What is a singleton in C#?

Question

Pretty straight forward question.

What is a Singleton and when should I use it?

Answer 1

What it is: A class for which there is just one, persistent instance across the lifetime of an application. See Singleton Pattern.

When you should use it: As little as possible. Only when you are absolutely certain that you need it. I'm reluctant to say "never", but there is usually a better alternative, such as DI or simply a static class.

Answer 2

A singleton is a class which only allows one instance of itself to be created - and gives simple, easy access to said instance. The singleton premise is a pattern across software development.

There is a C# implementation here covering most of what you need to know - including some good advice regarding thread safety.

To be honest, It's very rare that you need to implement a singleton - in my opinion it should be one of those things you should be aware of, even if it's not used too often.

Answer 3

Here's what singleton is: http://en.wikipedia.org/wiki/Singleton_pattern

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 ;)

Answer 4

http://www.yoda.arachsys.com/csharp/singleton.html

Answer 5

Singleton is a design pattern.

Answer 6

It's a design pattern and it's not specific to c#. More about it all over the internet and SO, like on this wikipedia article.

In software engineering, the singleton pattern is a design pattern that is used to restrict instantiation of a class to one object. This is useful when exactly one object is needed to coordinate actions across the system. The concept is sometimes generalized to systems that operate more efficiently when only one object exists, or that restrict the instantiation to a certain number of objects (say, five). Some consider it an anti-pattern, judging that it is overused, introduces unnecessary limitations in situations where a sole instance of a class is not actually required, and introduces global state into an application.

You should use it if you want a class that can only be instanciated once.

Answer 7

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.

Answer 8

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.

Answer 9

You asked for C#. Trivial example:

public class Singleton
{
  private Singleton()
  {
    // Prevent outside instantiation
  }

  private static Singleton _singleton;

  public static Singleton GetSingleton()
  {
    if ( _singleton == null )
    {
      _singleton = new Singleton();
    }
    return _singleton;
  }
}

Answer 10

Everybody said about singleton,fair enough.Google says Singletons are Pathological Liars