blocks|key|1130104|text|你要的是C#。简单的例子：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1130105|public+class+Singleton
{
++++private+Singleton()
++++{
++++++++//+Prevent+outside+instantiation
++++}

++++private+static+readonly+Singleton+_singleton+=+new+Singleton();

++++public+static+Singleton+GetSingleton()
++++{
++++++++return+_singleton;
++++}
}|code-block|syntax|javascript|1130106|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

You asked for C#. Trivial example:

<pre><code>
public class Singleton
{
 private Singleton()
 {
 // Prevent outside instantiation
 }

 private static readonly Singleton _singleton = new Singleton();

 public static Singleton GetSingleton()
 {
 return _singleton;
 }
}
</code></pre>

blocks|key|1345429|text|在c#中实现单例的另一种方式，我个人更喜欢这种方式，因为您可以将singeton类的实例作为属性而不是方法来访问。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1345430|public+class+Singleton
++++{
++++++++private+static+Singleton+instance;

++++++++private+Singleton()+{+}

++++++++public+static+Singleton+Instance
++++++++{
++++++++++++get
++++++++++++{
++++++++++++++++if+(instance+==+null)
++++++++++++++++++++instance+=+new+Singleton();
++++++++++++++++return+instance;
++++++++++++}
++++++++}

++++++++//instance+methods
++++}|code-block|syntax|javascript|1345431|但是，据我所知，这两种方式都被认为是“正确的”，所以这只是个人风格的事情。|1345432|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|L|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|M|8|@]|9|@]|A|$]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

another way to implement singleton in c#, i personally prefer this way because you can access the instance of the singeton class as a property instead of a method.

<pre><code>public class Singleton
 {
 private static Singleton instance;

 private Singleton() { }

 public static Singleton Instance
 {
 get
 {
 if (instance == null)
 instance = new Singleton();
 return instance;
 }
 }

 //instance methods
 }
</code></pre>

but well, as far as i know both ways are considered 'right' so it's just a thing of personal flavor.

blocks|key|1130046|text|单例(这与C#无关，它是一种OO设计模式)是指您希望在整个应用程序中只允许创建类的一个实例。使用通常包括全球资源，尽管我会说从个人经验来看，它们经常是巨大痛苦的来源。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1130047|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

A Singleton (and this isn't tied to C#, it's an OO design pattern) is when you want to allow only ONE instance of a class to be created throughout your application. Useages would typically include global resources, although I will say from personal experience, they're very often the source of great pain.

blocks|key|1130087|text|虽然单例只能有一个实例，但它与静态类不同。静态类只能包含静态方法，并且永远不能实例化，而单例的实例可以像使用任何其他对象一样使用。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1130088|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

Whilst the there can only ever be one instance of a singleton, it is not the same as a static class. A static class can only contain static methods and can never be instantiated, whereas the instance of a singleton may be used in the same way as any other object.

blocks|key|1345452|text|我用它来查找数据。从DB加载一次。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1345453|public+sealed+class+APILookup
++++{
++++++++private+static+readonly+APILookup+_instance+=+new+APILookup();
++++++++private+Dictionary<string,+int>+_lookup;

++++++++private+APILookup()
++++++++{
++++++++++++try
++++++++++++{
++++++++++++++++_lookup+=+Utility.GetLookup();
++++++++++++}
++++++++++++catch+{+}
++++++++}

++++++++static+APILookup()
++++++++{++++++++++++
++++++++}

++++++++public+static+APILookup+Instance
++++++++{
++++++++++++get
++++++++++++{
++++++++++++++++return+_instance;
++++++++++++}
++++++++}
++++++++public+Dictionary<string,+int>+GetLookup()
++++++++{
++++++++++++return+_lookup;
++++++++}

++++}|code-block|syntax|javascript|1345454|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

I use it for lookup data. Load once from DB. 

<pre><code>public sealed class APILookup
 {
 private static readonly APILookup _instance = new APILookup();
 private Dictionary&lt;string, int&gt; _lookup;

 private APILookup()
 {
 try
 {
 _lookup = Utility.GetLookup();
 }
 catch { }
 }

 static APILookup()
 { 
 }

 public static APILookup Instance
 {
 get
 {
 return _instance;
 }
 }
 public Dictionary&lt;string, int&gt; GetLookup()
 {
 return _lookup;
 }

