Registration Free COM

From Windows XP SP2 Microsoft introduced a feature called RegFree COM, which allows you to call COM objects (yes some of us still use COM) without needing to register them first. The object in question must be in the same folder as the caller but this makes it much easier to install these objects and goes a little way to the xcopy distribution utopia. To use RegFree COM your caller and callee assemblies needs to have manifest files either externally or embedded - Manifest Files Reference. The assemblies can be written in any language that supports COM and you can call between languages, e.g. vb to vb, vb to .Net, .Net to vb.

The calling application needs a manifest file configured as follows, in this example the application is called MyApp.exe so the manifest is MyApp.exe.manifest:

<?xml version="1.0" encoding="UTF-8"?>
<assembly xmlns="urn:schemas-microsoft-com:asm.v1" manifestVersion="1.0">
  <assemblyIdentity type="win32" name="MyApp" version="0.0.0.0" />
  <dependency>
    <dependentAssembly>
      <assemblyIdentity type="win32" name="ComAssembly.dll" version="1.2.3.4" />
    </dependentAssembly>
  </dependency>
</assembly>

The COM assembly needs a manifest file configured as follows, in this example the assembly is called ComAssembly.dll so the manifest is ComAssembly.dll.manifest:

<?xml version="1.0" encoding="UTF-8"?>
<assembly xmlns="urn:schemas-microsoft-com:asm.v1" manifestVersion="1.0">
  <assemblyIdentity type="win32" name="ComAssembly.dll" version="1.2.3.4" />
  <file name="ComAssembly.dll">
    <comClass clsid="{11111111-2222-3333-4444-555555555555}" threadingModel="Both" />
  </file>
</assembly>

In MyApp.exe.manifest I have set the version to “0.0.0.0” this should really match the application version but “0.0.0.0” works. The dependentAssembly/assemblyIdentity  can be repeated for as many COM dependencies that you have.

The assemblyIdentity in the caller manifest must match exactly the one in the callee.

Getting this right can be quite difficult to debug, on XP the only clues to problems are written to the system eventlog with the source SideBySide. On Vista (and I assume Windows 7 and Windows Server 2008 although I haven’t tried it) you can use SxsTrace to help debug the problem. To start trace run “SxsTrace Trace -logfile:SxsTrace.etl” to convert the log file to something you can view run “SxsTrace Parse -logfile:SxsTrace.etl -outfile:SxsTrace.txt”.

The two manifest files presented here have been reduced to the minimum required to get the code to work, they are more settings that can be included see the Manifest Files Reference for more details.

See also:

• Simplify App Deployment with ClickOnce and Registration-Free COM
• Beth Massi - Sharing the goodness that is VB