单例

可以使用范型设计一个单例模板

public class Singleton<T> where T : Singleton<T>, new()
{
    static private T m_instance;
    static private readonly object m_lockObject = new object();


    protected Singleton()
    {
        Debug.Assert(m_instance == null, string.Format("{0} instance is Duplicated!", typeof(T).Name));
    }

    static public T Instance{
        get{
            if(m_instance != null)
                return m_instance;

            lock(m_lockObject)
            {
                if(m_instance != null)
                    return m_instance;

                m_instance = new T();                    
            }

            return m_instance;
        }
    }
}

此时使用Instance变量会访问到Singleton子类的所有public方法，如果我们只想对外公布指定的方法呢？使用接口

public class Singleton<T, I> where T : Singleton<T, I>, I, new()
{
    static private I m_instance;
    static private readonly object m_lockObject = new object();


    protected Singleton()
    {
        Debug.Assert(m_instance == null, string.Format("{0} instance is Duplicated!", typeof(T).Name));
    }

    static public I Instance{
        get{
            if(m_instance != null)
                return m_instance;

            lock(m_lockObject)
            {
                if(m_instance != null)
                    return m_instance;

                m_instance = new T();                    
            }

            return m_instance;
        }
    }
}

现在单例类只能访问到接口中定义的方法。