MyDiplom/ViewModels/UserViewModels.cs

using MyDiplom.Models;

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

using Windows.System;

namespace MyDiplom.ViewModels
{
    public class UserViewModels : BaseViewModel
    {
        public ApplicationUser User { get; set; } = new ApplicationUser();
        public UserViewModels()
        {
            User = new ApplicationUser { DisplayName = "Вася" };
            LoadUserData();
        }

        public void UpdateBalance(decimal amount)
        {
            if (amount != 0)
            {
                User.Balance += amount;
                OnPropertyChanged(nameof(User));
                SaveUserData();

            }
        }
        private void SaveUserData()
        {
            Preferences.Set("UserBalance", User.Balance.ToString());
            Preferences.Set("UserDisplayName", User.DisplayName);
        }

        private void LoadUserData()
        {
            
            string balanceString = Preferences.Get("UserBalance", "0");
            User.Balance = decimal.TryParse(balanceString, out var balance) ? balance : 0;

            User.DisplayName = Preferences.Get("UserDisplayName", "Вася"); 
        }

    }
}