单例模式(Singleton Pattern)

介绍
保证一个类仅有一个实例，并提供一个访问它的全局访问点。

示例
保证一个类仅有一个实例。

　　Singleton

using System;
using System.Collections.Generic;
using System.Text;

namespace Pattern.Singleton
{
    /// <summary>
    /// 泛型实现单例模式
    /// </summary>
    /// <typeparam name="T">需要实现单例的类</typeparam>
    public class Singleton<T> where T : new()
    {
        /// <summary>
        /// 返回类的实例
        /// </summary>
        public static T Instance
        {
            get { return SingletonCreator.instance; }
        }

        class SingletonCreator
        {
            internal static readonly T instance = new T();
        }
    }
}

　　Test

using System;
using System.Data;
using System.Configuration;
using System.Collections;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;

using Pattern.Singleton;

public partial class Singleton : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        // 使用单例模式，保证一个类仅有一个实例
        Response.Write(Singleton<Test>.Instance.Time);
        Response.Write("<br />");
        Response.Write(Singleton<Test>.Instance.Time);
        Response.Write("<br />");

        // 不用单例模式
        Test t = new Test();
        Response.Write(t.Time);
        Response.Write("<br />");
        Test t2 = new Test();
        Response.Write(t2.Time);
        Response.Write("<br />");
    }
}

public class Test
{
    private DateTime _time;

    public Test()
    {
        System.Threading.Thread.Sleep(3000);
        _time = DateTime.Now;
    }

    public string Time
    {
        get { return _time.ToString(); }
    }
}

　　运行结果
　　2007-2-10 22:35:11
　　2007-2-10 22:35:11
　　2007-2-10 22:35:14
　　2007-2-10 22:35:17