[iOS] Better fix for EstimatedRowHeight (#4365) fixes #4356

* [Controls] Add repo for issue #4356 * [iOS] Call UpdateEstimatedRowHeight on MainThread so it delays and reloads after the row is inserted * [IOS] Try remove UpdateEstimatedRowHeight * [iOS] Fix EstimatedRowHeight * [iOS] Consolidate EstimatedRowHeight calculation on the ListviewDataSource * [iOS] Fix InvalidateCache and clear estimatedRowHeight * [iOS] Use bool for checking if is empty Co-Authored-By: rmarinho <me@ruimarinho.net> * Update Xamarin.Forms.Platform.iOS/Renderers/ListViewRenderer.cs Co-Authored-By: rmarinho <me@ruimarinho.net> * Update Xamarin.Forms.Platform.iOS/Renderers/ListViewRenderer.cs Co-Authored-By: rmarinho <me@ruimarinho.net> * Update Xamarin.Forms.Platform.iOS/Renderers/ListViewRenderer.cs Co-Authored-By: rmarinho <me@ruimarinho.net> * [iOS] Fix rebase * [Build] Update submodule * [Build] Remove xcode select * [iOS] Don't disable EstimatedRowHeight on iOS10
2019-03-24 19:48:16 +00:00 · 2019-03-24 19:48:16 +00:00 · b0724320b4
--- a/Xamarin.Forms.Build
+++ b/Xamarin.Forms.Build
@ -1 +1 @@
-Subproject commit c5be7a66d068c26e8334202deda3a5fafc03a4b1
+Subproject commit bde6c61641ace9b90c39ffc12e97e9e590ce0f31
--- a/Xamarin.Forms.Controls.Issues/Xamarin.Forms.Controls.Issues.Shared/Issue4356.cs
+++ b/Xamarin.Forms.Controls.Issues/Xamarin.Forms.Controls.Issues.Shared/Issue4356.cs
@ -0,0 +1,190 @@
+using System;
+using System.Collections.Generic;
+
+using Xamarin.Forms;
+using System.Threading.Tasks;
+using System.Collections.ObjectModel;
+using System.ComponentModel;
+using Xamarin.Forms.CustomAttributes;
+using Xamarin.Forms.Internals;
+
+#if UITEST
+using Xamarin.UITest;
+using NUnit.Framework;
+#endif
+
+namespace Xamarin.Forms.Controls.Issues
+{
+	[Preserve(AllMembers = true)]
+	[Issue(IssueTracker.Github, 4356, "[iOS] NSInternalInconsistencyException thrown when adding item to ListView after clearing bound ObservableCollection")]
+	public partial class Issue4356 : TestContentPage
+	{
+#if UITEST
+		[Test]
+		public void Issue4356Test()
+		{
+			RunningApp.WaitForElement(q => q.Marked("Will this repo work?"));
+			RunningApp.WaitForElement(q => q.Marked("Remove item"));
+			RunningApp.Tap(q => q.Marked("Remove item"));
+			RunningApp.Tap(q => q.Marked("Remove item"));
+			RunningApp.Tap(q => q.Marked("Add item"));
+			RunningApp.WaitForElement(q => q.Marked("Added from Button Command"));
+		}
+#endif
+
+		FavoritesViewModel ViewModel
+		{
+			get { return BindingContext as FavoritesViewModel; }
+		}
+
+		public Issue4356()
+		{
+#if APP
+			InitializeComponent();
+			BindingContext = new FavoritesViewModel();
+
+			listView.SeparatorVisibility = SeparatorVisibility.Default;
+			listView.SeparatorColor = Color.FromHex("#ababab");
+
+			listView.ItemTapped += (sender, args) =>
+			{
+				if (listView.SelectedItem == null)
+					return;
+
+				//do nothing anyway
+				return;
+			};
+#endif
+
+		}
+
+		protected override void Init()
+		{
+
+		}
+
+#pragma warning disable 1998 // considered for removal
+		public async void OnDelete(object sender, EventArgs e)
+#pragma warning restore 1998
+		{
+			var mi = ((MenuItem)sender);
+			if (mi.CommandParameter == null)
+				return;
+
+			var articlelistingitem = mi.CommandParameter;
+
+			if (articlelistingitem != null)
+				DisplayAlert("Alert", "I'm not deleting just refreshing...", "Ok");
+			ViewModel.LoadFavoritesCommand.Execute(null);
+		}
+
+
+		protected override void OnAppearing()
+		{
+			base.OnAppearing();
