CSharp: Singleton Pattern

 

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/// <summary> /// Summary description for Spooler. /// geovindu,Geovin Du,涂聚文 /// 单例 模式（Singleton Patterns) /// </summary> public class Spooler {     /// <summary>     ///     /// </summary>     private static bool instance_flag = false;     /// <summary>     ///     /// </summary>     private Spooler()     {     }     /// <summary>     ///     /// </summary>     /// <returns></returns>     public static Spooler getSpooler()     {         if (!instance_flag)             return new Spooler();         else             return null;     }   }

　　

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/// <summary> /// Summary description for SingletonException. /// geovindu,Geovin Du,涂聚文 /// 单例 模式（Singleton Patterns) /// </summary> public class SingletonException : Exception {     /// <summary>     /// new exception type for singleton classes     /// </summary>     /// <param name="s"></param>     public SingletonException(string s)         : base(s)     {     } }

　　

调用测试：

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/// <summary>    /// geovindu,Geovin Du,涂聚文    /// 单例 模式（Singleton Patterns)    /// </summary>    public partial class SingletonPatternsForm : Form    {          /// <summary>        ///        /// </summary>        public SingletonPatternsForm()        {            InitializeComponent();        }        /// <summary>        ///        /// </summary>        /// <param name="sender"></param>        /// <param name="e"></param>        private void SingletonPatternsForm_Load(object sender, EventArgs e)        {          }        /// <summary>        ///        /// </summary>        /// <param name="sender"></param>        /// <param name="e"></param>        private void button1_Click(object sender, EventArgs e)        {            Spooler sp1 = Spooler.getSpooler();            if (sp1 != null)            {                this.textBox1.Text = "Got 1 spooler";                Console.WriteLine("Got 1 spooler");            }            Spooler sp2 = Spooler.getSpooler();            if (sp2 == null)            {                this.textBox2.Text = "Can\'t get spooler";                Console.WriteLine("Can\'t get spooler");            }            else            {                                 this.textBox2.Text = "Got 2 spooler";            }            //fails at compile time 不可访问，受保护级别           // Spooler sp3 = new Spooler();            }    }