Nested ItemsRepeater in a ScrollViewer behaves weird

[balthild]

Describe the bug

See the screen recording.

ItemsControl does not have such issue.

To Reproduce

https://github.com/balthild/avalonia-itemsrepeater-issue

<Window xmlns="https://github.com/avaloniaui"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:vm="clr-namespace:itemsrepeaterissue.ViewModels;assembly=itemsrepeaterissue"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        mc:Ignorable="d" d:DesignWidth="800" d:DesignHeight="450"
        x:Class="itemsrepeaterissue.Views.MainWindow"
        Icon="/Assets/avalonia-logo.ico"
        Title="itemsrepeaterissue">

    <Design.DataContext>
        <vm:MainWindowViewModel />
    </Design.DataContext>

    <ScrollViewer HorizontalScrollBarVisibility="Disabled">
        <ItemsRepeater Items="{Binding ItemGroups}" Margin="24">
            <ItemsRepeater.Layout>
                <StackLayout Spacing="24" />
            </ItemsRepeater.Layout>

            <ItemsRepeater.ItemTemplate>
                <DataTemplate>
                    <StackPanel Spacing="8">
                        <StackPanel Name="GroupTitle" Orientation="Horizontal">
                            <TextBlock Text="{Binding Title}" FontSize="24" />
                        </StackPanel>

                        <ItemsRepeater Items="{Binding Items}">
                            <ItemsRepeater.Layout>
                                <UniformGridLayout MaximumRowsOrColumns="2"
                                                   MinColumnSpacing="12"
                                                   MinRowSpacing="12"
                                                   ItemsStretch="Fill" />
                            </ItemsRepeater.Layout>

                            <ItemsRepeater.ItemTemplate>
                                <DataTemplate>
                                    <Border Padding="12" Background="#EEEEEE">
                                        <StackPanel Spacing="6">
                                            <TextBlock Text="Item name:" />
                                            <TextBlock Text="{Binding}" />
                                        </StackPanel>
                                    </Border>
                                </DataTemplate>
                            </ItemsRepeater.ItemTemplate>
                        </ItemsRepeater>
                    </StackPanel>
                </DataTemplate>
            </ItemsRepeater.ItemTemplate>
        </ItemsRepeater>
    </ScrollViewer>

</Window>

using System.Collections.Generic;
using System.Linq;

namespace itemsrepeaterissue.ViewModels {
    public class MainWindowViewModel : ViewModelBase {
        public class ItemGroup {
            public string Title { get; }
            public IEnumerable<string> Items { get; }

            public ItemGroup(string title, IEnumerable<string> items) {
                Title = title;
                Items = items;
            }
        }

        public IEnumerable<ItemGroup> ItemGroups =>
            new[] { 20, 20, 5, 2, 2, 2 }.Select(n => {
                return new ItemGroup(
                    $"Group with {n} items",
                    Enumerable.Range(0, n).Select(i => $"Item {i}")
                );
            });
    }
}

Desktop (please complete the following information):

• OS: Windows 10 (20H2, 19042.685)
• Version 0.10.0-rc1

[grokys]

Could this be microsoft/microsoft-ui-xaml#3393 ?

Edit: actually looks like it's not as I don't think I see scrolling up in the recording.

[balthild]

Probably not. microsoft/microsoft-ui-xaml#1887 says it's specifically when using MaximumRowsOrColumns. But in the example program, after I removed the MaximumRowsOrColumns property on UniformGridLayout, the issue is still there.

In the recording, I'm not scrolling up the mouse wheel, but the ScrollViewer automatically scrolls to some positions above when it's nearly reaching the end.