C# – MEF: ComposeParts missing

My question has been answered here.

Hi Nathan

There's a couple of different options here.

1. Using a batch, you can call the AddExportedObject method to add a mock instance to the container. AddExportedObject allows you to specify the contract for the instance that you are adding. i.e. batch.AddExportedObject(mockLogger, typeof(ILogger));

2. You an also create a custom export provider to allow you add mock instances. If you follow this link, here are some utils that I use. http://pastie.org/467842. Within you'll find a FakeExportProvider, along with FakeExportDefinitions. The FakeExportDefinitions take a func for the instance. This means you can pass it an instance, or even directly create a mock.

Here's sample code to illustrate usage.

    protected override void Context()
    {
        MockCache = MockRepository.GenerateStub<ICache>();
        var metadata = new Dictionary<string, object> ()
        var cacheDefinition = new FakeInstanceExportDefinition(typeof(ICache), MockCache, metadata);
        FakeProvider = new FakeExportProvider(f => ((FakeInstanceExportDefinition)f).Instance);
        FakeProvider.AddExportDefinitions(cacheDefinition);
        CacheExport = FakeProvider.GetExport<ICache>();
    }

Now above I am querying the export provider directly. However, our container allows passing in an export provider in it's construction. So you can do this...

var container = new CompositionContainer(null, FakeProvider).

HTH Glenn

What is failing? Is there an import you expect to be satisfied which is not being satisfied? Are you calling GetExports() and it is failing?

You can break in the debugger after the catalog has been created, and mouse over the aggregateCatalog variable to inspect it and see what parts are in it. My guess is that the parts are probably in the catalog, and the problem is somewhere else in your code. A likely cause is that you have a collection import which is using the [Import] attribute instead of [ImportMany], and/or that your parts are being rejected because they have imports that can't be satisfied.