+			if (ViewModel == null || !ViewModel.CanLoadMore || ViewModel.IsBusy)
+				return;
+
+			Device.BeginInvokeOnMainThread(() =>
+			{
+				ViewModel.LoadFavoritesCommand.Execute(null);
+			});
+		}
+
+		[Preserve(AllMembers = true)]
+		public class FavoritesViewModel : BaseViewModelF
+		{
+			public ObservableCollection<ArticleListing> FavoriteArticles { get; set; }
+			public int Count { get; private set; } = 0;
+			readonly object _listLock = new object();
+
+			public FavoritesViewModel()
+			{
+				Title = "Favorites";
+				FavoriteArticles = new ObservableCollection<ArticleListing>();
+				AddCommand = new Command(() =>
+				{
+					lock (_listLock)
+					{
+						FavoriteArticles.Add(new ArticleListing
+						{
+							ArticleTitle = "Added from Button Command",
+							AuthorString = "Rui Marinho",
+							FormattedPostedDate = "08-11-2018"
+						});
+					}
+				});
+
+				RemoveCommand = new Command(() =>
+				{
+					lock (_listLock)
+					{
+						if (FavoriteArticles.Count > 0)
+						{
+							FavoriteArticles.RemoveAt(FavoriteArticles.Count - 1);
+							--Count;
+						}
+					}
+				});
+
+			}
+
+			public Command AddCommand { get; }
+			public Command RemoveCommand { get; }
+
+
+			Command _loadFavoritesCommand;
+
+			public Command LoadFavoritesCommand
+			{
+				get
+				{
+					return _loadFavoritesCommand ??
+					(_loadFavoritesCommand = new Command(async () =>
+					{
+						await ExecuteFavoritesCommand();
+					}, () =>
+					{
+						return !IsBusy;
+					}));
+				}
+			}
+
+#pragma warning disable 1998 // considered for removal
+			public async Task ExecuteFavoritesCommand()
+#pragma warning restore 1998
+			{
+				if (IsBusy)
+					return;
+
+				IsBusy = true;
+				LoadFavoritesCommand.ChangeCanExecute();
+				FavoriteArticles.Clear();
+				var articles = new ObservableCollection<ArticleListing> {
+					new ArticleListing {
+						ArticleTitle = "Will this repo work?",
+						AuthorString = "Ben Crispin",
+						FormattedPostedDate = "7-28-2015"
+					},
+					new ArticleListing {
+						ArticleTitle = "Xamarin Forms BugZilla",
+						AuthorString = "Some Guy",
+						FormattedPostedDate = "7-28-2015"
+					}
+				};
+				var templist = new ObservableCollection<ArticleListing>();
+				foreach (var article in articles)
+				{
+					//templist.Add(article);
+					FavoriteArticles.Add(article);
+				}
+				//FavoriteArticles = templist;
+				OnPropertyChanged("FavoriteArticles");
+				IsBusy = false;
+				LoadFavoritesCommand.ChangeCanExecute();
+			}
+
+		}
+	}
+}
+
--- a/Xamarin.Forms.Controls.Issues/Xamarin.Forms.Controls.Issues.Shared/Issue4356.xaml
+++ b/Xamarin.Forms.Controls.Issues/Xamarin.Forms.Controls.Issues.Shared/Issue4356.xaml
@ -0,0 +1,42 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<local:TestContentPage xmlns="http://xamarin.com/schemas/2014/forms" xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml" xmlns:local="clr-namespace:Xamarin.Forms.Controls" x:Class="Xamarin.Forms.Controls.Issues.Issue4356">
+    <StackLayout Orientation="Vertical">
+        <StackLayout Orientation="Horizontal">
+            <Button Text="Add item" HorizontalOptions="CenterAndExpand" Command="{Binding AddCommand}" />
+            <Button Text="Remove item" HorizontalOptions="CenterAndExpand" Command="{Binding RemoveCommand}" />
+        </StackLayout>
+        <ListView x:Name="listView" 
+                  ItemsSource="{Binding FavoriteArticles}" 
+                  HasUnevenRows="True" 
