I don't understand MEF very well, so hopefully this is a simple fix of how I think it works.

I'm trying to use MEF to get some information about a class and how it should be used. I'm using the Metadata options to try to achieve this. My interfaces and attribute looks like this:

public interface IMyInterface
{
}

public interface IMyInterfaceInfo
{
    Type SomeProperty1 { get; }
    double SomeProperty2 { get; }
    string SomeProperty3 { get; }
}

[MetadataAttribute]
[AttributeUsage(AttributeTargets.Class, AllowMultiple = true)]
public class ExportMyInterfaceAttribute : ExportAttribute, IMyInterfaceInfo
{
    public ExportMyInterfaceAttribute(Type someProperty1, double someProperty2, string someProperty3)
        : base(typeof(IMyInterface))
    {
        SomeProperty1 = someProperty1;
        SomeProperty2 = someProperty2;
        SomeProperty3 = someProperty3;
    }

    public Type SomeProperty1 { get; set; }
    public double SomeProperty2 { get; set; }
    public string SomeProperty3 { get; set; }
}

The class that is decorated with the attribute looks like this:

[ExportMyInterface(typeof(string), 0.1, "whoo data!")]
[ExportMyInterface(typeof(int), 0.4, "asdfasdf!!")]
public class DecoratedClass : IMyInterface
{
}

The method that is trying to use the import looks like this:

private void SomeFunction()
{
    // CompositionContainer is an instance of CompositionContainer
    var myExports = CompositionContainer.GetExports<IMyInterface, IMyInterfaceInfo>();
}

In my case myExports is always empty. In my CompositionContainer, I have a Part in my catalog that has two ExportDefinitions, both with the following ContractName: "MyNamespace.IMyInterface". The Metadata is also loaded correctly per my exports.

If I remove the AllowMultiple setter and only include one exported attribute, the myExports variable now has the single export with its loaded metadata.

What am I doing wrong?