In that case you'll have to do a little more work. You can get the list if
installed Framework Versions from this registry key:

HKEY_LOCAL_MACHINE,"Software\Microsoft\ASP.Net

It will look like so:

ASP.NET
--1.1.4322.0
--2.0.50727.0
--MachineAccounts

You can then enumerate through the subkeys, which are the.NET framework
versions, until you get the one you are interested in. (Sans the last one!)

You can then extract the .NET framework location using the PATH key

Caveat: This will only work if asp.net is installed on the machine, but
since you know this to be the case this shouldn't be too much of a problem

Hi Chuck,

I agree with you that the following statement will return the path of the
CLR that currently runs the assembly, which maybe not the latest version of
CLR installed on the machine:

string location
=System.Runtime.InteropServices.RuntimeEnvironment.GetRuntimeDirectory();

NET Framework with different versions can be installed side by side on a
machine. When a .NET program runs, it will use the same version of CLR it
is built on, only if this version of CLR has been installed. So it's not
possible to detect the latest version of CLR in a .NET program using any
existing .NET class related to the CLR.

So we must do it by other means.

When we install .NET Framework on a machine, some information is recorded
in the registry. Type "regedit" in the run prompt to open registry editor.
Navigate to HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\.NETFramework. You will
see an item named "InstallRoot", which records a general path of CLR. The
value of this item on my machine is "C:\WINNT\Microsoft.NET\Framework".

Unfortunately, there is not a value in the registry that contains the path
of the latest version of CLR. But all versions of installed CLR are listed
under the "HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\.NETFramework\" branch as
sub keys, such as v2.0.50727 and v3.0. Thus, we could get the latest one
and add it to the intall root to get the path of the latest version of CLR.

The following is  a sample.

using Microsoft.Win32;  

private string GetInstallRoot()
 {
           RegistryKey rk = Registry.LocalMachine;
           rk = rk.OpenSubKey("software\\microsoft\\.NetFramework",false);
           string installRoot = rk.GetValue("InstallRoot").ToString();
           return installRoot;
 }
 private string GetLatestVersion()
  {
           // Create a RegistryKey, which will access the
HKEY_LOCAL_MACHINE
           // key in the registry of this machine.
           RegistryKey rk = Registry.LocalMachine;
           rk = rk.OpenSubKey("software\\microsoft\\.NetFramework",false);

           // Retrieve all the subkeys for the specified key.
           String[] names = rk.GetSubKeyNames();

           string latestVersion = "";
           
           foreach (String name in names)
           {
               if (name.StartsWith("v") && name.CompareTo(latestVersion) >
0)
                   latestVersion = name;
           }

           return latestVersion;
  }

Then you could get the path of the latest version of CLR using the
following code.

string path = GetInstallRoot() + GetLatestVersion();

Hope this helps.
If you have any concerns, please feel free to let me know.

Sincerely,
Linda Liu
Microsoft Online Community Support

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