[iOS] ActivityIndicator should not disappear when used in a ViewCell (#495)

* preserve activity indicator state

* changed to using listviewrenderer

* remove whitespace

* moved message to constructor

* add sample code

* remove message sending

* changes

* remove curly braces

Xamarin.Forms.Controls.Issues/Xamarin.Forms.Controls.Issues.Shared/Bugzilla44980.cs

@@ -0,0 +1,44 @@
+using System.Collections.Generic;
+using Xamarin.Forms.CustomAttributes;
+using Xamarin.Forms.Internals;
+
+#if UITEST
+using Xamarin.UITest;
+using NUnit.Framework;
+#endif
+
+namespace Xamarin.Forms.Controls
+{
+	[Preserve(AllMembers = true)]
+	[Issue(IssueTracker.Bugzilla, 44980, "ActivityIndicator disappears when scrolling", PlatformAffected.iOS)]
+	public class Bugzilla44980 : TestContentPage
+	{
+		protected override void Init()
+		{
+			var list = new List<string>();
+			for (var i = 0; i < 100; i++)
+				list.Add(i.ToString());
+
+			Content = new CListView
+			{
+				ItemsSource = list,
+				ItemTemplate = new DataTemplate(() =>
+				{
+					var activityIndicator = new ActivityIndicator
+					{
+						IsRunning = true,
+						IsVisible = true
+					};
+					return new ViewCell { View = activityIndicator };
+				})
+			};
+		}
+	}
+
+	public class CListView : ListView
+	{
+		public CListView() : base(ListViewCachingStrategy.RecycleElement)
+		{
+		}
+	}
+}

Xamarin.Forms.Controls.Issues/Xamarin.Forms.Controls.Issues.Shared/Xamarin.Forms.Controls.Issues.Shared.projitems

@@ -169,6 +169,7 @@
     <Compile Include="$(MSBuildThisFileDirectory)Bugzilla42832.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Bugzilla44044.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Bugzilla44338.cs" />
+    <Compile Include="$(MSBuildThisFileDirectory)Bugzilla44980.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Bugzilla45067.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Bugzilla45027.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Bugzilla45330.cs" />

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

@@ -44,5 +44,11 @@ namespace Xamarin.Forms.Platform.iOS
 			else
 				Control.StopAnimating();
 		}
+
+		internal void PreserveState()
+		{
+			if (Control != null && !Control.IsAnimating && Element != null && Element.IsRunning)
+				Control.StartAnimating();
+		}
 	}
 }

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

@@ -780,12 +780,13 @@ namespace Xamarin.Forms.Platform.iOS
 
 			public override UITableViewCell GetCell(UITableView tableView, NSIndexPath indexPath)
 			{
-				UITableViewCell nativeCell = null;
+				Cell cell;
+				UITableViewCell nativeCell;
 
 				var cachingStrategy = Controller.CachingStrategy;
 				if (cachingStrategy == ListViewCachingStrategy.RetainElement)
 				{
-					var cell = GetCellForPath(indexPath);
+					cell = GetCellForPath(indexPath);
 					nativeCell = CellTableViewCell.GetNativeCell(tableView, cell);
 				}
 				else if (cachingStrategy == ListViewCachingStrategy.RecycleElement)
@@ -794,13 +795,13 @@ namespace Xamarin.Forms.Platform.iOS
 					nativeCell = tableView.DequeueReusableCell(ContextActionsCell.Key + id);
 					if (nativeCell == null)
 					{
-						var cell = GetCellForPath(indexPath);
+						cell = GetCellForPath(indexPath);
 						nativeCell = CellTableViewCell.GetNativeCell(tableView, cell, true, id.ToString());
 					}
 					else
 					{
 						var templatedList = TemplatedItemsView.TemplatedItems.GetGroup(indexPath.Section);
-						var cell = (Cell)((INativeElementView)nativeCell).Element;
+						cell = (Cell)((INativeElementView)nativeCell).Element;
 						ICellController controller = cell;
 						controller.SendDisappearing();
 						templatedList.UpdateContent(cell, indexPath.Row);
@@ -813,10 +814,10 @@ namespace Xamarin.Forms.Platform.iOS
 				var bgColor = tableView.IndexPathForSelectedRow != null && tableView.IndexPathForSelectedRow.Equals(indexPath) ? UIColor.Clear : DefaultBackgroundColor;
 
 				SetCellBackgroundColor(nativeCell, bgColor);
-
+				PreserveActivityIndicatorState(cell);
 				return nativeCell;
 			}
-
+		
 			public override nfloat GetHeightForHeader(UITableView tableView, nint section)
 			{
 				if (List.IsGroupingEnabled)
@@ -1079,6 +1080,24 @@ namespace Xamarin.Forms.Platform.iOS
 
 				base.Dispose(disposing);
 			}
+
+			void PreserveActivityIndicatorState(Element element)
+			{
+				if (element == null)
+					return;
+
+				var activityIndicator = element as ActivityIndicator;
+				if (activityIndicator != null)
+				{
+					var renderer = Platform.GetRenderer(activityIndicator) as ActivityIndicatorRenderer;
+					renderer?.PreserveState();
+				}
+				else
+				{
+					foreach (Element childElement in (element as IElementController).LogicalChildren)
+						PreserveActivityIndicatorState(childElement);
+				}
+			}
 		}
 	}