Notify child added to CollectionView (#10812) fixes #10454

* Notify child added to CollectionView

* Automate the test

* Fixed merge problem

Co-authored-by: E.Z. Hart <hartez@gmail.com>

Xamarin.Forms.Controls.Issues/Xamarin.Forms.Controls.Issues.Shared/Issue10454.cs

@@ -0,0 +1,105 @@
+using System;
+using System.Collections.ObjectModel;
+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, 10454, "CollectionView ChildAdded", PlatformAffected.All)]
+	public class Issue10454 : TestContentPage
+	{
+		const string Success = "Success";
+
+		protected override void Init()
+		{
+			Title = "Issue 10454";
+
+			BindingContext = new Issue10454ViewModel();
+
+			var layout = new StackLayout();
+
+			var collectionView = new CollectionView();
+			collectionView.SetBinding(ItemsView.ItemsSourceProperty, "Items");
+
+			collectionView.ItemTemplate = new DataTemplate(() =>
+			{
+				var template = new DataTemplate();
+				var content = new Grid
+				{
+					BackgroundColor = Color.LightGray
+				};
+				var label = new Label();
+				label.SetBinding(Label.TextProperty, ".");
+				content.Children.Add(label);
+
+				return content;
+			});
+
+			var labelInfo = new Label
+			{
+				FontSize = 18
+			};
+
+			var successLabel = new Label();
+
+			layout.Children.Add(labelInfo);
+			layout.Children.Add(successLabel);
+			layout.Children.Add(collectionView);
+
+			Content = layout;
+
+			collectionView.ChildAdded += (sender, args) =>
+			{
+				labelInfo.Text = $"ChildAdded {args.Element}";
+				Console.WriteLine(labelInfo.Text);
+
+				successLabel.Text = Success;
+			};
+
+			collectionView.ChildRemoved += (sender, args) =>
+			{
+				labelInfo.Text = $"ChildRemoved  {args.Element}";
+				Console.WriteLine(labelInfo.Text);
+			};
+		}
+
+#if UITEST
+		[Test]
+		public void ChildAddedShouldFire() 
+		{
+			RunningApp.WaitForElement(Success);
+		}
+#endif
+	}
+
+	[Preserve(AllMembers = true)]
+	public class Issue10454ViewModel : BindableObject
+	{
+		public Issue10454ViewModel()
+		{
+			LoadItems();
+		}
+
+		public ObservableCollection<string> Items { get; set; }
+
+		void LoadItems()
+		{
+			Items = new ObservableCollection<string>();
+
+			for (int i = 0; i < 100; i++)
+			{
+				Items.Add($"Item {i+1}");
+			}
+		}
+	}
+}

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

@@ -1499,6 +1499,7 @@
     <Compile Include="$(MSBuildThisFileDirectory)Issue11723.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Issue11496.xaml.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Issue11209.xaml.cs" />
+    <Compile Include="$(MSBuildThisFileDirectory)Issue10454.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Issue11081.xaml.cs" />
   </ItemGroup>
   <ItemGroup>
@@ -2299,4 +2300,4 @@
       <Generator>MSBuild:UpdateDesignTimeXaml</Generator>
     </EmbeddedResource>
   </ItemGroup>
-</Project>
+</Project>

Xamarin.Forms.Core/Items/ItemsView.cs

@@ -97,9 +97,8 @@ public void AddLogicalChild(Element element)
 			}
 
 			_logicalChildren.Add(element);
-
 			element.Parent = this;
-
+			OnChildAdded(element);
 			VisualDiagnostics.OnChildAdded(this, element);
 		}
 
@@ -111,11 +110,13 @@ public void RemoveLogicalChild(Element element)
 			}
 
 			element.Parent = null;
+
 			if (!_logicalChildren.Contains(element))
 				return;
 
 			var oldLogicalIndex = _logicalChildren.IndexOf(element);
 			_logicalChildren.Remove(element);
+			OnChildRemoved(element, oldLogicalIndex);
 			VisualDiagnostics.OnChildRemoved(this, element, oldLogicalIndex);
 		}