WiX RegistryValue setting to null (Value="") - wix

Question

I've been working on a WiX project for some time, and consuming the registry values that my setup initializes has proven to be "interesting". I am looking for a sanity check here, please.
I have the following line in my WiX script that creates a registry value:
<RegistryValue Type="multiString" Name="polling_manifest" Value="" />
This creates a registry value with the data that looks like this (from regedit/export):
"polling_manifest"=hex(7):00,00,00,00
which, to me, looks like a string[2] with two null strings in it. In actuality, if you open this registry value with something like:
public static string[] pollingManifestValue
{
get
{
return (string[])RegistryKey.OpenBaseKey(RegistryHive.LocalMachine, RegistryView.Registry64)
.OpenSubKey(AppSettingsGet("RegPathKeyConary"))
.GetValue(AppSettingsGet("rTISRegKeyPollingManifest"));
}
set
{
RegistryKey.OpenBaseKey(RegistryHive.LocalMachine, RegistryView.Registry64)
.OpenSubKey(AppSettingsGet("RegPathKeyConary"), true)
.SetValue(AppSettingsGet("rTISRegKeyPollingManifest"), value);
}
}
pollingManifestValue comes back as null. Consequently, all my code that accesses this construct has to have the "check for null first, then access properties"-type code.
I understand that those checks are the right thing to do, and I am not looking to be a more lazy programmer here. I am looking for thoughts and suggestions of those more experienced than I with the WiX deep magic, because it feels to me like I am not doing it optimally. Any code review / usage guidance is most welcome, and I thank you in advance.

Answer 1

Internally, REG_MULTI_SZ (Type="multiString") values are represented by a sequence of null-terminated strings, terminated by an empty string.
While this MSDN page clearly states that it is not possible to include a zero-length string in the sequence, tools like WiX do allow for writing empty strings to the registry. Registry Editor, while displaying such values properly in some places, will remove empty strings before saving.
So your example
<RegistryValue Type="multiString" Name="polling_manifest" Value="" />
which can also be written as follows to make its intention more clear
<RegistryValue Type="multiString" Name="polling_manifest">
<MultiStringValue></MultiStringValue>
</RegistryValue>
will be written to the registry as an empty string, followed by a \0 character, followed by the sequence-terminating \0 character. With each character represented by two bytes, the entire sequence is exported as "polling_manifest"=hex(7):00,00,00,00.
While testing this, I found that .NET, at least in version 4, doesn't use c-style string processing for reading REG_MULTI_SZ values, and can clearly process empty strings. Using code like yours clearly returned a string array containing one empty string element.
I noticed you're using the 64-bit registry view in your code, however it is unclear whether your value will be written to this registry view. Furthermore key path and value name are read from configuration; are you sure they are correct?

Answer 2

Create registry entry using this code
<RegistryKey Id="ServiceName" Action="createAndRemoveOnUninstall" Key="SOFTWARE\ProductName\[ProductCode]\FeatureName" Root="HKLM">
<RegistryValue Id="ServiceName" Type="string" Name="ABC" Value="[SERVICENAME]"></RegistryValue>
<RegistryValue Id="ServiceInstallLocation" Type="string" Name="ServiceInstallLocation" Value="[INSTALLLOCATION2]"></RegistryValue>
</RegistryKey>
For reading registry you can use the straight forward code like below
string processor = System.Environment.GetEnvironmentVariable("PROCESSOR_ARCHITECTURE");
processor = processor.Substring(processor.Length - 2, 2);
if (processor == "86")
{
regkey = Registry.LocalMachine.OpenSubKey("Software\\ABC company");
}
else
{
regkey = Registry.LocalMachine.OpenSubKey("Software\\Wow6432Node\\ABC company");
}
Then fetch the values
Registry.GetValue(regkey + "\\Services", "ServiceName", "0")
If it returns "0" then value does not exists else it will give you the service name.