Allocate prototypical view for RetainElement (#1226)

Author: kingces95

Xamarin.Forms.Core/TemplatedItemsList.cs

@@ -529,12 +529,19 @@ public DataTemplate SelectDataTemplate(object item)
 			return ItemTemplate.SelectDataTemplate(item, _itemsView);
 		}
 
-		public TItem CreateContent(int index, object item, bool insert = false)
+		public TItem ActivateContent(int index, object item)
 		{
 			TItem content = ItemTemplate != null ? (TItem)ItemTemplate.CreateContent(item, _itemsView) : _itemsView.CreateDefault(item);
 
 			content = UpdateContent(content, index, item);
 
+			return content;
+		}
+
+		public TItem CreateContent(int index, object item, bool insert = false)
+		{
+			var content = ActivateContent(index, item);
+
 			if ((CachingStrategy & ListViewCachingStrategy.RecycleElement) != 0)
 				return content;
 

Xamarin.Forms.Platform.iOS/Renderers/ListViewRenderer.cs

@@ -678,16 +678,7 @@ internal nfloat GetEstimatedRowHeight(UITableView table)
 				}
 
 				// We're going to base our estimate off of the first cell
-				var isGroupingEnabled = List.IsGroupingEnabled;
-
-				if (isGroupingEnabled)
-					templatedItems = templatedItems.GetGroup(0);
-
-				object item = null;
-				if (templatedItems == null || templatedItems.ListProxy.TryGetValue(0, out item) == false)
-					return DefaultRowHeight;
-
-				var firstCell = templatedItems.ActivateContent(0, item);
+				var firstCell = templatedItems.ActivateContent(0, templatedItems.ListProxy[0]);
 
 				// Let's skip this optimization for grouped lists. It will likely cause more trouble than it's worth.
 				if (firstCell?.Height > 0 && !isGroupingEnabled)
@@ -778,7 +769,8 @@ internal nfloat CalculateHeightForCell(UITableView tableView, Cell cell)
 					// Let the EstimatedHeight method know to use this value.
 					// Much more efficient than checking the value each time.
 					//_useEstimatedRowHeight = true;
-					return (nfloat)req.Request.Height;
+					var height = (nfloat)req.Request.Height;
+					return height > 1 ? height : DefaultRowHeight;
 				}
 
 				var renderHeight = cell.RenderHeight;