Fix ListView grouping issue on UWP ListView (#14653)

Xamarin.Forms.Controls.Issues/Xamarin.Forms.Controls.Issues.Shared/Issue14095.xaml

@@ -0,0 +1,28 @@
+<?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:d="http://xamarin.com/schemas/2014/forms/design"
+    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
+    mc:Ignorable="d"
+    Title="Test 14095" xmlns:local="using:Xamarin.Forms.Controls"
+    x:Class="Xamarin.Forms.Controls.Issues.Issue14095">
+    <StackLayout
+        Padding="12">
+        <Label
+            Text="If group headers are correct, the test has passed."/>
+        <ListView 
+            x:Name ="lstView" 
+            IsGroupingEnabled="true"
+            GroupDisplayBinding="{Binding LongName}" 
+            GroupShortNameBinding="{Binding ShortName}">
+            <ListView.ItemTemplate>
+                <DataTemplate>
+                    <TextCell
+                        Text="{Binding Name}" 
+                        Detail = "{Binding Comment}" />
+                </DataTemplate>
+            </ListView.ItemTemplate>
+        </ListView>
+    </StackLayout>
+</local:TestContentPage>

Xamarin.Forms.Controls.Issues/Xamarin.Forms.Controls.Issues.Shared/Issue14095.xaml.cs

@@ -0,0 +1,65 @@
+using Xamarin.Forms.CustomAttributes;
+using Xamarin.Forms.Internals;
+using System.Collections.ObjectModel;
+
+#if UITEST
+using Xamarin.UITest;
+using NUnit.Framework;
+using Xamarin.Forms.Core.UITests;
+#endif
+
+namespace Xamarin.Forms.Controls.Issues
+{
+#if UITEST
+	[Category(UITestCategories.ListView)]
+#endif
+	[Preserve(AllMembers = true)]
+	[Issue(IssueTracker.Github, 14095,
+		"[Bug] ListView grouping group names not shown on UWP",
+		PlatformAffected.UWP)]
+	public partial class Issue14095 : TestContentPage
+	{
+		ObservableCollection<GroupedIssue14095Model> Grouped { get; set; }
+
+		public Issue14095()
+		{
+#if APP
+			InitializeComponent();	
+
+			Grouped = new ObservableCollection<GroupedIssue14095Model> ();
+			var veggieGroup = new GroupedIssue14095Model () { LongName = "vegetables", ShortName="v" };
+			var fruitGroup = new GroupedIssue14095Model () { LongName = "fruit", ShortName = "f" };
+			veggieGroup.Add (new Issue14095Model () { Name = "celery", IsReallyAVeggie = true, Comment = "try ants on a log" });
+			veggieGroup.Add (new Issue14095Model () { Name = "tomato", IsReallyAVeggie = false, Comment = "pairs well with basil" });
+			veggieGroup.Add (new Issue14095Model () { Name = "zucchini", IsReallyAVeggie = true, Comment = "zucchini bread > bannana bread" });
+			veggieGroup.Add (new Issue14095Model () { Name = "peas", IsReallyAVeggie = true, Comment = "like peas in a pod" });
+			fruitGroup.Add (new Issue14095Model () {Name = "banana", IsReallyAVeggie = false,Comment = "available in chip form factor"});
+			fruitGroup.Add (new Issue14095Model () {Name = "strawberry", IsReallyAVeggie = false,Comment = "spring plant"});
+			fruitGroup.Add (new Issue14095Model () {Name = "cherry", IsReallyAVeggie = false,Comment = "topper for icecream"});
+
+			Grouped.Add (veggieGroup);
+			Grouped.Add (fruitGroup);
+
+			lstView.ItemsSource = Grouped;
+#endif
+		}
+
+		protected override void Init()
+		{
+		}
+	}
+
+	public class Issue14095Model
+	{
+		public string Name { get; set; }
+		public string Comment { get; set; }
+		public bool IsReallyAVeggie { get; set; }
+		public string Image { get; set; }
+	}
+
+	public class GroupedIssue14095Model : ObservableCollection<Issue14095Model>
+	{
+		public string LongName { get; set; }
+		public string ShortName { get; set; }
+	}
+}

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

@@ -28,6 +28,9 @@
     </Compile>
     <Compile Include="$(MSBuildThisFileDirectory)Issue13819.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Issue13916.cs" />
+    <Compile Include="$(MSBuildThisFileDirectory)Issue14095.xaml.cs">
+      <DependentUpon>Issue14095.xaml</DependentUpon>
+    </Compile>
     <Compile Include="$(MSBuildThisFileDirectory)Issue14523.xaml.cs">
       <DependentUpon>Issue14523.xaml</DependentUpon>
     </Compile>
@@ -2864,4 +2867,10 @@
       <Generator>MSBuild:UpdateDesignTimeXaml</Generator>
     </EmbeddedResource>
   </ItemGroup>
+  <ItemGroup>
+    <EmbeddedResource Include="$(MSBuildThisFileDirectory)Issue14095.xaml">
+      <SubType>Designer</SubType>
+      <Generator>MSBuild:Compile</Generator>
+    </EmbeddedResource>
+  </ItemGroup>
 </Project>

Xamarin.Forms.Platform.UAP/CellControl.cs

@@ -330,17 +330,10 @@ void SetCell(object newContext)
 			// If there is a ListView, load the Cell content from the ItemTemplate.
 			// Otherwise, the given Cell is already a templated Cell from a TableView.
 			ListView lv = _listView.Value;
+
 			if (lv != null)
 			{
-				// 🚀 If there is an old cell, check if it was a group header
-				// we need this later to know whether we can recycle this cell
-				bool? wasGroupHeader = null;
-				var oldCell = Cell;
-				if (oldCell != null)
-				{
-					wasGroupHeader = oldCell.GetIsGroupHeader<ItemsView<Cell>, Cell>();
-				}
-
+				Cell oldCell = Cell;
 				bool isGroupHeader = IsGroupHeader;
 				DataTemplate template = isGroupHeader ? lv.GroupHeaderTemplate : lv.ItemTemplate;
 				object bindingContext = newContext;
@@ -358,15 +351,8 @@ void SetCell(object newContext)
 						sameTemplate = oldTemplate == template;
 					}
 				}
-				// 🚀 if there is no datatemplateselector, we now verify if the old cell
-				// was a groupheader and whether the new one is as well.
-				// Again, this is only to verify we can reuse this cell
-				else if (wasGroupHeader.HasValue)
-				{
-					sameTemplate = wasGroupHeader == isGroupHeader;
-				}
 
-				// reuse cell
+				// Reuse cell
 				var canReuseCell = Cell != null && sameTemplate;
 
 				// 🚀 If we can reuse the cell, just reuse it...
@@ -403,7 +389,8 @@ void SetCell(object newContext)
 
 			if (Cell != cell)
 				Cell = cell;
-			// 🚀 even if the cell did not change, we **must** call SendDisappearing() and SendAppearing()
+
+			// 🚀 Even if the cell did not change, we **must** call SendDisappearing() and SendAppearing()
 			// because frameworks such as Reactive UI rely on this! (this.WhenActivated())
 			else if (Cell != null)
 			{