ModernWpfPlayground/App/MvvmStuff/BaseViewModel.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Runtime.CompilerServices;
using FastMember;
using Prism.Mvvm;

namespace ModernWpfPlayground.MvvmStuff
{
    public abstract class BaseViewModel : BindableBase
    {
        protected BaseViewModel()
        {
            ObjectAccessor = ObjectAccessor.Create(this);
        }

        private readonly Dictionary<string, object?> _values = new Dictionary<string, object?>();
        protected readonly ObjectAccessor ObjectAccessor;

        protected IReadOnlyDictionary<string, object?> Values => _values;

        protected bool SetProperty<T>(T value, Action<T>? onChanged = null,
            [CallerMemberName] string? propertyName = null)
        {
            if (propertyName == null) throw new ArgumentNullException(nameof(propertyName));
            if (_values.TryGetValue(propertyName, out var obj) && Equals(value, obj)) return false;

            _values[propertyName] = value;
            RaisePropertyChanged(propertyName);
            onChanged?.Invoke(value);
            return true;
        }

        protected T GetProperty<T>(T defaultValue = default, [CallerMemberName] string? propertyName = null)
        {
            if (propertyName == null) throw new ArgumentNullException(nameof(propertyName));
            return Values.TryGetValue(propertyName, out var obj) ? (T)obj! : defaultValue;
        }

        protected void ResetViewModel(Func<string, bool>? predicate = null)
        {
            IEnumerable<string> keys = _values.Keys.ToArray();
            if (predicate != null) keys = keys.Where(predicate);
            foreach (var key in keys)
            {
                var currentValue = ObjectAccessor[key];
                _values.Remove(key);
                var newValue = ObjectAccessor[key];
                if (Equals(currentValue, newValue)) continue;
                _values.Add(key, currentValue);
                ObjectAccessor[key] = newValue;
            }
        }

        protected abstract IEnumerable<(string key, object? value)> GetViewModelItems();

        protected void LoadViewModel()
        {
            var keysFromFile = new SortedSet<string>();
            foreach (var (key, value) in GetViewModelItems())
            {
                keysFromFile.Add(key);
                ObjectAccessor[key] = value;
            }

            ResetViewModel(x => !keysFromFile.Contains(x));
        }
    }
}