How to add instance of the class which satisfies import to CompositionContainer - mef

Question

I am facing the following problem:
var catalog = new AggregateCatalog();
catalog.Catalogs.Add(new AssemblyCatalog(typeof(Type1).Assembly));
catalog.Catalogs.Add(new AssemblyCatalog(typeof(Type2).Assembly));
using (CompositionContainer container = new CompositionContainer(catalog))
{
}
I need one more export:
Export[(typeof(Type3))]
The thing is that I can't include an assembly with the class which has this Export attribute. I want to tell the container that:
var myObject = new Type4();
myObject (the instance of Type4) should be exported each time the Import[(typeof(Type3))] is needed. Besides I can't mark Type4 with Export[(typeof(Type3))] and also I want the instance of the class to be used by MEF (so marking this class with Export attribute doesn't work, because I am changing myObject before I pass it to MEF and I want it to be used to satisfy Import).
Then when I try to do:
container.SatisfyImportsOnce(importer);
I expect that MEF will get all the objects from the assemblies in catalog, and for the missing Type3 it will use myObject. This should be the value when I do:
container.GetExportedValue<Type3>();
I spent one day trying different approaches: custom ExporterProvider and some sort of inheritance from Type4 to mark it with proper Export attribute but I can't get it working as I want.
I would be very grateful for help.
Thank you!

Answer 1

Ok, already found an answer.
First problem was that I added 2 the same AssemblyCatalogs to AggregateCatalog - don't do that.
The solution is to use CompositionBatch:
var catalog = new AggregateCatalog();
catalog.Catalogs.Add(new AssemblyCatalog(typeof(Type1).Assembly));
catalog.Catalogs.Add(new AssemblyCatalog(typeof(Type2).Assembly));
var myObject = new Type4();
using (CompositionContainer container = new CompositionContainer(catalog))
{
var batch = new CompositionBatch();
Export ex = CreateExport<Type3>(myObject); //Custom implementation
batch.AddExport(ex);
container.Compose(batch);
var val = container.GetExportedValue<Type3>(); //value == myObject
}
Thank you!