Question

I have implemented the fusion.dll wrapper mentioned in many posts and now find that at least one dll I need to determine if it needs to be updated is not using build and revision numbers. Consequently I cannot compare on version numbers and need to compare on Last Modified date.

fusion.dll or it’s wrappers have no such method which I guess is fair enough but how do I determine the ‘real’ path of the dll so that I can discovers it’s last Modified date.

My code so far:

private DateTime getGACVersionLastModified(string DLLName)
{
  FileInfo fi = new FileInfo(DLLName);
  string dllName = fi.Name.Replace(fi.Extension, "");

  DateTime versionDT = new DateTime(1960,01,01);

  IAssemblyEnum ae = AssemblyCache.CreateGACEnum();
  IAssemblyName an;
  AssemblyName name;
  while (AssemblyCache.GetNextAssembly(ae, out an) == 0)
  {
    try
    {
      name = GetAssemblyName(an);

      if (string.Compare(name.Name, dllName, true) == 0)
      {
        FileInfo dllfi = new FileInfo(string.Format("{0}.dll", name.Name));
        if (DateTime.Compare(dllfi.LastWriteTime, versionDT) >= 0)
          versionDT = dllfi.LastWriteTime;
      }
    }
    catch (Exception ex)
    {
      logger.FatalException("Unable to get version number: ", ex);
    }
  }
  return versionDT;
}

Answer 1

From the problem description in your question I can see there are really 2 primary tasks that you are trying to accomplish:

1) Determine if a given assembly name can be loaded from the GAC.
2) Return the file modified date for the given assembly.

I believe these 2 points can be accomplished in a much simpler fashion and without having to work with the unmanaged fusion API. An easier way to go about this task might be as follows:

static void Main(string[] args)
{
  // Run the method with a few test values
  GetAssemblyDetail("System.Data"); // This should be in the GAC
  GetAssemblyDetail("YourAssemblyName");  // This might be in the GAC
  GetAssemblyDetail("ImaginaryAssembly"); // This just plain doesn't exist
}

private static DateTime? GetAssemblyDetail(string assemblyName)
{
  Assembly a;
  a = Assembly.LoadWithPartialName(assemblyName);
  if (a != null)
  {
    Console.WriteLine("'{0}' is in GAC? {1}", assemblyName, a.GlobalAssemblyCache);
    FileInfo fi = new FileInfo(a.Location);
    Console.WriteLine("'{0}' Modified: {1}", assemblyName, fi.LastWriteTime);
    return fi.LastWriteTime;
  }
  else
  {
    Console.WriteLine("Assembly '{0}' not found", assemblyName);
    return null;
  }
}

An example of the resulting output:

‘System.Data’ is in GAC? True
‘System.Data’ Modified: 10/1/2010 9:32:27 AM
‘YourAssemblyName’ is in GAC? False
‘YourAssemblyName’ Modified: 12/30/2010 4:25:08 AM
Assembly ‘ImaginaryAssembly’ not found