MEF plugins have no data from host

I'm trying to put config data from host to plugins but I always get nulls at plugins. My code responsible for plugins is below:

Form:

public partial class MyForm : Form
{
    public MyForm()
    {
        InitializeComponent();

        DataStorage.Instance.LoadModes();
        DataStorage.Instance.ActiveMode = "aaa";
        DataStorage.Instance.RulesFile = "bbb";
        DataStorage.Instance.SetProjectName("cccc");
        DataStorage.Instance.LoadRules();
        DataStorage.Instance.LoadPlugins();

    }
}

DataStorage:

[PartCreationPolicy(CreationPolicy.Shared)]
[Export(typeof(ConfigStorage))]  
public class DataStorage: ConfigStorage
{

    //fields and properties here

    public string ActiveMode;

    [ImportMany(typeof (IAPlugin))]
    public IEnumerable<Lazy<IAPlugin, IAPluginData>> aPlugins;

    [ImportMany(typeof (IBPlugin))]
    public IEnumerable<Lazy<IBPlugin, IBPluginData>> bPlugins;

    private CompositionContainer _container;

    private sta开发者_StackOverflow中文版tic readonly DataStorage instance = new DataStorage();

    static DataStorage()
    {
    }

    private DataStorage()
    {
            Init();
    }


    public static DataStorage Instance
    {
        get { return instance; }
    }


    private void Init()
    {
        //code here
    }

    public void LoadPlugins()
    {
        var catalog = new AggregateCatalog();
        catalog.Catalogs.Add(new AssemblyCatalog(typeof(ConfigStorage).Assembly));
        catalog.Catalogs.Add(new DirectoryCatalog(Settings.Default.GetPathFor("Plugins")));

        _container = new CompositionContainer(catalog);

        try
        {
            _container.ComposeParts(this);
        }
        catch (CompositionException compositionException)
        {
            Console.WriteLine(compositionException.ToString());
        }
    }
}

ConfigStorage:

public abstract class ConfigStorage
{

    public string RulesFile;
    public string ActiveMode;
//properties and methods
}

Plugin:

[Export(typeof (IAPlugin))]
[ExportMetadata("Name", "myNameIsBond")]
public class myNameIsBond :  IAPlugin
{

     protected readonly ConfigStorage configStorage;

     [ImportingConstructor]
     public myNameIsBond (ConfigStorage configStorage)
    {
        if (configStorage == null)
            throw new ArgumentNullException("configStorage");
        this.configStorage = configStorage;
    }


    public string DoStep(string url)
    {
        Console.WriteLine(configStorage.ActiveMode); //this is null - it should be "aaa"
        return url;
    }

}

When I run plugin.Value.DoStep("sth"); the Console.WriteLine(configStorage.ActiveMode); always print null - when I debugging: all fields from configStorage are nulls. What I'm doing wrong? How can I put DataStorage instance to my plugins?

I think the problem is that the ConfigStorage export is showing up in the catalog, so the imports are getting satisfied with a version created by the catalog instead of the singleton you have configured. Try putting a PartNotDiscoverableAttribute on the DataStorage class.

As an aside, your DataStorage constructor is private, but it looks like the catalog can still create a separate version of it because the constructor is invoked through reflection.

I typically don't use an instance variable at all and just let MEF create the singleton, but if you really want to have an instance property you can do something like

// note that there is no export attribute here
public class DataStorage: ConfigStorage
{
    [Export(typeof(ConfigStorage))] 
    public static DataStorage instance { get; private set; }
}

So that MEF will export your singleton instance rather than creating a new object.