+                  IsPullToRefreshEnabled="True" 
+                  HorizontalOptions="FillAndExpand"
+                  VerticalOptions="FillAndExpand"
+                  SeparatorVisibility="None"
+                  SeparatorColor="Transparent"
+                  BackgroundColor="#F0F0F0"
+                  RefreshCommand="{Binding LoadFavoritesCommand}" 
+                  IsRefreshing="{Binding IsBusy, Mode=OneWay}">
+            <ListView.ItemTemplate>
+                <DataTemplate>
+                    <ViewCell Height="85">
+                      <!--  <ViewCell.ContextActions>
+                            <MenuItem Clicked="OnDelete" CommandParameter="{Binding .}" Text="Delete" IsDestructive="True" />
+                        </ViewCell.ContextActions>-->
+                        <Grid Padding="10,5">
+                            <Grid.ColumnDefinitions>
+                                <ColumnDefinition Width="Auto" />
+                                <ColumnDefinition Width="*" />
+                            </Grid.ColumnDefinitions>
+                            <StackLayout Grid.Column="1" Padding="5" Spacing="1" VerticalOptions="Center">
+                                <Label Text="{Binding ArticleTitle}" FontSize="Medium" FontAttributes="Bold" TextColor="#333333" LineBreakMode="WordWrap" />
+                                <Label Text="{Binding AuthorString}" FontSize="Small" TextColor="#919191" LineBreakMode="TailTruncation" />
+                                <Label Text="{Binding FormattedPostedDate}" FontSize="Small" TextColor="#919191" LineBreakMode="NoWrap" />
+                                <Label Text="{Binding ItemId}" FontSize="Small" TextColor="#919191" LineBreakMode="NoWrap" IsVisible="false" />
+                            </StackLayout>
+                        </Grid>
+                    </ViewCell>
+                </DataTemplate>
+            </ListView.ItemTemplate>
+        </ListView>
+    </StackLayout>
+</local:TestContentPage>
--- a/Xamarin.Forms.Controls.Issues/Xamarin.Forms.Controls.Issues.Shared/Xamarin.Forms.Controls.Issues.Shared.projitems
+++ b/Xamarin.Forms.Controls.Issues/Xamarin.Forms.Controls.Issues.Shared/Xamarin.Forms.Controls.Issues.Shared.projitems
@ -887,6 +887,9 @@
    <Compile Include="$(MSBuildThisFileDirectory)Issue4314.cs" />
    <Compile Include="$(MSBuildThisFileDirectory)Issue5172.cs" />
    <Compile Include="$(MSBuildThisFileDirectory)Issue2204.cs" />
+    <Compile Include="$(MSBuildThisFileDirectory)Issue4356.cs">
+      <DependentUpon>Issue4356.xaml</DependentUpon>
+    </Compile>
  </ItemGroup>
  <ItemGroup>
    <EmbeddedResource Include="$(MSBuildThisFileDirectory)Bugzilla22229.xaml">
@ -1004,6 +1007,9 @@
    </EmbeddedResource>
    <EmbeddedResource Include="$(MSBuildThisFileDirectory)VisualControlsPage.xaml">
      <SubType>Designer</SubType>
+       <Generator>MSBuild:UpdateDesignTimeXaml</Generator>
+    </EmbeddedResource>
+    <EmbeddedResource Include="$(MSBuildThisFileDirectory)Issue4356.xaml">
      <Generator>MSBuild:UpdateDesignTimeXaml</Generator>
    </EmbeddedResource>
  </ItemGroup>
--- a/Xamarin.Forms.Platform.iOS/Renderers/ListViewRenderer.cs
+++ b/Xamarin.Forms.Platform.iOS/Renderers/ListViewRenderer.cs
@ -19,7 +19,6 @@ namespace Xamarin.Forms.Platform.iOS
 	{
 		const int DefaultRowHeight = 44;
 		ListViewDataSource _dataSource;
-		bool _estimatedRowHeight;
 		IVisualElementRenderer _headerRenderer;
 		IVisualElementRenderer _footerRenderer;

