From 656835123b3a2c7257fd321fce87c5f49e6590c0 Mon Sep 17 00:00:00 2001
From: "E.Z. Hart" <hartez@users.noreply.github.com>
Date: Tue, 3 Sep 2019 11:03:16 -0600
Subject: [PATCH] Verify sections exist before calling NumberOfItemsInSection;
 fixes #7338 (#7354)

fixes #7338
---
 .../Issue7338.cs                                   | 71 ++++++++++++++++++++++
 .../Xamarin.Forms.Controls.Issues.Shared.projitems |  3 +-
 .../CollectionView/GridViewLayout.cs               |  6 ++
 3 files changed, 79 insertions(+), 1 deletion(-)
 create mode 100644 Xamarin.Forms.Controls.Issues/Xamarin.Forms.Controls.Issues.Shared/Issue7338.cs

diff --git a/Xamarin.Forms.Controls.Issues/Xamarin.Forms.Controls.Issues.Shared/Issue7338.cs b/Xamarin.Forms.Controls.Issues/Xamarin.Forms.Controls.Issues.Shared/Issue7338.cs
new file mode 100644
index 0000000..1f422d8
--- /dev/null
+++ b/Xamarin.Forms.Controls.Issues/Xamarin.Forms.Controls.Issues.Shared/Issue7338.cs
@@ -0,0 +1,71 @@
+using System;
+using System.Collections.Generic;
+using Xamarin.Forms.CustomAttributes;
+using Xamarin.Forms.Internals;
+
+#if UITEST
+using Xamarin.Forms.Core.UITests;
+using Xamarin.UITest;
+using NUnit.Framework;
+#endif
+
+
+namespace Xamarin.Forms.Controls.Issues
+{
+#if UITEST
+	[Category(UITestCategories.CollectionView)]
+#endif
+	[Preserve(AllMembers = true)]
+	[Issue(IssueTracker.Github, 7338, "[Bug] CollectionView crash if source is empty in XF 4.2.0.709249",
+		PlatformAffected.iOS)]
+	class Issue7338 : TestNavigationPage
+	{
+		const string Success = "success";
+
+		protected override void Init()
+		{
+			FlagTestHelpers.SetCollectionViewTestFlag();
+			PushAsync(CreateRoot());
+		}
+
+		Page CreateRoot()
+		{
+			var page = new ContentPage() { Title = "Issue7338" };
+
+			var instructions = new Label { AutomationId = Success, Text = "If you can see this label, the test has passed." };
+
+			var layout = new StackLayout();
+
+			var cv = new CollectionView
+			{
+				ItemsLayout = new GridItemsLayout(orientation: ItemsLayoutOrientation.Horizontal),
+				ItemTemplate = new DataTemplate(() =>
+				{
+					return Template();
+				})
+			};
+
+			layout.Children.Add(instructions);
+			layout.Children.Add(cv);
+
+			page.Content = layout;
+
+			return page;
+		}
+
+		View Template()
+		{
+			var label1 = new Label { Text = "Text", HeightRequest = 100 };
+			return label1;
+		}
+
+#if UITEST
+		[Test]
+		public void EmptyHorizontalCollectionShouldNotCrash()
+		{
+			// If the instructions are visible at all, then this has succeeded
+			RunningApp.WaitForElement(Success);
+		}
+#endif
+	}
+}
diff --git 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
index f12c343..a466d0e 100644
--- 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
@@ -32,6 +32,7 @@
     <Compile Include="$(MSBuildThisFileDirectory)Issue7049.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Issue7061.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Issue7111.cs" />
+    <Compile Include="$(MSBuildThisFileDirectory)Issue7338.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)ScrollToGroup.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)NestedCollectionViews.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)ShellFlyoutBehavior.cs" />
@@ -1371,4 +1372,4 @@
       <Generator>MSBuild:UpdateDesignTimeXaml</Generator>
     </EmbeddedResource>
   </ItemGroup>
-</Project>
+</Project>
\ No newline at end of file
diff --git a/Xamarin.Forms.Platform.iOS/CollectionView/GridViewLayout.cs b/Xamarin.Forms.Platform.iOS/CollectionView/GridViewLayout.cs
index f8e52e1..b1f07a9 100644
--- a/Xamarin.Forms.Platform.iOS/CollectionView/GridViewLayout.cs
+++ b/Xamarin.Forms.Platform.iOS/CollectionView/GridViewLayout.cs
@@ -138,6 +138,12 @@ namespace Xamarin.Forms.Platform.iOS
 				return false; 
 			}
 
+			if (CollectionView.NumberOfSections() == 0)
+			{
+				// And it only happens if there are items
+				return false;
+			}
+
 			if (EstimatedItemSize.IsEmpty)
 			{
 				// The bug only occurs when using Autolayout; with a set ItemSize, we don't have to worry about it
-- 
2.7.4