[Windows] - CarouselView reverts to displaying 1st item in collection when collection modified

[Mark-NC001]

Description

I have a CarouselView which uses an ObservableCollection<> as it's ItemSource. The CarouselView appears to behave correctly when scrolling through the collection - but if an item gets added to the collection, the CarouselView reverts to showing the first item in the ItemSource collection.

I would have expected the CarouselView to stay on the item that was displayed (unless of course if it gets removed from the underlying collection in ItemSource, in which case I guess showing the first item is valid?).

Android appears to function correctly.

Steps to Reproduce

Create a data type to store. As an example I'm using a Person class:

namespace MauiTestApp.Classes
{
	public class Person
	{
		public string FirstName { get; set; }
	}
}

And a TestPage:

<?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"
             xmlns:classes="clr-namespace:MauiTestApp.Classes;assembly=MauiTestApp"
						 x:Class="MauiTestApp.TestPage">
	<CarouselView x:Name="TheCarouselView">
		<CarouselView.ItemTemplate>
			<DataTemplate x:DataType="classes:Person">
				<StackLayout>
					<Label Text="{Binding FirstName}"  FontAttributes="Bold" />
					<Grid ColumnDefinitions="Auto, Auto, Auto">
						<Button Grid.Column="0" Text="Back" Clicked="OnBack_Clicked" />
						<Button Grid.Column="1" Text="Add" Clicked="OnAdd_Clicked" />
						<Button Grid.Column="2" Text="Next" Clicked="OnNext_Clicked" />
					</Grid>
				</StackLayout>
			</DataTemplate>
		</CarouselView.ItemTemplate>
	</CarouselView>
</ContentPage>

And the code behind:

using MauiTestApp.Classes;
using System.Collections.ObjectModel;

namespace MauiTestApp;

public partial class TestPage : ContentPage
{

	private ObservableCollection<Person> _people = new ObservableCollection<Person>() { new Person() { FirstName = "Person 1" }, new Person() { FirstName = "Person 2" } };

	public TestPage()
	{
		InitializeComponent();
	}
	protected override void OnAppearing()
	{
		base.OnAppearing();

		TheCarouselView.Loop = false;
		TheCarouselView.ItemsSource = _people;
	}

	private void OnAdd_Clicked(object sender, EventArgs e)
	{
		_people.Add(new Person() { FirstName = "Another Person" });
	}

	private void OnBack_Clicked(object sender, EventArgs e)
	{
		int currentIndex = _people.IndexOf(TheCarouselView.CurrentItem as Person);
		if (currentIndex > 0)
			TheCarouselView.ScrollTo(currentIndex - 1);
	}

	private void OnNext_Clicked(object sender, EventArgs e)
	{
		int currentIndex = _people.IndexOf(TheCarouselView.CurrentItem as Person);
		if (currentIndex < _people.Count - 1)
			TheCarouselView.ScrollTo(currentIndex + 1);
	}
}

When showing the page, initially Person 1 is shown, click Next which will move to Person 2. Then click Add - this adds a person called "Another Person". I would have expected Person 2 to still be displayed, but instead Person 1 gets shown.

Link to public reproduction project repository

No response

Version with bug

8.0.93 SR9.3

Is this a regression from previous behavior?

Yes, this used to work in Xamarin.Forms

Last version that worked well

Unknown/Other

Affected platforms

Windows

Affected platform versions

Windows 10.0.19041.0

Did you find any workaround?

No response

Relevant log output

[similar-issues-ai]

We've found some similar issues:

• CarouselView ignores CollectionChanged events of source #17727 , similarity score: 84%

If any of the above are duplicates, please consider closing this issue out and adding additional context in the original issue.

Note: You can give me feedback by 👍 or 👎 this comment.

[Mark-NC001]

Here is a page demonstrating the issue - instructions are included on the page:

using System.Collections.ObjectModel;

namespace MauiTestApp;

public class CarouselViewExample : ContentPage
{

	public class Person
	{
		public string Name { get; set; }
	}

	private ObservableCollection<Person> _collection = new ObservableCollection<Person>() { new Person() { Name = "Person 1" }, new Person() { Name = "Person 2" } };

	private CarouselView MyCarouselView { get; set; }

	public CarouselViewExample()
	{

		StackLayout mainStackLayout = new StackLayout();
		mainStackLayout.Margin = new Thickness(5);

		Label labelInstructions = new Label()
		{
			Text = "Instructions:\nThe CarouselView contains Person 1 and Person 2. It will initially show the first page, Person 1.\n" +
			"Click the 'Scroll to Person 2' button, and the CarouselView will correctly show Person 2.\n" +
			"Click 'Add Person', which will add a new Person record to the collection.\n" +
			"Notice now the CarouselView has jumped back to Person 1!"
		};
		mainStackLayout.Add(labelInstructions);

		MyCarouselView = new CarouselView()
		{
			ItemsSource = _collection,
			Loop = false
		};

		MyCarouselView.ItemTemplate = new DataTemplate(() =>
		{
			StackLayout stackLayout = new StackLayout();
			Label nameLabel = new Label();
			nameLabel.SetBinding(Label.TextProperty, "Name");
			nameLabel.FontSize = 25;
			nameLabel.TextColor = Colors.Red;
			stackLayout.Children.Add(nameLabel);
			return stackLayout;
		});

		mainStackLayout.Add(MyCarouselView);

		Button scrollToPerson2Button = new Button()
		{
			Text = "Scroll to Person 2"
		};
		scrollToPerson2Button.Clicked += ScrollToPerson2Button_Clicked;
		mainStackLayout.Add(scrollToPerson2Button);

		Button addPersonButton = new Button()
		{
			Text = "Add Person",
		};
		addPersonButton.Clicked += AddButton_Clicked;
		mainStackLayout.Add(addPersonButton);

		Content = mainStackLayout;

	}

	private void ScrollToPerson2Button_Clicked(object? sender, EventArgs e)
	{
		MyCarouselView.ScrollTo(1);
	}

	private void AddButton_Clicked(object? sender, EventArgs e)
	{
		_collection.Add(new Person()
		{
			Name = "Person " + (_collection.Count + 1),
		});
	}
}

[Mark-NC001]

Just as an aside, if you omit setting the Loop property to false, clicking the "Scroll to Person 2" button causes the CarouselView to continuously scroll.... another issue...?! Thankfully I don't want it to loop in my use case.

[PureWeen]

@Mark-NC001 can you upload a project to github that we can reproduce this with?

[dotnet-policy-service]

Hi @Mark-NC001. We have added the "s/needs-repro" label to this issue, which indicates that we require steps and sample code to reproduce the issue before we can take further action. Please try to create a minimal sample project/solution or code samples which reproduce the issue, ideally as a GitHub repo that we can clone. See more details about creating repros here: https://github.com/dotnet/maui/blob/main/.github/repro.md

This issue will be closed automatically in 7 days if we do not hear back from you by then - please feel free to re-open it if you come back to this issue after that time.