public class Control
{
  public string ID { get {return ""; } }
}

public interface IMyControl
{
  string ID { get; }
}

public class MyControl1 : Control, IMyControl
{
}

public sealed class MyControl2 : IMyControl
{
  public string ID { get { return ""; } }
}

public sealed class MyControl3 : Control
{
}

public class MyClass
{
  Control myControl1 = new MyControl1();
  MyControl2 myControl2 = new MyControl2();
  MyControl3 myControl3 = new MyControl3();

  public MyClass()
  {
    string id;
    id = myControl1.ID;
    id = myControl2.ID;
    id = myControl3.ID; // This reference shouldn't be found!
  }
}