@ -66,7 +65,7 @@ namespace Xamarin.Forms.Platform.iOS
 				// You will remove it and test and find everything is fiiiiiine, but it is not fine, no it is far from fine. See iOS, or at least iOS 8
 				// has an issue where-by if the TableHeaderView happens to NOT be an integer height, it will add padding to the space between the content
 				// of the UITableView and the TableHeaderView to the tune of the difference between Math.Ceiling (height) - height. Now this seems fine
-				// and when you test it will be, EXCEPT that it does this every time you toggle the visibility of the UITableView causing the spacing to 
+				// and when you test it will be, EXCEPT that it does this every time you toggle the visibility of the UITableView causing the spacing to
 				// grow a little each time, which you weren't testing at all were you? So there you have it, the stupid reason we integer align here.
 				//
 				// The same technically applies to the footer, though that could hardly matter less. We just do it for fun.
@ -240,7 +239,6 @@ namespace Xamarin.Forms.Platform.iOS

 				Control.Source = _dataSource = e.NewElement.HasUnevenRows ? new UnevenListViewDataSource(e.NewElement, _tableViewController) : new ListViewDataSource(e.NewElement, _tableViewController);

-				UpdateEstimatedRowHeight();
 				UpdateHeader();
 				UpdateFooter();
 				UpdatePullToRefreshEnabled();
@ -269,7 +267,6 @@ namespace Xamarin.Forms.Platform.iOS
 				_dataSource.UpdateGrouping();
 			else if (e.PropertyName == Xamarin.Forms.ListView.HasUnevenRowsProperty.PropertyName)
 			{
-				_estimatedRowHeight = false;
 				Control.Source = _dataSource = Element.HasUnevenRows ? new UnevenListViewDataSource(_dataSource) : new ListViewDataSource(_dataSource);
 				ReloadData();
 			}
@ -396,39 +393,6 @@ namespace Xamarin.Forms.Platform.iOS
 			}
 		}

-		void UpdateEstimatedRowHeight()
-		{
-			if (_estimatedRowHeight)
-				return;
-
-			// 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()
 		{
@ -448,7 +412,7 @@ namespace Xamarin.Forms.Platform.iOS
 						return;
 					}
 					Control.TableFooterView = null;
-					
+
 					_footerRenderer.Element?.DisposeModalAndChildRenderers();
 					_footerRenderer.Dispose();
 					_footerRenderer = null;
@ -554,8 +518,6 @@ namespace Xamarin.Forms.Platform.iOS
 			switch (e.Action)
 			{
 				case NotifyCollectionChangedAction.Add:
-
-					UpdateEstimatedRowHeight();
 					if (e.NewStartingIndex == -1 || groupReset)
 						goto case NotifyCollectionChangedAction.Reset;

@ -569,7 +531,7 @@ namespace Xamarin.Forms.Platform.iOS

 					DeleteRows(e.OldStartingIndex, e.OldItems.Count, section);

-					if (_estimatedRowHeight && TemplatedItemsView.TemplatedItems.Count == 0)
+					if (TemplatedItemsView.TemplatedItems.Count == 0)
 						InvalidateCellCache();

 					break;
@ -580,7 +542,7 @@ namespace Xamarin.Forms.Platform.iOS

 					MoveRows(e.NewStartingIndex, e.OldStartingIndex, e.OldItems.Count, section);

-					if (_estimatedRowHeight && e.OldStartingIndex == 0)
+					if (e.OldStartingIndex == 0)
 						InvalidateCellCache();

 					break;
@ -591,7 +553,7 @@ namespace Xamarin.Forms.Platform.iOS

 					ReloadRows(e.OldStartingIndex, e.OldItems.Count, section);

-					if (_estimatedRowHeight && e.OldStartingIndex == 0)
+					if (e.OldStartingIndex == 0)
 						InvalidateCellCache();

 					break;
@ -685,7 +647,6 @@ namespace Xamarin.Forms.Platform.iOS

 		void InvalidateCellCache()
 		{
-			_estimatedRowHeight = false;
 			_dataSource.InvalidatePrototypicalCellCache();
 		}

@ -711,7 +672,7 @@ namespace Xamarin.Forms.Platform.iOS
 		void UpdateSeparatorColor()
 		{
 			var color = Element.SeparatorColor;
-			// ...and Steve said to the unbelievers the separator shall be gray, and gray it was. The unbelievers looked on, and saw that it was good, and 
+			// ...and Steve said to the unbelievers the separator shall be gray, and gray it was. The unbelievers looked on, and saw that it was good, and
 			// they went forth and documented the default color. The holy scripture still reflects this default.
 			// Defined here: https://developer.apple.com/library/ios/documentation/UIKit/Reference/UITableView_Class/#//apple_ref/occ/instp/UITableView/separatorColor
 			Control.SeparatorColor = color.ToUIColor(UIColor.Gray);
@ -751,7 +712,7 @@ namespace Xamarin.Forms.Platform.iOS
 			if (_tableViewController != null)
 				_tableViewController.UpdateRefreshControlColor(color == Color.Default ? null : color.ToUIColor());
    }
-    
+
 		void UpdateVerticalScrollBarVisibility()
 		{
 			if (_defaultVerticalScrollVisibility == null)
@ -804,7 +765,7 @@ namespace Xamarin.Forms.Platform.iOS
 			{
 			}

