Simple app settings class

AppSettings.cs

using System;
using System.Collections;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Runtime.Serialization;
using System.Runtime.Serialization.Formatters.Binary;
using System.Windows;
using System.Windows.Media;
using FirstFloor.ModernUI.Presentation;

namespace MegaTestBuilder
{
	internal static class AppSettings
	{
		[Serializable]
		internal sealed class AppSettingsData : ISerializable
		{
			public Rect? MainWindowLocation { get; set; }

			public string LastConnectionString { get; set; }

			public string LastGeneratedTestSetDirectory { get; set; }

			public string LastRawDataDirectory { get; set; }

			public string LastTemplateDirectory { get; set; }

			public bool? LastBuildProject { get; set; }

			public string LastNamespace { get; set; }

			public string LastQuery { get; set; }

			public string LastOutputDirectory { get; set; }

			public string AccentColor { get; set; }

			public FontSize? FontSize { get; set; }

			public Uri ThemeSource { get; set; }

			public AppSettingsData()
			{				
			}

			private static IEnumerable<TItem> ToEnumerable<TItem>(IEnumerator source)
			{
				while (source.MoveNext())
				{
					yield return (TItem) source.Current;
				}
			}

			private AppSettingsData(SerializationInfo info, StreamingContext context)
			{
				var items = ToEnumerable<SerializationEntry>(info.GetEnumerator())
					.ToDictionary(k => k.Name, v => v.Value);

				foreach (var prop in typeof (AppSettingsData).GetProperties())
				{
					object value;
					if (items.TryGetValue(prop.Name, out value))
					{
						prop.SetValue(this, value);
					}
				}
			}

			public void GetObjectData(SerializationInfo info, StreamingContext context)
			{
				foreach (var prop in typeof(AppSettingsData).GetProperties())
				{
					info.AddValue(prop.Name, prop.GetValue(this), prop.PropertyType);
				}
			}
		}

		private static AppSettingsData _instance;
		private static readonly object _guard = new object();

		public static AppSettingsData Instance
		{
			get
			{
				if (_instance == null)
				{
					Initialize();
				}

				return _instance;
			}
		}

		private const string SettingsFileName = ".MegaTestBuilder.AppSettings";

		enum SaveState
		{
			Save,
			Defer,
			Abandon
		}

		private static SaveState _state;

		struct SaveDeferer : IDisposable
		{
			public void Dispose()
			{
				if (_state == SaveState.Defer)
				{
					_state = SaveState.Save;
					Save();
				}
			}
		}

		public static IDisposable DeferSave()
		{
			_state = SaveState.Defer;
			return new SaveDeferer();
		}

		public static void AbandonSave()
		{
			_state = SaveState.Abandon;
		}

		public static void Save()
		{
			if (_instance == null ||
				_state != SaveState.Save)
			{
				return;
			}

			lock (_guard)
			{
				var instance = _instance;

				var path = Path.Combine(Environment.GetFolderPath(Environment.SpecialFolder.LocalApplicationData),
					SettingsFileName);

				using (var output = File.OpenWrite(path))
				{
					var serializer = new BinaryFormatter();
					serializer.Serialize(output, instance);
				}
			}
		}

		private static void Initialize()
		{
			if (_instance == null)
			{
				lock (_guard)
				{
					if (_instance != null)
					{
						return;
					}

					var path = Path.Combine(Environment.GetFolderPath(Environment.SpecialFolder.LocalApplicationData),
						SettingsFileName);
					if (File.Exists(path))
					{
						try
						{
							using (var settings = File.OpenRead(path))
							{
								var serializer = new BinaryFormatter();
								_instance = serializer.Deserialize(settings) as AppSettingsData;
							}
							return;
						}
						catch (Exception)
						{
							File.Delete(path);
							//ignore errors - start with clean settings
						}
					}
					_instance = new AppSettingsData();
				}
			}
		}
	}
}