单例模式的三种实现方法

第一种、双锁定法 

public sealed class Singleton
    {
        static Singleton instance = null;
        static readonly object lockhelper = new object();

        Singleton()
        {
        }

        public static Singleton Instance
        {
            get
            {
                if (instance == null)
                {
                    lock (lockhelper)
                    {
                        if (instance == null)
                        {
                            instance = new Singleton();
                        }
                    }
                }
                return instance;
            }
        }
    }

 

第二种、静态初始化

public sealed class Singleton
    {
        static readonly Singleton instance = new Singleton();

        static Singleton()
        {
        }

        Singleton()
        {
        }

        public static Singleton Instance
        {
            get
            {
                return instance;
            }
        }
    }

 

第三种、延时初始化

public sealed class Singleton
    {
        Singleton()
        {
        }

        public static Singleton Instance
        {
            get
            {
                return Nested.instance;
            }
        }

        class Nested
        {
            static Nested()
            {
            }

            internal static readonly Singleton instance = new Singleton();
        }
    }