c# - Handle ReflectionTypeLoadException during MEF composition

Question

I am using a DirectoryCatalog in MEF to satisfy imports in my application. However, there are sometimes obfuscated assemblies in the directory that cause a ReflectionTypeLoadException when I try to compose the catalog.

I know I can get round it by using a separate directory or by using a search filter on the DirectoryCatalog but I want a more general way to solve the problem. Is there some way I can handle the exception and allow composition to continue? Or is there another more general solution?

Answer 1

To save others from writing their own implementation of the SafeDirectoryCatalog, here is the one I came up with based upon Wim Coenen's suggestions:

public class SafeDirectoryCatalog : ComposablePartCatalog
{
    private readonly AggregateCatalog _catalog;

    public SafeDirectoryCatalog(string directory)
    {
        var files = Directory.EnumerateFiles(directory, "*.dll", SearchOption.AllDirectories);

        _catalog = new AggregateCatalog();

        foreach (var file in files)
        {
            try
            {
                var asmCat = new AssemblyCatalog(file);

                //Force MEF to load the plugin and figure out if there are any exports
                // good assemblies will not throw the RTLE exception and can be added to the catalog
                if (asmCat.Parts.ToList().Count > 0)
                    _catalog.Catalogs.Add(asmCat);
            }
            catch (ReflectionTypeLoadException)
            {
            }
            catch (BadImageFormatException)
            {
            }
        }
    }
    public override IQueryable<ComposablePartDefinition> Parts
    {
        get { return _catalog.Parts; }
    }
}