MEF元数据应用说明

public interface IPluginMetadata
{
    string Name { get; }

    [DefaultValue(1)]  
    int Version { get; }
}

[Export(typeof(IPlugin)),
    ExportMetadata("Name", "Logger"),
    ExportMetadata("Version", 4)]
public class Logger : IPlugin
{
}

[Export(typeof(IPlugin)),
    ExportMetadata("Name", "Disk Writer")] 
    //Version is not required because of the DefaultValue
public class DWriter : IPlugin
{}

//----
public class Addin
{
    [Import]
    public Lazy<IPlugin, IPluginMetadata> plugin;
}
//-------

public class User
{
    [ImportMany]
    public IEnumerable<Lazy<IPlugin, IPluginMetadata>> plugins;

    public IPlugin InstantiateLogger ()
    {
        IPlugin logger = null;

        foreach (Lazy<IPlugin, IPluginMetadata> plugin in plugins)
        {
            if (plugin.Metadata.Name = "Logger") logger = plugin.Value;
        }
        return logger;
    }
}
//------