R29/WpfApp29/ViewModels/RegistrationWindowViewModel.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows;
using WpfApp29.Models;

namespace WpfApp29.ViewModels
{
    class RegistrationWindowViewModel : BaseViewModel
    {
        private User? _user;
        public User User
        {
            get { return _user ??= new User(); }
            set { _user = value; OnPropertyChanged(); }
        }
        public RelayCommand? _commandRegister;
        public RelayCommand? CommandRegister
        {
            get
            {
                return _commandRegister ??= new RelayCommand(
                x =>
                {
                    MainContext ctx = new MainContext();
                    
                    if (ctx.Users.Any(u => u.Login == User.Login))
                    {
                        MessageBox.Show("Такой логин уже занят");
                        return;
                    }

                    if (ctx.Users.Any(u => u.Phone == User.Phone))
                    {
                        MessageBox.Show("Такой номер телефона уже занят");
                        return;
                    }

                    ctx.Users.Add(User);
                    ctx.SaveChanges();
                    MainWindow mainWindow = new MainWindow();
                    MessageBox.Show(mainWindow, "Вы успешно зарегистрировались");
                    mainWindow.Show();
                    AppHelper.GetWindowAtType<RegistrationWindow>()?.Close();
                }
                );
            }
        }

        public RelayCommand? _commandGoLogin;
        public RelayCommand? CommandGoLogin
        {
            get
            {
                return _commandGoLogin ??= new RelayCommand(
                x =>
                {
                    new MainWindow().Show();
                    AppHelper.GetWindowAtType<RegistrationWindow>()?.Close();
                });
            }
        }

    }
}