-			internal nfloat GetEstimatedRowHeight(UITableView table)
+			nfloat GetEstimatedRowHeight(UITableView table)
 			{
 				if (List.RowHeight != -1)
 				{
@ -840,7 +801,7 @@ namespace Xamarin.Forms.Platform.iOS
 					// we don't need to use estimatedRowHeight at all; zero will disable it and use the known heights.
 					// However, not setting the EstimatedRowHeight will drastically degrade performance with large lists.
 					// In this case, we will cache the specified cell heights asynchronously, which will be returned one time on
-					// table load by EstimatedHeight. 
+					// table load by EstimatedHeight.

 					return 0;
 				}
@ -848,12 +809,21 @@ namespace Xamarin.Forms.Platform.iOS
 				return CalculateHeightForCell(table, firstCell);
 			}

-			internal override void InvalidatePrototypicalCellCache()
+			internal override void InvalidatingPrototypicalCellCache()
 			{
 				ClearPrototype();
 				_prototypicalCellByTypeOrDataTemplate.Clear();
 			}

+			protected override void UpdateEstimatedRowHeight(UITableView tableView)
+			{
+				var estimatedRowheight  = GetEstimatedRowHeight(tableView);
+				//if we are providing 0 we are disabling EstimatedRowHeight,
+				//this works fine on newer versions, but iOS10 it will cause a crash so we leave the default value
+				if (estimatedRowheight == 0 && Forms.IsiOS11OrNewer)
+					tableView.EstimatedRowHeight = estimatedRowheight;
+			}
+
 			internal Cell GetPrototypicalCell(NSIndexPath indexPath)
 			{
 				var itemTypeOrDataTemplate = default(object);
@ -976,6 +946,9 @@ namespace Xamarin.Forms.Platform.iOS
 			bool _isDragging;
 			bool _selectionFromNative;
 			bool _disposed;
+			bool _wasEmpty;
+			bool _estimatedRowHeight;
+
 			public UITableViewRowAnimation ReloadSectionsAnimation { get; set; } = UITableViewRowAnimation.Automatic;

 			public ListViewDataSource(ListViewDataSource source)
@ -1003,12 +976,15 @@ namespace Xamarin.Forms.Platform.iOS

 			public Dictionary<int, int> Counts { get; set; }

-			UIColor DefaultBackgroundColor
+			UIColor DefaultBackgroundColor => UIColor.Clear;
+
+			internal void InvalidatePrototypicalCellCache()
 			{
-				get { return UIColor.Clear; }
+				_estimatedRowHeight = false;
+				InvalidatingPrototypicalCellCache();
 			}

-			internal virtual void InvalidatePrototypicalCellCache()
+			internal virtual void InvalidatingPrototypicalCellCache()
 			{
 			}

@ -1197,12 +1173,28 @@ namespace Xamarin.Forms.Platform.iOS
 				List.NotifyRowTapped(indexPath.Section, indexPath.Row, formsCell);
 			}

+			public override void WillDisplay(UITableView tableView, UITableViewCell cell, NSIndexPath indexPath)
+			{
+				if (!_estimatedRowHeight)
+				{
+					// Our cell size/estimate is out of date, probably because we moved from zero to one item; update it
+					DetermineEstimatedRowHeight();
+				}
+			}
+
 			public override nint RowsInSection(UITableView tableview, nint section)
 			{
 				int countOverride;
 				if (Counts.TryGetValue((int)section, out countOverride))
 				{
 					Counts.Remove((int)section);
+					if (_wasEmpty && countOverride > 0)
+					{
+						// We've moved from no items to having at least one item; it's likely that the layout needs to update
+						// its cell size/estimate
+						_estimatedRowHeight = false;
+					}
+					_wasEmpty = countOverride == 0;
 					return countOverride;
 				}

