A simple C# dependency resolver class.

//
// Uttils/SimpleResolver.cs
// https://github.com/dropbox/DropboxBusinessAdminTool/blob/master/Source/DfBAdminToolkit.Common/Utils/SimpleResolver.cs
namespace DfBAdminToolkit.Common.Utils
{
    using System;
    using System.Collections.Generic;

    public class SimpleResolver
    {
        public static readonly SimpleResolver Instance = new SimpleResolver();
        private readonly Dictionary<Type, Type> _container;
        private readonly Dictionary<Type, object> _singleton;
        private static readonly object _lock = new object();

        private SimpleResolver()
        {
            _container = new Dictionary<Type, Type>();
            _singleton = new Dictionary<Type, object>();
        }

        public void Bind<ContractType>(Type implementer)
        {
            lock (_lock)
            {
                _container.Add(typeof(ContractType), implementer);
            }
        }

        public ContractType Get<ContractType>(params object[] args)
        {
            lock (_lock)
            {
                if (!_singleton.ContainsKey(typeof(ContractType)))
                {
                    ContractType obj = (ContractType)Activator.CreateInstance(_container[typeof(ContractType)], args);

                    _singleton.Add(typeof(ContractType), obj);
                }

                return (ContractType)_singleton[typeof(ContractType)];
            }
        }

        public void Dispose()
        {
            lock (_lock)
            {
                _singleton.Clear();
                _container.Clear();
            }
        }
    }
}

//
// Service Registration Example
//
// https://github.com/dropbox/DropboxBusinessAdminTool/blob/master/Source/DfBAdminToolkit/Program.cs
namespace DfBAdminToolkit
{
    using DfBAdminToolkit.Common.Utils;
    using DfBAdminToolkit.Model;
    using DfBAdminToolkit.Presenter;
    using DfBAdminToolkit.View;
    using Microsoft.Win32;
    using System;
    using System.Windows.Forms;

    internal static class Program
    {
        /// <summary>
        /// The main entry point for the application.
        /// </summary>
        [STAThread]
        private static void Main()
        {
            Application.EnableVisualStyles();
            Application.SetCompatibleTextRenderingDefault(false);

            Bind();

            // check legal acceptance status
            // if user hasn't accepted license term yet, force user to land on legal page first.
            bool userPreviouslyAcceptedLegalTerm = false;
            RegistryKey key = RegistryUtils.FindKey(ApplicationResource.RegistryEntryPoint);
            if (key != null)
            {
                // check acceptance status
                string value = RegistryUtils.GetKeyValue(key, ApplicationResource.RegistryKey);
                bool.TryParse(value, out userPreviouslyAcceptedLegalTerm);
            }

            if (userPreviouslyAcceptedLegalTerm)
            {
                IMainView appView = new MainView();
                IMainModel appModel = new MainModel();
                IMainPresenter presenter = SimpleResolver.Instance.Get<IMainPresenter>(
                    new object[] { appModel, appView }
                );

                Application.Run(appView as MainView);
            }
            else
            {
                // show legal view
                ILegalView legalView = new LegalView();
                ILegalModel legalModel = new LegalModel();
                ILegalPresenter presenter = SimpleResolver.Instance.Get<ILegalPresenter>(
                    new object[] { legalModel, legalView }
                );

                Application.Run(legalView as LegalView);
            }

            Unbind();
        }

        private static void Bind()
        {
            SimpleResolver.Instance.Bind<IMainPresenter>(typeof(MainPresenter));
            SimpleResolver.Instance.Bind<ILegalPresenter>(typeof(LegalPresenter));
            SimpleResolver.Instance.Bind<ITextSearchPresenter>(typeof(TextSearchPresenter));
            SimpleResolver.Instance.Bind<IDumpUserContentPresenter>(typeof(DumpUserContentPresenter));
            SimpleResolver.Instance.Bind<IProvisioningPresenter>(typeof(ProvisioningPresenter));
            SimpleResolver.Instance.Bind<IGroupsPresenter>(typeof(GroupsPresenter));
            SimpleResolver.Instance.Bind<ITeamFoldersPresenter>(typeof(TeamFoldersPresenter));
            SimpleResolver.Instance.Bind<IPaperPresenter>(typeof(PaperPresenter));
            SimpleResolver.Instance.Bind<IDevicesPresenter>(typeof(DevicesPresenter));
            SimpleResolver.Instance.Bind<ITeamHealthPresenter>(typeof(TeamHealthPresenter));
            SimpleResolver.Instance.Bind<ITeamAuditingPresenter>(typeof(TeamAuditingPresenter));
            SimpleResolver.Instance.Bind<IDataMigrationPresenter>(typeof(DataMigrationPresenter));
            SimpleResolver.Instance.Bind<ISettingsPresenter>(typeof(SettingsPresenter));
        }

        private static void Unbind()
        {
            SimpleResolver.Instance.Dispose();
        }
    }
}

//
// View/MainView.cs
//
// https://github.com/dropbox/DropboxBusinessAdminTool/blob/master/Source/DfBAdminToolkit/View/MainView.cs

private void SettingsToolStripMenuItem_Click(object sender, EventArgs e)
{
    ISettingsPresenter presenter = GetSettingPresenter();
    presenter.ShowSettings(this);
}

private DataMigrationView CreateDataMigrationView()
{
    IDataMigrationModel model = new DataMigrationModel();
    IDataMigrationView view = new DataMigrationView();
    IDataMigrationPresenter presenter = SimpleResolver.Instance.Get<IDataMigrationPresenter>(
        new object[] { model, view }
    );

    view.ShowView();

    return view as DataMigrationView;
}

private ISettingsPresenter GetSettingPresenter()
{
    ISettingsModel model = new SettingsModel();
    ISettingsView view = new SettingsView();
    ISettingsPresenter presenter = SimpleResolver.Instance.Get<ISettingsPresenter>(
        new object[] { model, view }
    );

    return presenter;
}