 }
</code></pre>

blocks|key|1345284|text|单例是这样的：http://en.wikipedia.org/wiki/Singleton_pattern|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1345285|我不知道C#，但它实际上在所有语言中都是一样的，只是实现方式不同。|1345286|通常，在可能的情况下，您应该避免使用单例，但在某些情况下，这样做非常方便。|1345287|我的英语很抱歉;)|1345288|entityMap|0|LINK|mutability|MUTABLE|url|http://en.wikipedia.org/wiki/Singleton_pattern^0|7|1A|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|R|8|@]|9|@$A|S|B|T|1|U]]|C|$]]|$1|D|3|E|5|6|7|V|8|@]|9|@]|C|$]]|$1|F|3|G|5|6|7|W|8|@]|9|@]|C|$]]|$1|H|3|I|5|6|7|X|8|@]|9|@]|C|$]]|$1|J|3|-4|5|6|7|Y|8|@]|9|@]|C|$]]]|K|$L|$5|M|N|O|C|$P|Q]]]]

Here's what singleton is: <a href="http://en.wikipedia.org/wiki/Singleton_pattern" rel="nofollow noreferrer">http://en.wikipedia.org/wiki/Singleton_pattern</a>

I don't know C#, but it's actually the same thing in all languages, only implementation differs.

You should generally avoid singleton when it's possible, but in some situations it's very convenient.

Sorry for my English ;)

blocks|key|1345510|text|我知道现在回答这个问题已经很晚了，但是使用Auto-Property你可以这样做：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1345511|public+static+Singleton+Instance+{+get;+}+=+new+Singleton();|offset|length|style|CODE|1345512|其中Singleton是您的类，可以是via，在本例中为只读属性Instance。|1345513|entityMap^0|0|0|1O|0|2|9|W|8|0^^$0|@$1|2|3|4|5|6|7|L|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|M|8|@$D|N|E|O|F|G]]|9|@]|A|$]]|$1|H|3|I|5|6|7|P|8|@$D|Q|E|R|F|G]|$D|S|E|T|F|G]]|9|@]|A|$]]|$1|J|3|-4|5|6|7|U|8|@]|9|@]|A|$]]]|K|$]]

I know it's very late to answer the question but with Auto-Property you can do something like that:

<code>public static Singleton Instance { get; } = new Singleton();</code>

Where <code>Singleton</code> is you class and can be via, in this case the readonly property <code>Instance</code>.

blocks|key|1130270|text|线程安全单例，不使用锁，没有延迟实例化。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1130271|此实现具有静态构造函数，因此它在每个应用程序域中只执行一次。|1130272|public+sealed+class+Singleton
{

++++static+Singleton(){}

++++private+Singleton(){}

++++public+static+Singleton+Instance+{+get;+}+=+new+Singleton();

}|code-block|syntax|javascript|1130273|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|L|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|M|8|@]|9|@]|A|$G|H]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

Thread Safe Singleton without using locks and no lazy instantiation.

This implementation has a static constructor, so it executes only once per Application Domain.

<pre><code>public sealed class Singleton
{

 static Singleton(){}

 private Singleton(){}

 public static Singleton Instance { get; } = new Singleton();

}
</code></pre>

blocks|key|1130199|text|E.X您可以使用Singleton处理需要注入的全局信息。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1130200|在我的例子中，我保留了记录的用户详细信息(用户名、权限等)。在全局静态类中。当我尝试实现单元测试时，我无法将依赖项注入到控制器类中。因此，我将静态类更改为Singleton模式。|1130201|public+class+SysManager
{
++++private+static+readonly+SysManager_instance+=+new+SysManager();

++++static+SysManager()+{}

++++private+SysManager(){}

++++public+static+SysManager+Instance
++++{
++++++++get+{return+_instance;}
++++}
}|code-block|syntax|javascript|1130202|http://csharpindepth.com/Articles/General/Singleton.aspx#cctor|offset|length|1130203|entityMap|0|LINK|mutability|MUTABLE|url^0|0|0|0|0|1Q|0|0^^$0|@$1|2|3|4|5|6|7|T|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|U|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|V|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|W|8|@]|9|@$K|X|L|Y|1|Z]]|A|$]]|$1|M|3|-4|5|6|7|10|8|@]|9|@]|A|$]]]|N|$O|$5|P|Q|R|A|$S|J]]]]

E.X You can use Singleton for global information that needs to be injected.

In my case, I was keeping the Logged user detail(username, permissions etc.) in Global Static Class. And when I tried to implement the Unit Test, there was no way I could inject dependency into Controller classes. Thus I have changed my Static Class to Singleton pattern.

<pre><code>public class SysManager
{
 private static readonly SysManager_instance = new SysManager();

 static SysManager() {}

 private SysManager(){}

 public static SysManager Instance
 {
 get {return _instance;}
 }
}
</code></pre>

<a href="http://csharpindepth.com/Articles/General/Singleton.aspx#cctor" rel="nofollow noreferrer">http://csharpindepth.com/Articles/General/Singleton.aspx#cctor</a>

问什么是C#中的单例？
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