Providing delegate to MEF initialization

is it possible to provide a Lazy object initializer to a MEF container?

Here it is an example:

[Export]
public class Bar
{
  [ImportingConstructor[
  public Bar([Import] Lazy<Foo> foo)
  {
    // [..]
  }
}

TypeCatalog catalog = new TypeCatalog(typeof(Bar));
CompositionContainer container = new CompositionContainer(catalog);
Lazy<Foo> initializer = new Lazy(() =>
{
  Foo foo = new Foo();
  // foo initiali开发者_StackOverflow社区zation here
  return foo;
});
container.ComposeExportedValue(initializer);
CompositionBatch batch = new CompositionBatch();
container.Compose(batch);
var export = container.GetExportedValue<Bar>(); // composition fails

This piece of code doesn't work, while it works if I call container.ComposeExportedValue(new Foo()). I would like to directly pass a delegate to create the lazy object. Is it possible without the need for a custom export provider?

Thank you

Lazy<T> has a special meaning for MEF imports. Rather than looking literally for a Lazy<T> export, MEF will look for a T export and instantiate that part lazily.

Try to use this type instead for your imports and exports:

public class LazyPart<T> : Lazy<T>
{
    public LazyPart(Func<T> initializer) : base(initializer)
    {
    }
}

Since it is a different type, it should hold no special meaning for MEF.