C# Design Patterns: the Singleton pattern

January 13, 2009

Summary

A class that only allows one instance of itself, which is accessed via a static property.

Example usage

The commonest example is an application only allowing one instance of itself, much like Windows Media Player does. Another example is a ‘global’ instance of a class, which contains settings or config information.

This is Jon Skeet’s lazy implementation example. He has a full discussion on the various ways of implementing a singleton in C#, the example below being the final version. The full article can be found here

      
        public sealed class Singleton
      
        {
      
            Singleton()
      
        	{
      
        	}
      
        	public static Singleton Instance
      
        	{
      
        		get
      
        		{
      
        			return Nested.instance;
      
        		}
      
        	}
      
        	class Nested
      
        	{
      
        		// Explicit static constructor to tell C# compiler
      
        		// not to mark type as beforefieldinit
      
        		static Nested()
      
        		{
      
        		}
      
        		internal static readonly Singleton instance = new Singleton();
      
        	}
      
        }

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	public sealed class Singleton
	{
	Singleton()
	{
	}

	public static Singleton Instance
	{
	get
	{
	return Nested.instance;
	}
	}

	class Nested
	{
	// Explicit static constructor to tell C# compiler
	// not to mark type as beforefieldinit
	static Nested()
	{
	}
	internal static readonly Singleton instance = new Singleton();
	}
	}