplatedItemsList`1.xml
+++ b/docs/Xamarin.Forms.Core/Xamarin.Forms/ITemplatedItemsList`1.xml
@@ -286,6 +286,26 @@
         <remarks>To be added.</remarks>
       </Docs>
     </Member>
+    <Member MemberName="SelectDataTemplate">
+      <MemberSignature Language="C#" Value="public Xamarin.Forms.DataTemplate SelectDataTemplate (object item);" />
+      <MemberSignature Language="ILAsm" Value=".method public hidebysig newslot virtual instance class Xamarin.Forms.DataTemplate SelectDataTemplate(object item) cil managed" />
+      <MemberType>Method</MemberType>
+      <AssemblyInfo>
+        <AssemblyVersion>2.0.0.0</AssemblyVersion>
+      </AssemblyInfo>
+      <ReturnValue>
+        <ReturnType>Xamarin.Forms.DataTemplate</ReturnType>
+      </ReturnValue>
+      <Parameters>
+        <Parameter Name="item" Type="System.Object" />
+      </Parameters>
+      <Docs>
+        <param name="item">To be added.</param>
+        <summary>To be added.</summary>
+        <returns>To be added.</returns>
+        <remarks>To be added.</remarks>
+      </Docs>
+    </Member>
     <Member MemberName="ShortNames">
       <MemberSignature Language="C#" Value="public System.Collections.Generic.IReadOnlyList&lt;string&gt; ShortNames { get; }" />
       <MemberSignature Language="ILAsm" Value=".property instance class System.Collections.Generic.IReadOnlyList`1&lt;string&gt; ShortNames" />
diff --git a/docs/Xamarin.Forms.Core/Xamarin.Forms/ListViewCachingStrategy.xml b/docs/Xamarin.Forms.Core/Xamarin.Forms/ListViewCachingStrategy.xml
index 4aca0cf0..4eb2ba3a 100644
--- a/docs/Xamarin.Forms.Core/Xamarin.Forms/ListViewCachingStrategy.xml
+++ b/docs/Xamarin.Forms.Core/Xamarin.Forms/ListViewCachingStrategy.xml
@@ -9,6 +9,11 @@
   <Base>
     <BaseTypeName>System.Enum</BaseTypeName>
   </Base>
+  <Attributes>
+    <Attribute>
+      <AttributeName>System.Flags</AttributeName>
+    </Attribute>
+  </Attributes>
   <Docs>
     <summary>Enumerates caching strategies for a ListView.</summary>
     <remarks>
@@ -48,6 +53,20 @@
         <summary>Indicates that unneeded cells will have their binding contexts updated to that of a cell that is needed.</summary>
       </Docs>
     </Member>
+    <Member MemberName="RecycleElementAndDataTemplate">
+      <MemberSignature Language="C#" Value="RecycleElementAndDataTemplate" />
+      <MemberSignature Language="ILAsm" Value=".field public static literal valuetype Xamarin.Forms.ListViewCachingStrategy RecycleElementAndDataTemplate = int32(3)" />
+      <MemberType>Field</MemberType>
+      <AssemblyInfo>
+        <AssemblyVersion>2.0.0.0</AssemblyVersion>
+      </AssemblyInfo>
+      <ReturnValue>
+        <ReturnType>Xamarin.Forms.ListViewCachingStrategy</ReturnType>
+      </ReturnValue>
+      <Docs>
+        <summary>To be added.</summary>
+      </Docs>
+    </Member>
     <Member MemberName="RetainElement">
       <MemberSignature Language="C#" Value="RetainElement" />
       <MemberSignature Language="ILAsm" Value=".field public static literal valuetype Xamarin.Forms.ListViewCachingStrategy RetainElement = int32(0)" />
diff --git a/docs/Xamarin.Forms.Core/index.xml b/docs/Xamarin.Forms.Core/index.xml
index 16c1cfa1..1b13e335 100644
--- a/docs/Xamarin.Forms.Core/index.xml
+++ b/docs/Xamarin.Forms.Core/index.xml
@@ -1072,6 +1072,31 @@
     </ExtensionMethod>
     <ExtensionMethod>
       <Targets>
+        <Target Type="T:Xamarin.Forms.DataTemplate" />
+      </Targets>
+      <Member MemberName="SelectDataTemplate">
+        <MemberSignature Language="C#" Value="public static Xamarin.Forms.DataTemplate SelectDataTemplate (this Xamarin.Forms.DataTemplate self, object item, Xamarin.Forms.BindableObject container);" />
+        <MemberSignature Language="ILAsm" Value=".method public static hidebysig class Xamarin.Forms.DataTemplate SelectDataTemplate(class Xamarin.Forms.DataTemplate self, object item, class Xamarin.Forms.BindableObject container) cil managed" />
+        <MemberType>ExtensionMethod</MemberType>
+        <ReturnValue>
+          <ReturnType>Xamarin.Forms.DataTemplate</ReturnType>
+        </ReturnValue>
+        <Parameters>
+          <Parameter Name="self" Type="Xamarin.Forms.DataTemplate" RefType="this" />
+          <Parameter Name="item" Type="System.Object" />
+          <Parameter Name="container" Type="Xamarin.Forms.BindableObject" />
+        </Parameters>
+        <Docs>
+          <param name="self">To be added.</param>
+          <param name="item">To be added.</param>
+          <param name="container">To be added.</param>
+          <summary>To be added.</summary>
+        </Docs>
+        <Link Type="Xamarin.Forms.Internals.DataTemplateExtensions" Member="M:Xamarin.Forms.Internals.DataTemplateExtensions.SelectDataTemplate(Xamarin.Forms.DataTemplate,System.Object,Xamarin.Forms.BindableObject)" />
+      </Member>
+    </ExtensionMethod>
+    <ExtensionMethod>
+      <Targets>
         <Target Type="T:Xamarin.Forms.Internals.DeviceOrientation" />
       </Targets>
       <Member MemberName="IsLandscape">