c# - How to programmatically determine if .NET assembly is installed in GAC?

Question

What's the easiest way to check programmatically if an assembly is registered in the GAC (Global Assembly Cache) on the local machine? Is there some easy to use .NET API where I can give it a location to an assembly DLL or an Assembly object itself to check if it exists in GAC on the local machine? In my case the assembly I'm checking will already be loaded in the current AppDomain of the program checking so I'm not sure calling Assembly.ReflectionOnlyLoad and catching an exception will work like I've seen suggested in other posts, plus that seems kind of hacky.

Ideally I'd like to avoid calling an external executable like gacutil.exe to check.

Answer 1

This question is very similar to the following questions but mine is a little more precise, plus neither had an accepted answer and none of the answers offered seemed complete or optimal:

• Check GAC for an assembly
• Programmatically To check dll exists in Gac or not.If so display it in grid

Originally I thought the following was the best approach but it doesn't work unless you specify the full name of the assembly and it's kind of hacky beacause of the try/catch but it's simple and works for many cases:

public static class GacUtil
{
    public static bool IsAssemblyInGAC(string assemblyFullName)
    {
        try
        {
            return Assembly.ReflectionOnlyLoad(assemblyFullName)
                           .GlobalAssemblyCache;
        }
        catch
        {
            return false;
        }
    }

    public static bool IsAssemblyInGAC(Assembly assembly)
    {
        return assembly.GlobalAssemblyCache;
    }
}

This is a better approach that works without a try/catch by using the Fusion API. It's a bunch more code but it works with partial assembly names:

public static class GacUtil
{
    [DllImport("fusion.dll")]
    private static extern IntPtr CreateAssemblyCache(
        out IAssemblyCache ppAsmCache, 
        int reserved);

    [ComImport]
    [InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]
    [Guid("e707dcde-d1cd-11d2-bab9-00c04f8eceae")]
    private interface IAssemblyCache
    {
        int Dummy1();

        [PreserveSig()]
        IntPtr QueryAssemblyInfo(
            int flags, 
            [MarshalAs(UnmanagedType.LPWStr)] string assemblyName, 
            ref AssemblyInfo assemblyInfo);

        int Dummy2();
        int Dummy3();
        int Dummy4();
    }

    [StructLayout(LayoutKind.Sequential)]
    private struct AssemblyInfo
    {
        public int cbAssemblyInfo;
        public int assemblyFlags;
        public long assemblySizeInKB;

        [MarshalAs(UnmanagedType.LPWStr)]
        public string currentAssemblyPath;

        public int cchBuf;
    }

    public static bool IsAssemblyInGAC(string assemblyName)
    {
        var assembyInfo = new AssemblyInfo { cchBuf = 512 };
        assembyInfo.currentAssemblyPath = new string('', assembyInfo.cchBuf);

        IAssemblyCache assemblyCache;

        var hr = CreateAssemblyCache(out assemblyCache, 0);

        if (hr == IntPtr.Zero)
        {
            hr = assemblyCache.QueryAssemblyInfo(
                1, 
                assemblyName, 
                ref assembyInfo);

            if (hr != IntPtr.Zero)
            {
                return false;
            }

            return true;
        }

        Marshal.ThrowExceptionForHR(hr.ToInt32());
        return false;
    }
}