C#

public interface IInstrumentService
{
    void Start();

    void Stop();

    void UpdateStatus(ServiceStatusModel status);
}

public class TestClass1 : IInstrumentService
{
    public void Start()
    {
    }

    public void Stop()
    {
    }

    public void UpdateStatus(ServiceStatusModel status)
    {
    }
}

private void GetServicesToLoadServices()
{
    string[] files = Directory.GetFiles(_servicesLocation, "*.dll");
    foreach (string file in files)
    {
        Assembly assembly = Assembly.LoadFrom(file);
        foreach (Type type in assembly.GetTypes())     //< == Type is "TestClass1" 
        {
            bool isImplementing1 = type.IsAssignableFrom(typeof(IInstrumentService));       //< ==  ALWAYS FALSE
            bool isImplementing2 = typeof(IInstrumentService).IsAssignableFrom(type);       //< ==  ALWAYS FALSE
        }
    }
}

MyCommand.Parameters.Add("@Mode", System.Data.SqlDbType.Text);
MyCommand.Parameters["@Mode"].Value = Convert.ToInt32(cbModePicker.SelectedItem.ToString());

In the below code snippet, Ring() method defined in Classes "SmartPhone", "BasicPhone" etc is returning a custom datatype called "Sound". As far as I have read few topics, custom datatypes can be implemented using Classes, Structures etc.Normally, I have worked with methods returning in-built datatypes like int,string etc but have no idea about methods returning custom datatypes like "Sound" as per mentioned example. So, how should I write/define the Class "Sound" for the above program to work

If code execution calls "Phone.Ring()" statement in the foreach loop defined Main() method , let's say a message "MP3 music is playing" for Smartphone, "Polyphonic music is playing" for SemiSmartPhone, "8BitMusic is playing" for BasicPhone to be displayed on the console screen. 
Let me know if you need more details.To be honest, had posted in other forums, but couldn't get an answer yet.As far as I remember, this code example has been picked from codeproject.com I believe.  Thanks

class Sound
{
    ???// What should the implementation of this class be for the program    
       //to work
}
interface IRingable
{
    public Sound Ring();
}
class SmartPhone : IRingable
{
    public Sound Ring()
    {
        return PlayMp3Music();

    }

}
class SemiSmartPhone : IRingable
{
    public Sound Ring()
    {
        return PolyPhonicMusic();
    }
}
class BasicPhone : IRingable
{
    public Sound Ring()
    {
        return 8BitMusic();
    }
}

class Main
{
    public static void Main(string[] args)
    {
        List<IRingable> phones = new List<IRingable>();
        IRingable htc = new SmartPhone();
        phones.Add(htc);
        IRingable samsung = new SemiSmartPhone();
        phones.Add(samsung);
        IRingable nokia = new BasicPhone();
        phones.Add(nokia);
        // Lets Ring them all
        foreach (IRingable phone in phones)
        {
            phone.Ring();
        }
    }
}