Microsoft.Win32.Registry的GetValue不使用默认值

Question

I have a legacy (I didn't build it) application running on an x64 environment (Win7). I have a sneaking suspicion it was run on a 32-bit environment before.

Anyway, I see calls to Registry.GetValue(key, value, default) .

It seems like the default value is ignored.

Check out this crazy code:

// Up above the sky, so high
using Microsoft.Win32;
// ...
string location = "HKEY_LOCAL_MACHINE\SOFTWARE\..."; // ...
// ...

string registryValue = (string)Registry.GetValue(location, "Uri", "http://localhost/");
if (string.isNullOrEmpty(registryValue) {
  throw new Exception("What the ... ?!");
}

In a comparable example, the exception is seriously being thrown. (Actually, a null-reference exception appears despite the default value).

And I checked that I have the registry keys all the way up to the last level; they're all in my registry.

This works for someone , but not for me.

Is this a bug? What's going on here?

Answer 1

Most likely you are being caught out by registry redirection . You have a 32 bit process running on a 64 bit system. So HKLM\\Software is redirected to HKLM\\Software\\Wow6432Node .

When the key does not exist, the Registry.GetValue returns null rather than the default value and so the exception is thrown.

If the name is not found in the specified key, returns a default value that you provide, or null if the specified key does not exist.

Answer 2

The default value is only returned if the specified key (that is the first parameter, ie location in your example) is found but a value with the specified name (the second parameter, "Uri" in your example) does not exist within that key.

If the key itself does not exist a null reference is returned.

This is fairly well documented on MSDN .

Probably the key you are looking for does not exist, probably because you are running on a 64-bit environment now which means that in case your application is a 32-bit process the HKLM\\Software key gets mapped to HKLM\\Software\\Wow6432Node .

Answer 3

I've no idea why but i solved using

My.Computer.Registry.CurrentUser.GetValue("Software\Mykey","Default Value")
instead of
My.Computer.Registry.GetValue("HKEY_CURRENT_USER\Software","Mykey","Default Value")

If the key doesn't exist the first example returns "Default Value", the second a null object!

Answer 4

I know this is ancient, but in case anybody else stumbles upon this issue, I found an approach that works well for me. I'm using OpenSubKey, instead of GetValue.

RegistryKey key = Registry.CurrentUser.OpenSubKey(@"Software\MyProduct");
string data = key.GetValue("MyValue") as string;

The registry's terminology caused me some confusion. It is not simply a key -> value store, it is more like key -> value -> data.