Windows File Extension Association Helper Class

FileAssociation.cs

using System;
using System.Reflection;
using System.Runtime.InteropServices;
using Microsoft.Win32;

namespace DiskCatalog.Classes
{
    public sealed class FileAssociation
    {
        public string Extension { get; }
        public string ProgId { get; }
        public string Description { get; }
        private readonly string _execPath = Assembly.GetExecutingAssembly().Location;
        private readonly Scope _scope;

        public FileAssociation(string extension, string progId, string description, Scope scope)
        {
            Extension = extension;
            ProgId = progId;
            Description = description;
            _scope = scope;
        }

        public void EnsureSet(bool editContext, bool resetExplorerOverride)
        {
            var changeNotify = false;
            RegistryKey classesKey = _scope == Scope.Root
                ? Registry.ClassesRoot
                : Registry.CurrentUser.OpenSubKey(@"SOFTWARE\Classes", true);
            if (classesKey == null)
                throw new NullReferenceException();
            try
            {
                using (RegistryKey extensionKey = classesKey.CreateSubKey(Extension))
                {
                    if (extensionKey == null)
                        throw new NullReferenceException();
                    extensionKey.SetValue(null, ProgId);
                }

                using (RegistryKey progIdKey = classesKey.CreateSubKey(ProgId,
                    RegistryKeyPermissionCheck.ReadWriteSubTree))
                {
                    if (progIdKey == null)
                        throw new NullReferenceException();
                    progIdKey.SetValue(null, Description);
                    using (RegistryKey keyIcon = progIdKey.CreateSubKey("DefaultIcon"))
                    {
                        if (keyIcon == null)
                            throw new NullReferenceException();
                        keyIcon.SetValue(null, $"\"{_execPath}\",0");
                    }
                    using (RegistryKey shellKey = progIdKey.CreateSubKey("Shell"))
                    {
                        if (shellKey == null)
                            throw new NullReferenceException();
                        if (SetShellCommand(shellKey, "open"))
                            changeNotify = true;
                        if (editContext)
                        {
                            if (SetShellCommand(shellKey, "edit"))
                                changeNotify = true;
                        }
                        else
                        {
                            try
                            {
                                shellKey.DeleteSubKeyTree("edit", true);
                                changeNotify = true;
                            }
                            catch (ArgumentException)
                            {
                            }
                        }
                    }
                }
            }
            finally
            {
                classesKey.Dispose();
            }

            if (resetExplorerOverride && ResetExplorerOverride())
                changeNotify = true;

            if (changeNotify)
                NativeMethods.SHChangeNotify(SHCNE_ASSOCCHANGED, SHCNF_FLUSH, IntPtr.Zero, IntPtr.Zero);
        }

        public void UnSet(bool resetExplorerOverride)
        {
            var changeNotify = false;
            RegistryKey classesKey = _scope == Scope.Root
                ? Registry.ClassesRoot
                : Registry.CurrentUser.OpenSubKey(@"SOFTWARE\Classes", true);
            if (classesKey == null)
                throw new NullReferenceException();
            try
            {
                try
                {
                    classesKey.DeleteSubKey(Extension, true);
                    changeNotify = true;
                }
                catch (ArgumentException)
                {
                }

                try
                {
                    classesKey.DeleteSubKeyTree(ProgId, true);
                    changeNotify = true;
                }
                catch (ArgumentException)
                {
                }
            }
            finally
            {
                classesKey.Dispose();
            }

            if (resetExplorerOverride && ResetExplorerOverride())
                changeNotify = true;

            if (changeNotify)
                NativeMethods.SHChangeNotify(SHCNE_ASSOCCHANGED, SHCNF_FLUSH, IntPtr.Zero, IntPtr.Zero);
        }

        private bool SetShellCommand(RegistryKey shellKey, string cmdKeyName)
        {
            var changeNotify = false;
            using (RegistryKey cmdKey = shellKey.CreateSubKey(cmdKeyName))
            {
                if (cmdKey == null)
                    throw new NullReferenceException();

                using (RegistryKey commandKey = cmdKey.OpenSubKey("command"))
                    if (commandKey == null)
                        changeNotify = true;
                using (RegistryKey commandKey = cmdKey.CreateSubKey("command"))
                {
                    if (commandKey == null)
                        throw new NullReferenceException();
                    commandKey.SetValue(null, $"\"{_execPath}\" \"%1\"");
                }
            }
            return changeNotify;
        }

        private bool ResetExplorerOverride()
        {
            string keyPath = $@"Software\Microsoft\Windows\CurrentVersion\Explorer\FileExts\{Extension}";
            using (RegistryKey currentUser = Registry.CurrentUser)
            using (RegistryKey explorerOverride = currentUser.OpenSubKey(keyPath, true))
            {
                if (explorerOverride != null)
                {
                    try
                    {
                        explorerOverride.DeleteSubKey("UserChoice", true);
                        return true;
                    }
                    catch (ArgumentException)
                    {
                    }
                }
            }
            return false;
        }

        public enum Scope
        {
            CurrentUser,
            Root
        }

        private const int SHCNE_ASSOCCHANGED = 0x8000000;
        private const int SHCNF_FLUSH = 0x1000;

        private static class NativeMethods
        {
            [DllImport("shell32", CharSet = CharSet.Auto, SetLastError = true)]
            public static extern void SHChangeNotify(uint wEventId, uint uFlags, IntPtr dwItem1, IntPtr dwItem2);
        }
    }
}