[Android] CarouselView: VirtualView cannot be null here, when clearin…

…g and adding items on second navigation - fix (#22207)

* Fix #22035

* Added UITest

* Updated test

* Updated test

* Updated test

* Updated test

* - small change to code and fix test

* Update Issue22035.cs

* Update Issue22035.cs

* - fix test

* - fix test

---------

Co-authored-by: Javier Suárez <javiersuarezruiz@hotmail.com>
Co-authored-by: Shane Neuville <shneuvil@microsoft.com>
Co-authored-by: Shane Neuville <shane94@hotmail.com>

src/Controls/samples/Controls.Sample.UITests/Issues/Issue22035.xaml

@@ -0,0 +1,20 @@
+<?xml version="1.0" encoding="utf-8" ?>
+<ContentPage 
+  xmlns="http://schemas.microsoft.com/dotnet/2021/maui"  
+  xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
+  x:Class="Maui.Controls.Sample.Issues.Issue22035Page1">
+  <VerticalStackLayout   
+    Spacing="25"
+    Padding="30,0"
+    VerticalOptions="Center">
+    <Label 
+      Text="Navigate to the page with the CarouselView several times. If the CarouselView always loads items without exceptions, the test passes."/>
+    <Button
+      x:Name="NavigateBtn"
+      AutomationId="TestNavigateButton"
+      Text="Go to CarouselView"
+      SemanticProperties.Hint="Goes to page with CarouselView"
+      Clicked="OnNavigateClicked"
+      HorizontalOptions="Center" />
+  </VerticalStackLayout>
+</ContentPage>

src/Controls/samples/Controls.Sample.UITests/Issues/Issue22035.xaml.cs

@@ -0,0 +1,30 @@
+using System;
+using Microsoft.Maui.Controls;
+using Microsoft.Maui.Controls.Xaml;
+
+namespace Maui.Controls.Sample.Issues
+{
+	[XamlCompilation(XamlCompilationOptions.Compile)]
+	[Issue(IssueTracker.Github, 22035, "[Android] CarouselView: VirtualView cannot be null here, when clearing and adding items on second navigation", PlatformAffected.Android)]
+	public class Issue22035 : NavigationPage
+	{
+		public Issue22035() : base(new Issue22035Page1())
+		{
+
+		}
+	}
+
+	public partial class Issue22035Page1 : ContentPage
+	{
+		Issue22035Page2 _Issue22035Page2 = new Issue22035Page2();
+		public Issue22035Page1()
+		{
+			InitializeComponent();
+		}
+
+		async void OnNavigateClicked(object sender, EventArgs e)
+		{
+			await Navigation.PushAsync(_Issue22035Page2);
+		}
+	}
+}

src/Controls/samples/Controls.Sample.UITests/Issues/Issue22035Page2.xaml

@@ -0,0 +1,34 @@
+<?xml version="1.0" encoding="utf-8" ?>
+<ContentPage 
+  xmlns="http://schemas.microsoft.com/dotnet/2021/maui"
+  xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
+  x:Class="Maui.Controls.Sample.Issues.Issue22035Page2"
+  xmlns:local="clr-namespace:Maui.Controls.Sample.Issues">
+  <Grid RowDefinitions="Auto,*">
+    <Button
+      Grid.Row="0"
+      AutomationId="TestLoadButton"
+      Text="Load Items"     
+      Pressed="OnLoadButtonPressed" />
+    <CarouselView 
+      Grid.Row="1"
+      ItemsSource="{Binding Images}" 
+      MaximumHeightRequest="150">
+      <CarouselView.ItemTemplate>
+        <DataTemplate x:DataType="local:Issue22035Model">
+          <Grid
+            RowDefinitions="*, Auto">
+            <Image 
+              Source="{Binding ImagePath}"
+              AutomationId="{Binding AutomationId}" />
+            <Label 
+              Grid.Row="1"
+              HorizontalOptions="Center"
+              AutomationId="{Binding AutomationId}"
+              Text="{Binding Text}"/>
+          </Grid>
+        </DataTemplate>
+      </CarouselView.ItemTemplate>
+    </CarouselView>
+  </Grid>
+</ContentPage>

src/Controls/samples/Controls.Sample.UITests/Issues/Issue22035Page2.xaml.cs

@@ -0,0 +1,38 @@
+using System;
+using System.Collections.ObjectModel;
+using System.Threading.Tasks;
+using Microsoft.Maui.Controls;
+using Microsoft.Maui.Controls.Xaml;
+
+namespace Maui.Controls.Sample.Issues
+{
+	[XamlCompilation(XamlCompilationOptions.Compile)]
+	public partial class Issue22035Page2 : ContentPage
+	{
+		public Issue22035Page2()
+		{
+			InitializeComponent();
+
+			BindingContext = this;
+		}
+
+		public ObservableCollection<Issue22035Model> Images { get; set; } = new();
+
+		void OnLoadButtonPressed(object sender, EventArgs e)
+		{
+			Images.Clear();
+
+			Images.Add(new Issue22035Model { Text = "Item 1", ImagePath = "photo21314.jpg" });
+			Images.Add(new Issue22035Model { Text = "Item 2", ImagePath = "oasis.jpg" });
+			Images.Add(new Issue22035Model { Text = "Item 3", ImagePath = "photo21314.jpg" });
+			Images.Add(new Issue22035Model { Text = "Item 4", ImagePath = "oasis.jpg" });
+		}
+	}
+
+	public class Issue22035Model
+	{
+		public string Text { get; set; }
+		public string ImagePath { get; set; }
+		public string AutomationId => Text.Replace(" ", "", StringComparison.InvariantCultureIgnoreCase);
+	}
+}

src/Controls/src/Core/Handlers/Items/Android/MauiCarouselRecyclerView.cs

@@ -101,10 +101,11 @@ public override void SetUpNewElement(CarouselView newElement)
 
 		public override void TearDownOldElement(CarouselView oldElement)
 		{
-			if (ItemsView != null)
+			if (ItemsView is not null)
 				ItemsView.Scrolled -= CarouselViewScrolled;
 
 			ClearLayoutListener();
+			UnsubscribeCollectionItemsSourceChanged(ItemsViewAdapter);
 			base.TearDownOldElement(oldElement);
 		}
 

src/Controls/tests/UITests/Tests/Issues/Issue22035.cs

@@ -0,0 +1,35 @@
+using NUnit.Framework;
+using UITest.Appium;
+using UITest.Core;
+
+namespace Microsoft.Maui.AppiumTests.Issues
+{
+	[Category(UITestCategories.CarouselView)]
+	public class Issue22035 : _IssuesUITest
+	{
+		public Issue22035(TestDevice device) : base(device)
+		{
+		}
+
+		public override string Issue => "[Android] CarouselView: VirtualView cannot be null here, when clearing and adding items on second navigation";
+
+		[Test]
+		public void CarouselViewVirtualViewNotNull()
+		{
+			this.IgnoreIfPlatforms(new TestDevice[] { TestDevice.iOS, TestDevice.Mac, TestDevice.Windows },
+				"This test is failing, likely due to product issue. More information: https://github.com/dotnet/maui/issues/22287");
+
+			for (int i = 0; i < 2; i++)
+			{
+				App.WaitForElement("TestNavigateButton");
+				App.Tap("TestNavigateButton");
+				App.WaitForElement("TestLoadButton");
+				App.Tap("TestLoadButton");
+				App.WaitForElement("Item1");
+				App.Back();
+			}
+
+			// Without exceptions, the test has passed.
+		}
+	}
+}