C# で シングルトンパターン ref: http://qiita.com/rohinomiya/items/6bca22211d1bddf581c4

SamplaSingletonClass.cs

using System;

namespace SampleLog4Net
{
    /// <summary>
    /// Description of ClassNullLogger.
    /// </summary>
    public sealed class ClassNullLogger
    {
        private static ClassNullLogger instance = new ClassNullLogger();

        public static ClassNullLogger Instance {
            get {
                return instance;
            }
        }

        private ClassNullLogger()
        {
        }
    }
}

sample_singleton.cs

// Singletonパターン
public sealed class SingletonClass
{
    private static SingletonClass _singleInstance = new SingletonClass();

    public static SingletonClass GetInstance()
    {
        return _singleInstance;
    }

    private SingletonClass()
    {
        //TODO: initialization
    }
}