@ -1261,6 +1253,16 @@ namespace Xamarin.Forms.Platform.iOS
 					PerformWithoutAnimation(() => { _uiTableView.ReloadData(); });
 			}

+			public void DetermineEstimatedRowHeight()
+			{
+				if (_estimatedRowHeight)
+					return;
+
+				UpdateEstimatedRowHeight(_uiTableView);
+
+				_estimatedRowHeight = true;
+			}
+
 			protected bool IsValidIndexPath(NSIndexPath indexPath)
 			{
 				var templatedItems = TemplatedItemsView.TemplatedItems;
@ -1369,6 +1371,19 @@ namespace Xamarin.Forms.Platform.iOS
 				}
 			}

+			protected virtual void UpdateEstimatedRowHeight(UITableView tableView)
+			{
+
+				// 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
+				tableView.EstimatedRowHeight = DefaultRowHeight;
+
+				// if even rows OR uneven rows but user specified a row height anyway...
+				if (!List.HasUnevenRows || List.RowHeight != -1)
+					tableView.EstimatedRowHeight = 0;
+			}
+
 			protected override void Dispose(bool disposing)
 			{
 				if (_disposed)
@ -1434,9 +1449,9 @@ namespace Xamarin.Forms.Platform.iOS
 		internal bool _usingLargeTitles;
 		bool _isRefreshing;

-		public FormsUITableViewController(ListView element, bool usingLargeTitles) 
-		: base(element.OnThisPlatform().GetGroupHeaderStyle() == GroupHeaderStyle.Plain 
-			? UITableViewStyle.Plain 
+		public FormsUITableViewController(ListView element, bool usingLargeTitles)
+		: base(element.OnThisPlatform().GetGroupHeaderStyle() == GroupHeaderStyle.Plain
+			? UITableViewStyle.Plain
 			  : UITableViewStyle.Grouped)
 		{
 			if (Forms.IsiOS9OrNewer)
@ -1463,7 +1478,7 @@ namespace Xamarin.Forms.Platform.iOS
 				{
 					_refresh.BeginRefreshing();

-					//hack: On iOS11 with large titles we need to adjust the scroll offset manually 
+					//hack: On iOS11 with large titles we need to adjust the scroll offset manually
 					//since our UITableView is not the first child of the UINavigationController
 					UpdateContentOffset(TableView.ContentOffset.Y - _refresh.Frame.Height);

@ -1499,7 +1514,7 @@ namespace Xamarin.Forms.Platform.iOS
 				}
 			}
 			// https://bugzilla.xamarin.com/show_bug.cgi?id=52962
-			// just because pullToRefresh is being disabled does not mean we should kill an in progress refresh. 
+			// just because pullToRefresh is being disabled does not mean we should kill an in progress refresh.
 			// Consider the case where:
 			//   1. User pulls to refresh
 			//   2. App RefreshCommand fires (at this point _refresh.Refreshing is true)
@ -1509,7 +1524,7 @@ namespace Xamarin.Forms.Platform.iOS
 			//   5. We end up here; A refresh is in progress while being asked to disable pullToRefresh
 		}

-		//hack: Form some reason UIKit isn't allowing to scroll negative values with largetitles 
+		//hack: Form some reason UIKit isn't allowing to scroll negative values with largetitles
 		public void ForceRefreshing()
 		{
 			if (!_list.IsPullToRefreshEnabled)
@ -1543,6 +1558,11 @@ namespace Xamarin.Forms.Platform.iOS
 			UpdateIsRefreshing(true);
 		}

+		public override void ViewWillLayoutSubviews()
+		{
+			(TableView?.Source as ListViewRenderer.ListViewDataSource)?.DetermineEstimatedRowHeight();
+		}
+
 		public void UpdateRefreshControlColor(UIColor color)
 		{
 			if (RefreshControl != null)
@ -1610,7 +1630,6 @@ namespace Xamarin.Forms.Platform.iOS
 		}
 	}

-
 	public class FormsRefreshControl : UIRefreshControl
 	{
 		bool _usingLargeTitles;
@ -1628,7 +1647,7 @@ namespace Xamarin.Forms.Platform.iOS
 			}
 			set
 			{
-				//hack: ahahah take that UIKit! 
+				//hack: ahahah take that UIKit!
 				//when using pull to refresh with Large tiles sometimes iOS tries to hide the UIRefreshControl
 				if (_usingLargeTitles && value && Refreshing)
 					return;