Problem with MEF

Question

I have the folllowing:

private void ConfigureMEFContainer()
    {
        _catalog = new DirectoryCatalog(_pluginsPath);
        _container = new CompositionContainer(_catalog);
    }

       private readonly string _pluginsPath = Path.Combine(AppDomain.CurrentDomain.BaseDirectory, "Plugins");
    private DirectoryCatalog _catalog;
    private CompositionContainer _container;

Container is passed to another class:

        var batch = new CompositionBatch();
        batch.AddPart(this);

        container.Compose(batch);

        [ImportMany(typeof(IOnAnnotationCreatedPlugin))]
    public Lazy<IOnAnnotationCreatedPlugin, IAnnotationPluginMetadata>[] OnCreatedPlugins { get; set; }

    [ImportMany(typeof(IOnAnnotationCreatingPlugin))]
    public Lazy<IOnAnnotationCreatingPlugin, IAnnotationPluginMetadata>[] OnCreatingPlugins { get; set; }

    [ImportMany(typeof(IOnAnnotationUpdatedPlugin))]
    public Lazy<IOnAnnotationUpdatedPlugin, IAnnotationPluginMetadata>[] OnUpdatedPlugins { get; set; }

    [ImportMany(typeof(IOnAnnotationUpdatingPlugin))]
    public Lazy<IOnAnnotationUpdatingPlugin, IAnnotationPluginMetadata>[] OnUpdatingPlugins { get; set; }

All the collections above are empty!

Any help?

Answer 1

Thanks for your responses. I changed the code to the following and now it works fine. I believe, I had a problem with the custom Export Attribute and the Metadata interface. Here is the complete code in case someone else had the same problem:

public interface IAnnotationServicePluginMetadata
{
    string Name { get; }

    [DefaultValue(0)]
    int Priority { get; }
}

[MetadataAttribute]  
[AttributeUsage(AttributeTargets.Class, AllowMultiple=false)]  
public class AnnotationServicePluginMetadataAttribute : ExportAttribute  
{
   public AnnotationServicePluginMetadataAttribute()
       : base(typeof(IAnnotationServicePluginMetadata))
   {
   }  

   public string Name { get; set; }
   public int Priority { get; set; }
} 

Using the above:

[Export(typeof(IOnAnnotationUpdatedPlugin))]
[AnnotationServicePluginMetadata(Name = "OnUpdatedPlugin", Priority = 1)]
public class OnUpdatedPlugin : IOnAnnotationUpdatedPlugin
{ }

Properties as follows:

    [ImportMany(typeof(IOnAnnotationUpdatedPlugin))]
    public IEnumerable<Lazy<IOnAnnotationUpdatedPlugin, IAnnotationServicePluginMetadata>> OnUpdatedPlugins { get; set; }

Hope that helps. Regards