How to manage discovery and composition as 2 separate concerns?

Question

I have set up an assembly catalog:

  private CompositionContainer GetContainer() {
     // initialize directory info
     ExtensionDirectory = new DirectoryInfo(         


        

Answer 1

In order to satisfy the requirements, I created 3 classes:

public sealed class CompositionFactory {
  [Import("Provider")]
  private IProvider importProvider;

  /* MEF initialization */
}

[Export("Provider")]
public sealed class AssemblyProvider : IProvider {
  private CatalogExportProvider _provider;
}

internal sealed class ComposableAggregate { }

The CompositionFactory initializes MEF to discover the AssemblyProvider. When the provider initializes:

private CatalogExportProvider InitializeProvider() {
   // directory catalog
   var dirCatalog = new DirectoryCatalog(ExtensionDirectory.FullName);
   return new CatalogExportProvider(dirCatalog);
}

...we return a CatalogExportProvider. I can now use an API to the CompositionFactory:

public ISomething GetSomething(string ContractName, object ContractParam) {
   // implementation
}

...to query for the correct composable part using a contract name:

public ComposablePartDefinition GetPartDefinition(string ContractName) {
   return _provider.Catalog.Parts
                   .Where(p => p.ExportDefinitions
                                .Select(e => e.ContractName)
                                .Any(c => c == ContractName))
                   .FirstOrDefault();
}

The work is then completed in the ComposableAggregate helper class:

internal ISomething Value {
   get {
      return _container.GetExport(_contractName).Value;
   }
}

private CompositionBatch CreateBatch() {
   CompositionBatch batch = new CompositionBatch();
   // create composable part from definition
   ComposablePart importDef = CreatePart(_contractName);
   batch.AddPart(importDef);
   return batch;
}

private ComposablePart CreatePart(string ContractName) {
   // get part definition from catalog
   return _provider.GetPartDefinition(ContractName).CreatePart();
}