compose exported value with mef with non-shared creation policy, but without specify it as attribute

Question

I have an instance of a class which I explicitly created and compose it to a CompositionContainer:

        container.ComposeExportedValue<ILogger>(_logger);

For some reasons, I had to create it explicitly and compose it. using export attribute isn't possible for me.

At every place I import that ILogger, I do it via ctor, for example:

public class A
{
    private readonly ILogger _logger;

    [ImportingConstructor]
    public A(ILogger logger)
    {
        this._logger = logger;
    }
}

In that way, I'll receive the same instance of ILogger every place I import it.

The question is, is it possible to configure that a new identical instance will be created for each time its being imported without using [PartCreationPolicy(CreationPolicy.NonShared)] attribute?

I'll remind you that using attributes isn't possible for me (otherwise I would simply used that attribute)

Answer 1

Try instead:

public class LoggerComposablePart : ComposablePart
{
    private readonly IEnumerable<ExportDefinition> exportDefinitions;

    public override IEnumerable<ExportDefinition> ExportDefinitions
    {
        get { return exportDefinitions; }
    }

    public override IEnumerable<ImportDefinition> ImportDefinitions
    {
        get { return Enumerable.Empty<ImportDefinition>(); }
    }

    public LoggerComposablePart()
    {
        Dictionary<string, object> metadata = new Dictionary<string, object>();

        metadata.Add(CompositionConstants.ExportTypeIdentityMetadataName, AttributedModelServices.GetTypeIdentity(typeof(ILogger)));
        metadata.Add(CompositionConstants.PartCreationPolicyMetadataName, CreationPolicy.NonShared);

        exportDefinitions = new ExportDefinition[] { new ExportDefinition(AttributedModelServices.GetContractName(typeof(ILogger)), metadata) };
    }

    public override object GetExportedValue(ExportDefinition definition)
    {
        // Create new logger instance for each import
        return new Logger();
    }

    public override void SetImport(ImportDefinition definition, IEnumerable<Export> exports)
    {
    }
}

Then eg:

CompositionBatch batch = new CompositionBatch();

batch.AddPart(new LoggerComposablePart());

container.Compose(batch);

var x = container.GetExportedValue<A>();