AssemblyCatalog

AssemblyCatalog is a catalog implementation in the Managed Extensibility Framework (MEF) that exposes the exports declared in a single .NET assembly to a composition container. It uses reflection to inspect the types and members in the assembly for MEF export attributes, and it makes those exports available as parts that can be composed with imports in other parts of the application.

Typical usage involves creating an AssemblyCatalog by passing an Assembly instance (or a type from the assembly), constructing a CompositionContainer with that catalog, and then composing parts that declare imports. This allows an application to load and use plug-in components that expose exports without hard dependencies at compile time.

Compared with DirectoryCatalog, AssemblyCatalog focuses on one assembly rather than scanning a directory, which can improve performance and reduce the surface area of loaded parts. It is commonly used for plugin-like scenarios where a host application loads a known set of assemblies at startup or on demand.

Limitations include the need for the assemblies to be loadable in the current application domain, potential versioning issues, and a lack of built-in support for dynamic reloading; refreshing typically requires creating a new container or catalog. Security considerations apply, as loaded code runs with the host’s privileges and untrusted assemblies should be avoided.

See also MEF, CompositionContainer, ExportAttribute, ImportAttribute, DirectoryCatalog.