單例模式：

?????? 保證一個類僅有一個實(shí)例，并提供一個訪問它的全局訪問點(diǎn)。

?????? 類自身負(fù)責(zé)保存它的唯一實(shí)例。

注意：多線程

?????? 使用鎖，或C#靜態(tài)類——Demo3

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?

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;

???????}

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???????private void Form2_Load(object sender, EventArgs e)

???????{

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???????}

??? }

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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; }

???????}

??? }

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Demo3:

1：

????????????? privatestatic child c;

???????private static readonly object syncRoot = newobject();//鎖

???????private child() { }

???????public static child GetChild()

???????{

???????????lock (syncRoot)

???????????{

??????????????? if (c == null)

???????????????{

??????????????????? c = new child();

??????????????? }

???????????}

???????????return c;

???????}

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2：雙重鎖

?????? privatestatic child c;

???????private static readonly object syncRoot = new object();//鎖

???????private child() { }

???????public static child GetChild()

???????{

???????????if (c == null)

??????????? {

??????????????? lock (syncRoot)

??????????????? {

??????????????????? if (c == null)

??????????????????? {

??????????????????????? c = new child();

??????????????????? }

??????????????? }

??????????? }

???????????return c;

???????}

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3:靜態(tài)類

????????????? sealed class child//sealed聲明靜態(tài)類，阻止派生增加實(shí)例

??? {

???????privatestatic readonly child c=new child();//第一次引用類的任何成員時創(chuàng)建實(shí)例。公共語言運(yùn)行庫負(fù)責(zé)處理變量初始化

???????private child() { }

???????public static child GetChild()

???????{

???????????returnc;

???????}

???????private int a;

???????public int A

???????{

???????????get { return a; }

???????????set { a = value; }

???????}

??? }

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轉(zhuǎn)載于:https://www.cnblogs.com/yaoge/archive/2010/09/01/1815249.html

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