[Solved] List of classes in an assembly C#

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Here’s a little class I whipped up some weeks back when I was bored, this does what you’re asking of – if I understand the question correctly.

Your applications must implement IPlugin, and must be dropped in a “Plugins” folder in the executing directory.

public interface IPlugin
{
    void Initialize();
}
public class PluginLoader
{
    public List<IPlugin> LoadPlugins()
    {
        List<IPlugin> plugins = new List<IPlugin>();

        IEnumerable<string> files = Directory.EnumerateFiles(Path.Combine(Directory.GetCurrentDirectory(), "Plugins"),
            "*.dll",
            SearchOption.TopDirectoryOnly);

        foreach (var dllFile in files)
        {
            Assembly loaded = Assembly.LoadFile(dllFile);

            IEnumerable<Type> reflectedType =
                loaded.GetExportedTypes().Where(p => p.IsClass && p.GetInterface(nameof(IPlugin)) != null);

            plugins.AddRange(reflectedType.Select(p => (IPlugin) Activator.CreateInstance(p)));
        }

        return plugins;
    }
}

Following from Paul’s recommendation in the comments, here’s a variation using MEF, referencing the System.ComponentModel.Composition namespace.

namespace ConsoleApplication18
{
    using System;
    using System.ComponentModel.Composition;
    using System.ComponentModel.Composition.Hosting;
    using System.IO;
    using System.Linq;

    public interface IPlugin
    {
        void Initialize();
    }
    class Program
    {
        private static CompositionContainer _container;
        static void Main(string[] args)
        {
            AggregateCatalog catalog = new AggregateCatalog();
            catalog.Catalogs.Add(new DirectoryCatalog(Path.Combine(Directory.GetCurrentDirectory(), "Plugins")));

            _container = new CompositionContainer(catalog);

            IPlugin plugin = null;
            try
            {
                _container.ComposeParts();

                // GetExports<T> returns an IEnumerable<Lazy<T>>, and so Value must be called when you want an instance of the object type.
                plugin = _container.GetExports<IPlugin>().ToArray()[0].Value;
            }
            catch (CompositionException compositionException)
            {
                Console.WriteLine(compositionException.ToString());
            }

            plugin.Initialize();
            Console.ReadKey();
        }
    }
}

and the DLL file – also referencing the System.ComponentModel.Composition namespace to set the ExportAttribute

namespace FirstPlugin
{
    using System.ComponentModel.Composition;

    [Export(typeof(IPlugin))]
    public class NamePlugin : IPlugin
    {
        public void Initialize() { }
    }
}

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solved List of classes in an assembly C#