Question

What is the difference between the AddPart() and AddExport() in the composition batch class? When would I use one over the other?

Answer 1

I was wondering about the same thing and unfortunately haven’t been able to find any documentation that describes the difference between AddPart, AddExport, (and AddExportedValue) concisely. Here is what I have learned so far:

A part in MEF terminology, is a component that provides capabilities (aka exports) and specifies dependencies (aka imports).

So when you call batch.AddPart(something) then you are telling MEF that “something” is a component that may provide exports and depends on one or more imports.
If you call batch.AddExport(new Export("someExport", () => something)) then you are telling MEF that “something” is a component that just provides exports without requiring any imports, i.e. MEF will ignore any [Import] annotations that may be specified in the “something” class.

Internally AddExport actually calls AddPart, but prior to that it wraps the passed object in a “SingleExportComposablePart”, i.e. a ComposablePart returning an empty IEnumerable<ImportDefinition> on a call to ComposablePart.ImportDefinitions.