fix(ListView): unnecessary SelectTemplate call on collection reset

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

@@ -40,6 +40,12 @@ public partial class Given_ListViewBase // resources
 	{
 		private ResourceDictionary _testsResources;
 
+		[TestInitialize]
+		public void Init()
+		{
+			_testsResources = new TestsResources();
+		}
+
 		private Style BasicContainerStyle => _testsResources["BasicListViewContainerStyle"] as Style;
 
 		private Style ContainerMarginStyle => _testsResources["ListViewContainerMarginStyle"] as Style;
@@ -88,12 +94,6 @@ public partial class Given_ListViewBase // resources
 #endif
 	public partial class Given_ListViewBase // test cases
 	{
-		[TestInitialize]
-		public void Init()
-		{
-			_testsResources = new TestsResources();
-		}
-
 		[TestMethod]
 		[RunsOnUIThread]
 		public void ValidSelectionChange()
@@ -2803,6 +2803,41 @@ bool IsVisible(object x) => x is UIElement uie
 				: false;
 #endif
 		}
+
+		[TestMethod]
+		public async Task When_ItemsSource_INCC_Reset()
+		{
+			// note: In order to repro #12059 (extra SelectTemplate call) & SelectTemplateCore called with incorrect item (the `source` is passed as item),
+			// we need a binding that inherits source from DataContext, and not: new Binding { Source = source }, or direct assignment.
+			Action<object> onSelectTemplateHook = null;
+
+			var source = new ObservableCollection<object>(new[] { new object() });
+			var sut = new ListView
+			{
+				ItemTemplateSelector = new LambdaDataTemplateSelector(x =>
+				{
+					onSelectTemplateHook?.Invoke(x);
+					return TextBlockItemTemplate;
+				}),
+			};
+			sut.DataContext = source;
+			sut.SetBinding(ItemsControl.ItemsSourceProperty, new Binding());
+
+			WindowHelper.WindowContent = sut;
+			await WindowHelper.WaitForLoaded(sut);
+			await WindowHelper.WaitForIdle();
+
+			// Clearing the source SHOULD NOT cause the ItemTemplateSelector to be re-evaluated,
+			// especially so when we are leaving the source empty.
+			var wasSelectTemplateCalled = false;
+			onSelectTemplateHook = x => wasSelectTemplateCalled = true;
+			source.Clear();
+
+			if (wasSelectTemplateCalled)
+			{
+				Assert.Fail("DataTemplateSelector.SelectTemplateCore is invoked during an INCC reset.");
+			}
+		}
 	}
 
 	public partial class Given_ListViewBase // data class, data-context, view-model, template-selector
@@ -3035,6 +3070,19 @@ public string Display
 				set => SetAndRaiseIfChanged(ref _display, value);
 			}
 		}
+
+		public class LambdaDataTemplateSelector : DataTemplateSelector
+		{
+			private readonly Func<object, DataTemplate> _impl;
+
+			public LambdaDataTemplateSelector(Func<object, DataTemplate> impl)
+			{
+				this._impl = impl;
+			}
+
+			protected override DataTemplate SelectTemplateCore(object item, DependencyObject container) => SelectTemplateCore(item);
+			protected override DataTemplate SelectTemplateCore(object item) => _impl(item);
+		}
 	}
 
 	public partial class Given_ListViewBase // helpers

src/Uno.UI/UI/Xaml/Controls/ItemsControl/ItemsControl.cs

@@ -1171,8 +1171,6 @@ internal void CleanUpContainer(global::Windows.UI.Xaml.DependencyObject element)
 			}
 			else if (element is ContentControl contentControl)
 			{
-				contentControl.ClearValue(DataContextProperty);
-
 				if (!isOwnContainer)
 				{
 					static void ClearPropertyWhenNoExpression(ContentControl target, DependencyProperty property)
@@ -1201,6 +1199,10 @@ static void ClearPropertyWhenNoExpression(ContentControl target, DependencyPrope
 						ClearPropertyWhenNoExpression(contentControl, ContentControl.ContentTemplateSelectorProperty);
 					}
 				}
+
+				// We are clearing the DataContext last. Because if there is a binding set on any of the above properties, Content(Template(Selector)?)?,
+				// clearing the DC can cause the data-bound property to be unnecessarily re-evaluated with an inherited DC from the visual parent.
+				contentControl.ClearValue(DataContextProperty);
 			}
 		}