1314/prakt1314/ViewModels/MainWindowViewModel.cs

using Avalonia.Controls;
using ReactiveUI;
using System.Linq;

namespace prakt1314.ViewModels
{
    public class MainWindowViewModel : ViewModelBase
    {
        public MainWindowViewModel() 
        {
            AuthPageViewModel apvm = new AuthPageViewModel();
            apvm.NotifyUserWasSuccessfulAuthorize += NotifyUserWasSuccessfulAuthorize;
            UserControl = (new ViewLocator()).Build(apvm);
        }

        private void NotifyUserWasSuccessfulAuthorize(int userID)
        {
            _userID = userID;
            UserRole role;
            using (AvaloniaPrakt13DbContext _dbContextForThis = new AvaloniaPrakt13DbContext()) role = _dbContextForThis.UserRoles.Where(a => (a.UserLogins.Where(a => a.IdUser == userID)).LongCount() == 1).First();
            switch (role.IdRole)
            {
                case 1:
                    {
                        CourcesListViewModel CLVM = new CourcesListViewModel();
                        UserControl = (new ViewLocator()).Build(CLVM);
                        break;
                    }
                case 2:
                    {
                        CabinetViewModel CVM = new CabinetViewModel(_userID);
                        UserControl = (new ViewLocator()).Build(CVM);
                        return;
                    }
                default:
                    {
                        return;
                    }
            }
        }

        public Control UserControl
        {
            get => _userControl;
            set => this.RaiseAndSetIfChanged(ref _userControl, value);
        }


        private Control _userControl;

        private int _userID;
    }
}