二十四种设计模式：单例模式(Singleton Pattern)

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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(); }

    }

}