Programmatically setting the SelectedItem of a CollectionView is not working on iOS

Question

I am populating a screen with a CollectionView and I'd like to preselect the SelectedItem. On Android (left screenshot), this works fine, but not on iOS (right screenshot) - only manual selection by the user seems to change the UI.

To reproduce, use the standard MAUI template app, replace the XAML of the MainPage with

<?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="MyMAUIApp.MainPage">
    <CollectionView ItemSizingStrategy="MeasureAllItems" BackgroundColor="Yellow"
                            ItemsSource="{Binding Items}"
                            SelectedItem="{Binding SelectedItem, Mode=TwoWay}"
                            SelectionMode="Single">
        <CollectionView.ItemsLayout>
            <GridItemsLayout Orientation="Vertical" Span="2"/>
        </CollectionView.ItemsLayout>
        <CollectionView.ItemTemplate>
            <DataTemplate>
                <Grid HeightRequest="50" WidthRequest="50">
                    <VisualStateManager.VisualStateGroups>
                        <VisualStateGroup x:Name="CommonStates">
                            <VisualState x:Name="Normal"/>
                            <VisualState x:Name="Selected">
                                <VisualState.Setters>
                                    <Setter Property="BackgroundColor" Value="Red"/>
                                </VisualState.Setters>
                            </VisualState>
                        </VisualStateGroup>
                    </VisualStateManager.VisualStateGroups>
                    <Label Text="Text" />
                </Grid>
            </DataTemplate>
        </CollectionView.ItemTemplate>
    </CollectionView>
</ContentPage>

and the C# with

using System.Collections.ObjectModel;

namespace MyMAUIApp;

public partial class MainPage : ContentPage {
    public MainPage() {
        InitializeComponent();
        BindingContext = this;

        SelectedItem = Items[0];
        OnPropertyChanged(nameof(SelectedItem));
    }

    public ObservableCollection<string> Items { get; } = new ObservableCollection<string>(new List<string> {
        "A", "B", "C", "D"
    });

    public string SelectedItem { get; set; }
}

Is this a MAUI bug? Can I avoid it somehow? In the situation where I encounter this, I have some degree of success with refreshing the Items after a short delay and/or subsequently invoking OnPropertyChanged(nameof(Items)) but not always.

Moving the code to OnAppearing(), as suggested in the comments, doesn't work:

protected override void OnAppearing() {
    base.OnAppearing();
    SelectedItem = Items[0];
    OnPropertyChanged(nameof(SelectedItem));
}

An example of how to make it work, but in a really awkward way:

public MainPage() {
    InitializeComponent();
    BindingContext = this;

    _ = Task.Run(async () => {
        await Task.Delay(100);
        Dispatcher.Dispatch(() => {
            SelectedItem = Items[0];
            OnPropertyChanged(nameof(SelectedItem));
        });
    });
}

Answer 1

Yes, it is a potential issue on iOS. For now, setting the SelectedItem property from ViewModel is not working on iOS. And it is a known issue that is being tracked in the links below, you can follow up there.

https://github.com/dotnet/maui/issues/13059

https://github.com/dotnet/maui/issues/13072

As a workaround(awkaward however useful) suggested by Glorfindel like below:

    _ = Task.Run(async () => {
        await Task.Delay(100);
        Dispatcher.Dispatch(() => {
            SelectedStates = new ObservableCollection<object>(ss);
            OnPropertyChanged(nameof(SelectedStates));
        });
    });