KeepLastItemInView not working on iOS

[imsam67]

Description

The KeepLastItemInView doesn't seem to be working on iOS.

I have a bunch of items in a CollectionView which gets its data from an ObservableCollection in a view model. I then add a new item to ObservableCollection but the CollectionView doesn't display the newly added item. I have to manually scroll to see it.

This is happening in .NET 8 RC 2 but I observed the same behavior in .NET 7.

Here's the XAML:

...
<CollectionView
   ItemsSource={Binding FeedItems}
   ItemsUpdatingScrollMode="KeepLastItemInView">
   ...
</CollectionView>

And here's the view model:

public ObservableCollection<FeedItem> FeedItems { get; } = new();

[RelayCommand]
async Task AddItem(FeedItem newItem)
{
   FeedItems.Insert(0, newItem);
}

Steps to Reproduce

1. Add a CollectionView to a ContentPage
2. Create a corresponding ViewModel
3. Create an ObservableCollection as demonstrated above
4. Bind the CollectionView to ObservableCollection as its ItemsSource
5. Insert a new item to the ObservableCollection at index 0

Link to public reproduction project repository

No response

Version with bug

8.0.0-rc.2.9373

Is this a regression from previous behavior?

Yes, this used to work in Xamarin.Forms

Last version that worked well

Unknown/Other

Affected platforms

iOS

Affected platform versions

No response

Did you find any workaround?

Haven't found a work around yet other than Clear(); the ObservableCollection and add all the items -- including existing ones -- all over again.

Relevant log output

No response

[SamuelJames101]

Is this being looked at?

[Zhanglirong-Winnie]

Verified this issue with Visual Studio 17.10.0 Preview 1. Can repro on iOS platform.

[piersdeseilligny]

I'm having the exact same issue on macOS Catalyst, with a CollectionView inside a Grid. @imsam67 did you find a workaround?

[sorrybomber]

I can see this issue on 8.0.20. Do you know when this will be fixed?

[techking1994]

Same issue here, but after multiple trails with controls, now I am able scroll items in Collection View without going top when adding new items.
I just added Collection View in Scroll View by specifying Height of the Collection View for example HeightRequest="800" .
Observed on ios 17.4.1, on iPhone 13 PRO. with Microsoft.Maui.Controls 8.0.21
In my case :
from

<RefreshView
    x:Name="refresh"........... >
        <CollectionView
            x:Name="ItemsListView"
            ItemsUpdatingScrollMode="KeepScrollOffset"
        </CollectionView>
</RefreshView>

changed to

<RefreshView
     x:Name="refresh"........... >
<ScrollView>
         <CollectionView
             x:Name="ItemsListView"
                HeightRequest="800"
                ItemsUpdatingScrollMode="KeepScrollOffset".............
         </CollectionView>
</ScrollView>
</RefreshView> 

[piersdeseilligny]

Moving the CollectionView into a scrollview disables any caching that's going on with the CollectionView, so becomes unviable if there's more than a dozen items.

Should this not be slightly higher priority than just being in the backlog?

[lwiedemann]

For me, KeepLastItemInView for iOS did work on .NET 8 (8.0.100) but not on .NET 9 (9.0.50). Android is working for both versions.
I have a reproduction project here: .NET 8 (working) vs. .NET 9 (regressed)

My page is quite simple, ItemSource is set in the constructor and is using a ObservableCollection.

<ContentPage ...
             x:Class="Reproduction.Pages.ReproductionPage">
    <Grid RowDefinitions="*, auto, auto">
        <CollectionView Grid.Row="0" ItemsUpdatingScrollMode="KeepLastItemInView">
            <CollectionView.ItemTemplate>
                <DataTemplate>
                    <Grid RowDefinitions="auto, 60" >
                        <Label Text="{Binding .}" FontSize="Large" />
                    </Grid>
                </DataTemplate>
            </CollectionView.ItemTemplate>
        </CollectionView>
    ...
    </Grid>
</ContentPage>

public partial class ReproductionPage
{
    private ObservableCollection<string> _items = [];
    public ReproductionPage()
    {
        InitializeComponent();
        CollectionView.ItemsSource = _items;
    }

    private void OnAdd(object? sender, EventArgs e)
    {
        _items.Add($"New Item {_items.Count}");
    }
}