Well I finally got around to diving into C#. Last week I spent a week with Richard Hale Shaw and 19 other coworkers going through a 5 day Visual Studio 2005 and .Net Framework 2.0 Bootcamp.
I won't rehash the usual arguments against managed custom actions. I'll assume your application already needs the .Net 2.0 Framework so that it really isn't a big deal to have to either bootstrap this and/or include in your LaunchCondition to require that it be installed.
So consider the following design pattern:
Server Side ( MSI context ):
Mixed Mode MC++ DLL that contains a standard call function and a .Net remotable object . We schedule the CA at the beginning of the InstallUISequence and InstallExecuteSequence. We will run the CA in Immediate Execution and msidbCustomActionTypeFirstSequence
and a that gets call at the beginning of the install. The SAO Singleton Remotable Object has wrapper methods for all of the MSI API functions that we want to call. When the Type 1 CA is invoked it starts up the CLR and hosts the remotable object. Next the custom action activates the object by passing the MSIHANDLE to a public property set accessor. Finally the custom action goes into a while loop checking once a second to see if a public property has been set to Exit indicating it's time to dispose and quit. Later in the install we will set the property to the exit setting.
The client side can be any managed code including run in any context. The managed code connects to the URI of the remotable object calling the MSI API wrapper method desired. The object is actually activated in the context of the server side which means it has access to the Installer Context.
The result is IPC using .Net Remoting and now you can write simple, powerful and robust Managed Code CA's with minimal plumbing to talk to the Installer.