MetaData with InheritedExport

Question

Im trying to export all classes which implement an IJob interface while also passing metadata at the individual class level. What I've tried:

Export:

[InheritedExport(typeof(IJob))]
public interface IJob
{
    int Run();
}

Import:

    [ImportMany]
    public IEnumerable<Lazy<IJob, IJobMetaData>> Jobs { get; set; }

Implementation:

[IgnoreJob(false)]
public class MyJob : IJob
{
    public int Run()
    {
        return 5;
    }
}

Attribute setup:

[MetadataAttribute]
[AttributeUsage(AttributeTargets.Class, AllowMultiple = false)]
public class IgnoreJobAttribute : ExportAttribute, IJobMetaData
{
    public IgnoreJobAttribute(bool ignore)
        : base(typeof(IJobMetaData))
    {
        Ignore = ignore;
    }

    [DefaultValue(true)]
    public bool Ignore { get; set; }
}

The above does not pass my metadata but if I remove the InheritedExport attribute and add an Export attribute to the individual implementation of IJob it works fine...

Possible duplicate: http://stackoverflow.com/questions/6570930/how-to-use-mef-inherited-export-metadata — Simon Farshid, Sep 10 '14 at 16:44
unfortunately not! They at least had *some* metadata, I have none. — InContext, Sep 10 '14 at 16:52

score 1 · Accepted Answer · edited May 23 '17 at 11:49

Take a look at this: How to use MEF Inherited Export & MetaData?

It turns out that the metadata associated with your export must be available when the InheritedExport is being registered. MEF treats all exports that are made after inheriting from the given class as the same kind of export. Therefore, your metadata that is defined in the subclass is ignored.

So you are not able to use InheritedExport in this case, I'm afraid.

As I can see, you already inherit from ExportAttribute in your IgnoreJobAttribute, therefore, you should be able to drop the InheritedExportAttribute on the base class, as long as you keep a IgnoreJobAttribute on every IJob you define.

MetaData with InheritedExport

1 Answers1