source: Common/Registry.cs

using Microsoft.Win32;

namespace Common
{
    public static class RegistryExtension
    {
        public static bool GetValueBool(this RegistryKey regKey, string name, bool defaultValue)
        {
            object value = regKey.GetValue(name, defaultValue);
            if (value is string)
            {
                if ((string)value == "True") return true;
                else return false;
            }
            else return defaultValue;
        }

        public static bool? GetValueBoolNullable(this RegistryKey regKey, string name, bool? defaultValue)
        {
            object value = regKey.GetValue(name, defaultValue);
            if (value is string)
            {
                if ((string)value == "False") return false;
                else if ((string)value == "True") return true;
                else return null;
            }
            else return defaultValue;
        }

        public static string GetValueString(this RegistryKey regKey, string name, string defaultValue)
        {
            object value = regKey.GetValue(name, defaultValue);
            if (value is string) return (string)value;
            else return defaultValue;
        }

        public static int GetValueInt(this RegistryKey regKey, string name, int defaultValue)
        {
            object value = regKey.GetValue(name, defaultValue);
            if (value is int) return (int)value;
            else return defaultValue;
        }

        public static int? GetValueIntNullable(this RegistryKey regKey, string name, int? defaultValue)
        {
            object value = regKey.GetValue(name, defaultValue);
            if (value is int) return (int)value;
            else if (value is string && (string)value == "") return null;
            else return defaultValue;
        }

        public static long GetValueLong(this RegistryKey regKey, string name, long defaultValue)
        {
            object value = regKey.GetValue(name, defaultValue);
            if (value is string && long.TryParse(value.ToString(), out long longValue)) return longValue;
            else return defaultValue;
        }

        public static float GetValueFloat(this RegistryKey regKey, string name, float defaultValue)
        {
            object value = regKey.GetValue(name, defaultValue.ToString());
            if (float.TryParse((string) value, out float num))
            {
                return num;
            }
            else return defaultValue;
        }

        public static double GetValueDouble(this RegistryKey regKey, string name, double defaultValue)
        {
            object value = regKey.GetValue(name, defaultValue.ToString());
            if (double.TryParse((string)value, out double num))
            {
                return num;
            }
            else return defaultValue;
        }

        public static double? GetValueDoubleNullable(this RegistryKey regKey, string name, double? defaultValue)
        {
            object value = regKey.GetValue(name, defaultValue.ToString());
            if (double.TryParse((string)value, out double num))
            {
                return num;
            }
            else if (value is string && (string)value == "") return null;
            else return defaultValue;
        }

        public static void SetValueBool(this RegistryKey regKey, string name, bool value)
        {
            if (value) regKey.SetValue(name, "True");
                else regKey.SetValue(name, "False");
        }

        public static void SetValueBoolNullable(this RegistryKey regKey, string name, bool? value)
        {
            if (value != null)
            {
                if (value.Value) regKey.SetValue(name, "True");
                else regKey.SetValue(name, "False");
            } else regKey.SetValue(name, "");
        }
    
        public static void SetValueString(this RegistryKey regKey, string name, string value)
        {
            if (value == null) value = "";
            regKey.SetValue(name, value);
        }

        public static void SetValueInt(this RegistryKey regKey, string name, int value)
        {
            regKey.SetValue(name, value);
        }

        public static void SetValueIntNullable(this RegistryKey regKey, string name, int? value)
        {
            if (value != null)
            {
                regKey.SetValue(name, value.Value);
            } else regKey.SetValue(name, "");
        }

        public static void SetValueLong(this RegistryKey regKey, string name, long value)
        {
            regKey.SetValue(name, value);
        }

        public static void SetValueFloat(this RegistryKey regKey, string name, float value)
        {
            regKey.SetValue(name, value);
        }

        public static void SetValueDouble(this RegistryKey regKey, string name, double value)
        {
            regKey.SetValue(name, value);
        }

        public static void SetValueDoubleNullable(this RegistryKey regKey, string name, double? value)
        {
            if (value != null)
            {
                regKey.SetValue(name, value);
            }
            else regKey.SetValue(name, "");
        }
    }
}