[iOS] If the UITableView hasn't rendered anything yet don't try to sync cells (#3090) fixes #1342 fixes #1542 fixes #1927

* [iOS] fixes #1342 - verify the UITableView has rendered cells before trying to synchronize to collection

* - let reset through on CollectionChanged

Xamarin.Forms.Controls.Issues/Xamarin.Forms.Controls.Issues.Shared/Issue1342.cs

@@ -0,0 +1,170 @@
+using System;
+using System.Collections.Generic;
+using System.Collections.ObjectModel;
+using System.ComponentModel;
+using System.Text;
+using System.Windows.Input;
+using Xamarin.Forms.CustomAttributes;
+using Xamarin.Forms.Internals;
+
+
+#if UITEST
+using Xamarin.UITest;
+using NUnit.Framework;
+using Xamarin.Forms.Core.UITests;
+#endif
+
+namespace Xamarin.Forms.Controls.Issues
+{
+	[Preserve(AllMembers = true)]
+	[Issue(IssueTracker.Github, 1342, "[iOS] ListView throws Exception on ObservableCollection.Add/Remove for non visible list view",
+		PlatformAffected.iOS)]
+#if UITEST
+	[NUnit.Framework.Category(UITestCategories.ListView)]
+#endif
+	public class Issue1342 : TestNavigationPage
+	{
+		const string add2 = "add2";
+		const string add3 = "add3";
+		const string success = "No crash means success";
+
+		protected override void Init()
+		{
+			PushAsync(new MainPageCode
+			{
+				BindingContext = new MainViewModel
+				{
+					ViewModel1 = new ListViewModel
+					{
+						Items = new ObservableCollection<string>(new[] { $"Click {add2}", $"Click {add3}", success })
+					},
+					ViewModel2 = new ListViewModel
+					{
+						Items = new ObservableCollection<string>(new[] { "item2.1", "item2.2", "item2.3" })
+					},
+					ViewModel3 = new ListViewModel
+					{
+						Items = new ObservableCollection<string>()
+					}
+				}
+			});
+		}
+
+		[Preserve(AllMembers = true)]
+		public partial class MainPageCode : TabbedPage
+		{
+			public MainPageCode()
+			{
+				ToolbarItems.Add(new Xamarin.Forms.ToolbarItem() { Text = "add1" });
+				ToolbarItems.Add(new Xamarin.Forms.ToolbarItem() { Text = $"{add2}" });
+				ToolbarItems.Add(new Xamarin.Forms.ToolbarItem() { Text = $"{add3}" });
+				ToolbarItems.Add(new Xamarin.Forms.ToolbarItem() { Text = "reload" });
+				ToolbarItems.Add(new Xamarin.Forms.ToolbarItem() { Text = "visible" });
+
+
+				ToolbarItems[0].SetBinding(ToolbarItem.CommandProperty, "Add1Command");
+				ToolbarItems[1].SetBinding(ToolbarItem.CommandProperty, "Add2Command");
+				ToolbarItems[2].SetBinding(ToolbarItem.CommandProperty, "Add3Command");
+				ToolbarItems[3].SetBinding(ToolbarItem.CommandProperty, "Add4Command");
+				ToolbarItems[4].SetBinding(ToolbarItem.CommandProperty, "Add5Command");
+
+				ListPageCode page = new ListPageCode();
+				page.SetBinding(ListPageCode.BindingContextProperty, "ViewModel1");
+				Children.Add(page);
+
+				page = new ListPageCode();
+				page.SetBinding(ListPageCode.BindingContextProperty, "ViewModel2");
+				Children.Add(page);
+
+				page = new ListPageCode();
+				page.SetBinding(ListPageCode.BindingContextProperty, "ViewModel3");
+				Children.Add(page);
+			}
+		}
+
+		[Preserve(AllMembers = true)]
+		public class MainViewModel
+		{
+
+			void AddItems(ObservableCollection<string> list)
+			{
+				list.Add("new item");
+			}
+
+			public MainViewModel()
+			{
+				Add1Command = new Command(() => AddItems(ViewModel1.Items));
+				Add2Command = new Command(() => AddItems(ViewModel2.Items));
+				Add3Command = new Command(() => AddItems(ViewModel3.Items));
+				Add4Command = new Command(() =>
+				{
+					ViewModel1.ReloadData();
+					ViewModel2.ReloadData();
+					ViewModel3.ReloadData();
+				});
+				Add5Command = new Command(() =>
+				{
+					ViewModel1.ChangeListViewVisability();
+					ViewModel2.ChangeListViewVisability();
+					ViewModel3.ReloadData();
+				});
+			}
+
+			public ListViewModel ViewModel1 { get; set; }
+			public ListViewModel ViewModel2 { get; set; }
+			public ListViewModel ViewModel3 { get; set; }
+
+			public ICommand Add1Command { get; }
+			public ICommand Add2Command { get; }
+			public ICommand Add3Command { get; }
+			public ICommand Add4Command { get; }
+			public ICommand Add5Command { get; }
+		}
+
+		[Preserve(AllMembers = true)]
+		public class ListViewModel : INotifyPropertyChanged
+		{
+			public ObservableCollection<string> Items { get; set; }
+			public bool IsVisible { get; set; } = true;
+
+			public event PropertyChangedEventHandler PropertyChanged;
+
+			public void ReloadData()
+			{
+				Items = new ObservableCollection<string>();
+				PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(nameof(Items)));
+			}
+
+			public void ChangeListViewVisability()
+			{
+				IsVisible = !IsVisible;
+				PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(nameof(IsVisible)));
+
+			}
+		}
+
+		[Preserve(AllMembers = true)]
+		public partial class ListPageCode : ContentPage
+		{
+			public ListPageCode()
+			{
+				Icon = "coffee.png";
+				ListView view = new ListView(ListViewCachingStrategy.RecycleElement);
+				Content = view;
+
+				view.SetBinding(ListView.ItemsSourceProperty, "Items");
+				view.SetBinding(ListView.IsVisibleProperty, "IsVisible");
+			}
+		}
+
+#if UITEST
+		[Test]
+		public void AddingItemsToNonVisibleListViewDoesntCrash()
+		{
+			RunningApp.Tap(add2);
+			RunningApp.Tap(add3);
+			RunningApp.WaitForElement(success);
+		}
+#endif
+	}
+}

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

@@ -244,6 +244,7 @@
     <Compile Include="$(MSBuildThisFileDirectory)Issue1799.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Issue1931.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Issue3089.cs" />
+    <Compile Include="$(MSBuildThisFileDirectory)Issue1342.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Issue2767.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Issue2499.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)GitHub1878.cs" />

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

@@ -530,6 +530,11 @@ namespace Xamarin.Forms.Platform.iOS
 			if (exArgs != null)
 				_dataSource.Counts[section] = exArgs.Count;
 
+			// This means the UITableView hasn't rendered any cells yet
+			// so there's no need to synchronize the rows on the UITableView
+			if (Control.IndexPathsForVisibleRows == null && e.Action != NotifyCollectionChangedAction.Reset)
+				return;
+
 			var groupReset = resetWhenGrouped && Element.IsGroupingEnabled;
 
 			// We can't do this check on grouped lists because the index doesn't match the number of rows in a section.