presence_new/Presence.Desktop/Views/PresenceView.axaml.cs

using System.Linq;
using Avalonia;
using Avalonia.Controls;
using Avalonia.Markup.Xaml;
using Avalonia.ReactiveUI;
using Presence.Desktop.Models;
using Presence.Desktop.ViewModels;
using ReactiveUI;

namespace Presence.Desktop.Views;

public partial class PresenceView : ReactiveUserControl<PresenceViewModel>
{
    public PresenceView()
    {
        this.WhenActivated(disposables => { });
        AvaloniaXamlLoader.Load(this);    }
    
    private void OnDataGridSelectionChanged(object sender, SelectionChangedEventArgs e)
    {
        if (this.DataContext is PresenceViewModel viewModel)
        {
            // Обновляем выделенные элементы в ViewModel
            viewModel.SelectedItems.Clear();
            foreach (var item in e.AddedItems.OfType<PresencePresenter>())
            {
                viewModel.SelectedItems.Add(item);
            }
        }
    }
}