ListBox selection doesn't update when items are added or removed.

[Shadowblitz16]

Describe the bug

I have this code here...

public partial class Layers : BaseViewModel
{
    [ObservableProperty]
    [NotifyPropertyChangedFor(nameof(SelectedName))]
    private IList<Layer> _items = new ObservableCollection<Layer>() {
        Layer.Default
    };

    [ObservableProperty]
    [NotifyPropertyChangedFor(nameof(SelectedName))]
    private IList<Layer> _selectedItems = new ObservableCollection<Layer>()
    {
        Layer.Default
    };

    [ObservableProperty]
    [NotifyPropertyChangedFor(nameof(SelectedName))]
    private Layer? _selectedItem = Layer.Default;
    
    [ObservableProperty]
    [NotifyPropertyChangedFor(nameof(SelectedName))]
    private int _selectedIndex = 0;

    public string SelectedName
    {
        get => SelectedItem?.Name ?? string.Empty;
        set
        {
            if (SelectedName != value)
            {
                foreach (var item in SelectedItems)
                {
                    item.Name = value;
                }
            }
        }
    }

    [RelayCommand]
    private void InsertItem()
    {
        Items.Insert(SelectedIndex+1, new Layer());
    }

    [RelayCommand]
    private void RemoveItems()
    {
        foreach (var item in SelectedItems.ToList())
        {
            if (item.IsReadonly) continue;
            Items.Remove(item);
        }
           
    }
}

and this axaml here...

<UserControl xmlns="https://github.com/avaloniaui"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
             xmlns:vm="clr-namespace:Quest.ViewModels.Controls"
             xmlns:v="clr-namespace:Quest.Views.Controls"
             mc:Ignorable="d" d:DesignWidth="800" d:DesignHeight="450"
             x:Class="Quest.Views.Controls.LayersView"
             x:DataType="vm:Layers">
    
    <Design.DataContext>
        <!-- This only sets the DataContext for the previewer in an IDE,
             to set the actual DataContext for runtime, set the DataContext property in code (look at App.axaml.cs) -->
        <vm:Layers/>
    </Design.DataContext>
    
    <Grid RowDefinitions="*, Auto" Margin="3" RowSpacing="3">
        <ListBox Grid.Row="0" SelectionMode="Multiple, AlwaysSelected" ItemsSource="{Binding Items}" SelectedItems="{Binding SelectedItems}" SelectedItem="{Binding SelectedItem}" SelectedIndex="{Binding SelectedIndex}">
            <ListBox.ItemTemplate>
                <DataTemplate>
                    <v:LayerView />
                </DataTemplate>
            </ListBox.ItemTemplate>
        </ListBox>
        <Grid Grid.Row="1" ColumnDefinitions="Auto, Auto, *" ColumnSpacing="3">
            <Button Grid.Column="0" MinWidth="24" Command="{Binding InsertItemCommand}">+</Button>
            <Button Grid.Column="1" MinWidth="24" Command="{Binding RemoveItemsCommand}">-</Button>
            <TextBox Grid.Column="2" Text="{Binding SelectedName}"/>
        </Grid>
    </Grid>
</UserControl>

when I click the + button it should find the last selected item index in the items source and select it.
when I click the - button it should select the item before the first item in the selection.

To Reproduce

• Post code and axaml in a avalonia project.
• Compile
• If you are using rider click on the + and - buttons and see that selection doesn't work properly

Expected behavior

SelectedItems, SelectedItem and SelectedIndex should all update.

Avalonia version

11.3.2

OS

Linux

Additional context

I have been fighting with this for 2 days.
I can't figure out how to get it to work in all cases.

It should work regardless of what selection mode we use.

[timunie]

Please use Discussions for questions or join us on Telegram. Thank you

[timunie]

I don't see where you even select a new item in code. Also use only one way to select an item, not all 3.possible ways. This will conflict with each other.

[Shadowblitz16]

@timunie is there documentation on how to do multi/always selection?

I didn't see any.

I assumed listbox handled selection automatically when we add and remove items to it.
because it should.

Handling it manually is a big pain.

[timunie]

No Listbox should never select anything on its own. It's up to the user or up to you. Just setting selectedItem or SelectedIndex in your VM should be enough.