Question

I am planning to expose a .NET component with a COM interface, and I would like all the instances of the .NET class to share a single Application Domain.

What would be the best way of achieving that?

Answer 1

If it is possible it will not be easy.

While creating an instance of a type in a known AppDomain is easy (eg. Activator.CreateInstance overload that takes an AppDomain reference), the problem will be getting the reference to the target AppDomain.

Creating the AppDomain and sharing that reference within the current AppDomain is easy: a static field or property.

Sharing that reference to other AppDomains created by third party code is a problem. I seem to recall parts of the BCL do share statics across domains (essentially they have a single instance per process rather than per AppDomain, but this mechanism isn’t generally accessible to other assemblies.

It is probably better to understand why you want to be able to do this: there is probably a better solution to your underlying problem: why do you want all instances in a single AppDomain?