fix(ListView): [iOS] Ensure that the DataContext propagates properly …

…to Header/Footer

(cherry picked from commit 85e8594)

src/Uno.UI.RuntimeTests/Tests/Windows_UI_Xaml_Controls/Given_ListViewBase.cs

@@ -3022,6 +3022,52 @@ public async Task When_Footer_DataContext()
 			Assert.AreEqual(header2.DataContext.ToString(), header2.Text);
 		}
 
+		[TestMethod]
+		[RunsOnUIThread]
+		public async Task When_HeaderTemplate_DataContext()
+		{
+			TextBlock header = null;
+
+			var SUT = new ListView()
+			{
+				ItemContainerStyle = BasicContainerStyle,
+				HeaderTemplate = new DataTemplate(() =>
+				{
+					var s = new StackPanel
+					{
+						Background = new SolidColorBrush(Colors.Red),
+						Children = {
+							(header = new TextBlock { Text = "empty" }),
+						}
+					};
+
+					header.SetBinding(TextBlock.TextProperty, new Binding { Path = new PropertyPath("MyText") });
+
+					return s;
+				})
+			};
+
+			WindowHelper.WindowContent = SUT;
+			await WindowHelper.WaitForIdle();
+
+			var container = header.FindFirstParent<ContentControl>();
+
+			var source = new[] {
+				new ListViewItem(){ Content = "item 1" },
+			};
+
+			SUT.ItemsSource = source;
+			await WindowHelper.WaitForIdle();
+
+			Assert.IsNull(header.DataContext);
+
+			SUT.DataContext = new When_Header_DataContext_Model("test value");
+			await WindowHelper.WaitForIdle();
+
+			Assert.AreEqual(SUT.DataContext, header.DataContext);
+			Assert.AreEqual("test value", header.Text);
+		}
+
 		private async Task When_Items_Are_Equal_But_Different_References_Common(Selector sut)
 		{
 			var obj1 = new AlwaysEqualClass();

src/Uno.UI/UI/Xaml/Controls/ListViewBase/ListViewBaseSource.iOS.cs

@@ -401,14 +401,24 @@ private UICollectionReusableView GetBindableSupplementaryView(
 						.Binding("Content", "");
 				}
 
+				supplementaryView.Content.ContentTemplate = template;
+
 				if (elementKind == NativeListViewBase.ListViewFooterElementKindNS || elementKind == NativeListViewBase.ListViewHeaderElementKindNS)
 				{
 					supplementaryView.Content.SetParent(Owner.XamlParent);
-					supplementaryView.Content.Content = context;
+
+					if (context is not null)
+					{
+						supplementaryView.Content.Content = context;
+					}
+
+					// We need to reset the DataContext as it may have been forced to null as a local value
+					// during ItemsControl.CleanUpContainer
+					// See https://github.com/unoplatform/uno/blob/54041db0bd6d5049d8efab90b097eaca936bfca1/src/Uno.UI/UI/Xaml/Controls/ItemsControl/ItemsControl.cs#L1200
+					supplementaryView.Content.ClearValue(ContentControl.DataContextProperty);
 				}
 				else
 				{
-					supplementaryView.Content.ContentTemplate = template;
 					supplementaryView.Content.DataContext = context;
 				}