[Android] Handle creating a default GroupHeader if no GroupHeaderTemplate is provided (#248)

Author: rmarinho

Xamarin.Forms.Controls.Issues/Xamarin.Forms.Controls.Issues.Shared/Issue55555.cs

@@ -0,0 +1,88 @@
+using System;
+using System.Collections.ObjectModel;
+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.None, 55555, "Header problem")]
+	public class Issue55555 : TestContentPage // or TestMasterDetailPage, etc ...
+	{
+		protected override void Init()
+		{
+			var lstView = new ListView(ListViewCachingStrategy.RecycleElement);
+			ObservableCollection<GroupedVeggieModel> grouped = CreateData();
+
+			lstView.ItemsSource = grouped;
+			lstView.HasUnevenRows = true;
+			lstView.IsGroupingEnabled = true;
+			lstView.GroupDisplayBinding = new Binding("LongName");
+			lstView.GroupShortNameBinding = new Binding("ShortName");
+
+			lstView.ItemTemplate = new DataTemplate(typeof(DemoTextCell));
+			lstView.ItemTemplate.SetBinding(DemoTextCell.TextProperty, "Name");
+
+			Content = lstView;
+		}
+
+		static ObservableCollection<GroupedVeggieModel> CreateData()
+		{
+			var grouped = new ObservableCollection<GroupedVeggieModel>();
+
+			var veggieGroup = new GroupedVeggieModel() { LongName = "vegetables", ShortName = "v" };
+			veggieGroup.Add(new VeggieModel() { Name = "celery", IsReallyAVeggie = true, Comment = "try ants on a log" });
+			veggieGroup.Add(new VeggieModel() { Name = "tomato", IsReallyAVeggie = false, Comment = "pairs well with basil" });
+			veggieGroup.Add(new VeggieModel() { Name = "zucchini", IsReallyAVeggie = true, Comment = "zucchini bread > bannana bread" });
+			veggieGroup.Add(new VeggieModel() { Name = "peas", IsReallyAVeggie = true, Comment = "like peas in a pod" });
+
+			var fruitGroup = new GroupedVeggieModel() { LongName = "fruit", ShortName = "f" };
+			fruitGroup.Add(new VeggieModel() { Name = "banana", IsReallyAVeggie = false, Comment = "available in chip form factor" });
+			fruitGroup.Add(new VeggieModel() { Name = "strawberry", IsReallyAVeggie = false, Comment = "spring plant" });
+			fruitGroup.Add(new VeggieModel() { Name = "cherry", IsReallyAVeggie = false, Comment = "topper for icecream" });
+
+			grouped.Add(veggieGroup);
+			grouped.Add(fruitGroup);
+
+			return grouped;
+		}
+
+		[Preserve(AllMembers = true)]
+		public class VeggieModel
+		{
+			public string Name { get; set; }
+			public string Comment { get; set; }
+			public bool IsReallyAVeggie { get; set; }
+			public string Image { get; set; }
+		}
+
+		[Preserve(AllMembers = true)]
+		public class GroupedVeggieModel : ObservableCollection<VeggieModel>
+		{
+			public string LongName { get; set; }
+			public string ShortName { get; set; }
+		}
+
+		[Preserve(AllMembers = true)]
+		public class DemoTextCell : TextCell
+		{
+			public DemoTextCell()
+			{
+				Height = 150;
+			}
+		}
+
+#if UITEST
+		[Test]
+		public void TGroupDisplayBindingPresentRecycleElementTest()
+		{
+			RunningApp.WaitForElement(q => q.Marked("vegetables"));
+		}
+#endif
+	}
+}

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

@@ -410,6 +410,7 @@
     <Compile Include="$(MSBuildThisFileDirectory)Bugzilla41038.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Bugzilla38284.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Bugzilla39486.cs" />
+    <Compile Include="$(MSBuildThisFileDirectory)Issue55555.cs" />
   </ItemGroup>
   <ItemGroup>
     <EmbeddedResource Include="$(MSBuildThisFileDirectory)Bugzilla22229.xaml">

Xamarin.Forms.Platform.Android/Renderers/ListViewAdapter.cs

@@ -199,7 +199,7 @@ public override AView GetView(int position, AView convertView, ViewGroup parent)
 
 			if (cachingStrategy == ListViewCachingStrategy.RecycleElement && convertView != null)
 			{
-				var boxedCell = (INativeElementView)convertView;
+				var boxedCell = convertView as INativeElementView;
 				if (boxedCell == null)
 				{
 					throw new InvalidOperationException($"View for cell must implement {nameof(INativeElementView)} to enable recycling.");
@@ -403,20 +403,9 @@ List<Cell> GetCellsFromPosition(int position, int take)
 
 				if (global == position || cells.Count > 0)
 				{
-					if (_listView.CachingStrategy == ListViewCachingStrategy.RecycleElement)
-					{
-						var groupContent = _listView.TemplatedItems.GroupHeaderTemplate?.CreateContent(group.ItemsSource, _listView) as Cell;
-						if (groupContent != null)
-						{
-							groupContent.Parent = _listView;
-							groupContent.BindingContext = group.ItemsSource;
-							cells.Add(groupContent);
-						}
-					}
-					else
-					{
-						cells.Add(group.HeaderContent);
-					}
+					//Always create a new cell if we are using the RecycleElement strategy
+					var headerCell = _listView.CachingStrategy == ListViewCachingStrategy.RecycleElement ? GetNewGroupHeaderCell(group) : group.HeaderContent;
+					cells.Add(headerCell);
 
 					if (cells.Count == take)
 						return cells;
@@ -565,6 +554,26 @@ void UpdateSeparatorColor(bool isHeader, AView bline)
 			}
 		}
 
+		Cell GetNewGroupHeaderCell(ITemplatedItemsList<Cell> group)
+		{
+			var groupHeaderCell = _listView.TemplatedItems.GroupHeaderTemplate?.CreateContent(group.ItemsSource, _listView) as Cell;
+
+			if (groupHeaderCell != null)
+			{
+				groupHeaderCell.BindingContext = group.ItemsSource;
+			}
+			else
+			{
+				groupHeaderCell = new TextCell();
+				groupHeaderCell.SetBinding(TextCell.TextProperty, nameof(group.Name));
+				groupHeaderCell.BindingContext = group;
+			}
+
+			groupHeaderCell.Parent = _listView;
+			groupHeaderCell.SetIsGroupHeader<ItemsView<Cell>, Cell>(true);
+			return groupHeaderCell;
+		}
+
 		enum CellType
 		{
 			Row,