public interface ILogger {
  void LogMessage(string message);
}

public class DirectoryWatcher {
private ILogger _logger;
private FileSystemWatcher _watcher;
public DirectoryWatcher(ILogger logger) {
  _logger = logger;
  _watcher = new FileSystemWatcher(@ "C:Temp");
  _watcher.Changed += new FileSystemEventHandler(Directory_Changed);
}
void Directory_Changed(object sender, FileSystemEventArgs e) {
  _logger.LogMessage(e.FullPath + " was changed");
}
}

public class TextFileLogger: ILogger {
public void LogMessage(string message) {
  using(FileStream stream = new FileStream("log.txt", FileMode.Append)) {
   StreamWriter writer = new StreamWriter(stream);
   writer.WriteLine(message);
   writer.Flush();
  }
}
}

public class EventFileLogger: ILogger {
private string _sourceName;
public EventFileLogger(string sourceName) {
  _sourceName = sourceName;
}
public void LogMessage(string message) {
  if (!EventLog.SourceExists(_sourceName)) {
   EventLog.CreateEventSource(_sourceName, "Application");
  }
  EventLog.WriteEntry(_sourceName, message);
}
}

ILogger logger = new TextFileLogger();
DirectoryWatcher watcher = new DirectoryWatcher(logger);

ILogger logger = new EventFileLogger();
DirectoryWatcher watcher = new DirectoryWatcher(logger);

public class SimpleDIContainer {
Dictionary < Type, object > _map;
public SimpleDIContainer() {
   _map = new Dictionary < Type, object > ();
  }
/// <summary>
/// отображает тип интерфейса на реализацию этого интерфейса, с опционально присутствующими аргументами.
/// </summary>
/// <typeparam name="TIn">The interface type</typeparam>
/// <typeparam name="TOut">The implementation type</typeparam>
/// <param name="args">Optional arguments for the creation of the implementation type.</param>
public void Map <TIn, TOut> (params object[] args) {
   if (!_map.ContainsKey(typeof(TIn))) {
    object instance = Activator.CreateInstance(typeof(TOut), args);
    _map[typeof(TIn)] = instance;
   }
  }
/// <summary>
/// получает сервис, реализующий T
/// </summary>
/// <typeparam name="T">The interface type</typeparam>
public T GetService<T> () where T: class {
  if (_map.ContainsKey(typeof(T))) return _map[typeof(T)] as T;
  else throw new ApplicationException("The type " + typeof(T).FullName + " is not registered in the container");
}
}

public class SimpleDIContainer {
Dictionary <Type, object> _map;
public SimpleDIContainer() {
   _map = new Dictionary < Type, object > ();
  }
/// <summary>
/// отображает тип интерфейса на реализацию этого интерфейса, с опционально присутствующими аргументами.
/// </summary>
/// <typeparam name="TIn">The interface type</typeparam>
/// <typeparam name="TOut">The implementation type</typeparam>
/// <param name="args">Optional arguments for the creation of the implementation type.</param>
public void Map <TIn, TOut> (params object[] args) {
   if (!_map.ContainsKey(typeof(TIn))) {
    object instance = Activator.CreateInstance(typeof(TOut), args);
    _map[typeof(TIn)] = instance;
   }
  }
/// <summary>
/// получает сервис, реализующий T
/// </summary>
/// <typeparam name="T">The interface type</typeparam>
public T GetService <T> () where T: class {
  if (_map.ContainsKey(typeof(T))) return _map[typeof(T)] as T;
  else throw new ApplicationException("The type " + typeof(T).FullName + " is not registered in the container");
}
}