new/ViewModels/MainWindowViewModel.cs

using YtYtAvalonia.Models;
using YtYtAvalonia.Views;
using YtYtAvalonia.ViewModels;
using Avalonia.Controls;
using ReactiveUI;
using YtYtAvalonia.View;
using System.Linq;

namespace YtYtAvalonia.ViewModels
{
    public class MainWindowViewModel : ViewModelBase
    {
#pragma warning disable CA1822 // Mark members as static

        public static SuharevaContext myConnection = new SuharevaContext();

        RegistrationViewModel regPage = new RegistrationViewModel(myConnection);
        public RegistrationViewModel RegPage { get => regPage; set => regPage = value; }

        public UserControl UC { get => uc; set => this.RaiseAndSetIfChanged(ref uc, value); }
        
        private UserControl uc = new LoginView();

        public void LoadRegistrationView() => UC = new RegistrationView();

        public void LoadLoginView() => UC = new LoginView();

        LoginViewModel loginVM = new LoginViewModel();

        
        public LoginViewModel LoginVM { get => loginVM; set => loginVM = value; }

        public void LoadPersonalAccount()
        {
            User? currentUser = myConnection.Users.FirstOrDefault(x => x.Login == LoginVM.Login && x.Password == LoginVM.Password);
            if(currentUser == null)
            {
                LoginVM.Message = "Пользователя с такими данными не существует.";
            }
            else
            {
                LoginVM.Message = "Ecgt[!";
                UC = new PersonalAccount();
            }
        }
    }
}