Create a REG_NONE empty value in the Windows Registry via C#

Question

How can I create an empty value in the Windows Registry that has the type REG_NONE?

For instance, for this key:

HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\FileExts\
  .htm\OpenWithProgids

Here are the values that I see on my Windows 7 machine:

----------------------------------------------------
Name           Type       Data
----------------------------------------------------
(Default)      REG_SZ     (value not set)
FirefoxHTML    REG_NONE   (zero-length binary value)
htmlfile       REG_NONE   (zero-length binary value)
----------------------------------------------------

Specifically, how do I declare and initialize a variable of type "zero-length binary value" for the purpose of passing it to RegistryKey.SetValue? Note that I could not find the help that I needed in the documentation for the RegistryValueKind enumeration.

Tattletale

Answer 1

[Here is the result of my research.]

I found the hint I was looking for in Microsoft's reference source for RegistryKey.cs:

byte[] value = new byte[0];

Specifically, call RegistryKey.SetValue where:

• name is set to the name you want for the key,
• value is set to an empty byte array, and
• valueKind is set to RegistryValueKind.None.

 using Microsoft.Win32;

 RegistryKey key; // set via 'CreateSubKey' or 'OpenSubKey'
 key.SetValue("KeyName", new byte[0], RegistryValueKind.None);

However, note that at least for values that appear in an OpenWithProgids key, Windows also appears to treat empty string values as equivalent:

 key.SetValue("KeyName", string.Empty, RegistryValueKind.String);

For instance, for this key:

HKEY_CLASSES_ROOT\.vcxproj\OpenWithProgids

Here are the values that I see on my machine:

---------------------------------------------------------------
Name                                  Type      Data
---------------------------------------------------------------
(Default)                             REG_SZ    (value not set)
Expression.Blend.vcsproj.12.0         REG_SZ
VisualStudio.Launcher.vcxproj.10.0    REG_SZ
VisualStudio.Launcher.vcxproj.12.0    REG_SZ
VisualStudio.vcxproj.10.0             REG_SZ
VisualStudio.vcxproj.12.0             REG_SZ
---------------------------------------------------------------

Related: See this answer and this answer for examples for how to set the data of a Registry value of type RegistryValueKind.Binary to a non-empty byte array.

Tattletale