How do I read the registry in 32-bit c# app such that registry redirection works on 64-bit Windows 7

Question

My boss just got Windows 7 and he tried running one of our installers which runs perfectly fine under XP. On Windows 7, the installer runs without giving any errors. However, it does not create registry keys under HKEY_LOCAL_MACHINE\SOFTWARE{Company}{product}. These keys get created correctly under XP.

Has anyone encountered this issue? I suspect it is a rights/security issue but I'm not sure and I don't have Windows 7 to experiment with.

EDIT

The computer in question is a 64-bit machine running 64-bit Windows. It turns out Windows 7 redirects 32-bit applications to HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node{Company}{product}. The problem is my application code tries to access the registry using a hardcoded value like this:

var t = Registry.GetValue("HKEY_LOCAL_MACHINE\\SOFTWARE\\..., "ValueName", DefaultValue);

So, my new question is how do I access the registry such that the Windows 9 registry redirection will just work?

Answer 1

If you're using .NET 4, you can specifically request that your 32-bit (or 64-bit) process access the 64-bit view of the registry using the RegistryKey.OpenBaseKey method.

Cf. http://msdn.microsoft.com/en-us/library/microsoft.win32.registrykey.openbasekey.aspx

Here's an example that reads a value from the 64-bit view of the registry, even if it runs as part of a 32-bit process:

var hklm64 = RegistryKey.OpenBaseKey(RegistryHive.LocalMachine, RegistryView.Registry64);
var key = hklm.OpenSubKey(@"SOFTWARE\AcmeSoft\AnvilMaker 1.0");
var value = (string) key.GetValue("Blacksmith Name");

The RegistryKey.OpenBaseKey method also allows you to explicitly open a 32-bit view of the registry. This is useful if you're trying to go the other way around and access the 32-bit view of the registry from a 64-bit process and you don't want to explicitly add "Wow6432Node" to the registry path.

For example, today I needed to delete a sub-key tree in both the 32-bit and 64-bit views of the registry. Doing this in .NET 4 with a single registry path was easy:

foreach(var view in new[] {RegistryView.Registry32, RegistryView.Registry64})
{
     var hklm = RegistryKey.OpenBaseKey(RegistryHive.LocalMachine, view);
     hklm.DeleteSubKeyTree(@"SOFTWARE\AcmeSoft\SomeKeyWeNoLongerWant", throwOnMissingSubKey: false);
}   

On a 64-bit version of windows, the above code will remove the following sub-key trees from the registry:

Computer\HKEY_LOCAL_MACHINE\SOFTWARE\AcmeSoft\SomeKeyWeNoLongerWant
Computer\HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\AcmeSoft\SomeKeyWeNoLongerWant

-Adam

Answer 2

After more digging I came across this link which describes the registry access rules for .NET applications. My program had initially been targeted for "AnyCpu" which causes the app to target the 64-bit registry even though Windows installed it under the Wow6432Node. By setting the target to "x86" my program "magically" started accessing the registry under the Wow6432Node. Go figure!