二十三.单例模式

单例模式：

       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。

       类自身负责保存它的唯一实例。

注意：多线程

       使用锁，或C#静态类——Demo3

Demo1:——WinForm

       public partial class Form1 : Form

    {

       public Form1()

       {

           InitializeComponent();

       }

       private void Form1_Load(object sender, EventArgs e)

       {

           this.IsMdiContainer = true;

       }

       private void button1_Click(object sender, EventArgs e)

       {

           Form2.Show1().Show();

       }

    }

       public partial class Form2 : Form

    {

       private static Form2 f;

       private Form2()

       {

           InitializeComponent();

       }

       publicstatic Form2 Show1()

       {

           if (f == null || f.IsDisposed)

           {

                f = new Form2();

                f.MdiParent = Form1.ActiveForm;

           }

           return f;

       }

       private void Form2_Load(object sender, EventArgs e)

       {

       }

    }

Demo2:

       classProgram

    {

       static void Main(string[] args)

       {

           child c1= child.GetChild();

           child c2 = child.GetChild();

           c1.A = 5;

           Console.WriteLine(c2.A);

           Console.ReadKey();

       }

    }

   class child

    {

       private static child c;

       private child() { }

        public staticchild GetChild()

       {

           if (c == null)

           {

                c = new child();

           }

           return c;

       }

       private int a;

       public int A

       {

           get { return a; }

            set { a = value; }

       }

    }

Demo3:

1：

              privatestatic child c;

       private static readonly object syncRoot = newobject();//锁

       private child() { }

       public static child GetChild()

       {

           lock (syncRoot)

           {

                if (c == null)

               {

                    c = new child();

                }

           }

           return c;

       }

2：双重锁

       privatestatic child c;

       private static readonly object syncRoot = new object();//锁

       private child() { }

       public static child GetChild()

       {

           if (c == null)

            {

                lock (syncRoot)

                {

                    if (c == null)

                    {

                        c = new child();

                    }

                }

            }

           return c;

       }

3:静态类

              sealed class child//sealed声明静态类，阻止派生增加实例

    {

       privatestatic readonly child c=new child();//第一次引用类的任何成员时创建实例。公共语言运行库负责处理变量初始化

       private child() { }

       public static child GetChild()

       {

           returnc;

       }

       private int a;

       public int A

       {

           get { return a; }

           set { a = value; }

       }

    }