using System;

using System.Collections.Generic;

​

public interface IAchievementFeature

{

    string GetAchievement();

}

​

public class AchievementFeature : FeatureBase, IAchievementFeature

{

    public override void Init(){}

    public string GetAchievement()

    {

        return "achievement1";

    }

}

​

public class OnlineManager

{

    List<FeatureBase> features;

    public void AddFeature(FeatureBase feature)

    {

        features.Add(feature);

    }

    public T GetFeature<T>()

    {

        foreach(var feature in features)

        {

            if(feature.GetType() == typeof(T))

            {

                return (T)feature;  

            }

        }

        return null;

    }

}

​

public abstract class FeatureBase

{

    public abstract void Init();

}

public class Program

{

    public static void Main()

    {

        OnlineManager manager = new OnlineManager();

        AchievementFeature feature = new AchievementFeature();

        manager.AddFeature(feature);

        IAchievementFeature ifeature = manager.GetFeature<IAchievementFeature>();

    }

}