Question

All tutorials I’ve read till now about Singleton pattern were as below :

 public sealed class Singleton
 {
      private static readonly Singleton instance = new Singleton();

      private Singleton(){}

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

but I already have a class in a assembly that I need to just have one instance of it during application lifetime . I don’t know how to use pattern mentioned above .

for example suppose there is a class X in dll named Y . is the code below correct :

 public sealed class Singleton
 {
      private static readonly Y.X instance = new Y.X();

      private Singleton(){}

      public static Y.X Instance
      {
         get 
         {
            return instance; 
         }
      }
 }

is this a true singleton ? if not , what is a correct way to handle this situation ?

Answer 1

No its not the singleton pattern. The fact that you are calling new Y.X() means anyone can call it. This does not specifically disallow new instances of Y.X()

However the code is okay if you need to make sure that you refer to only one instance of Y.X in your application. Then you can get it by calling Singleton.Instance.

This is in fact the Factory pattern (A class dedicated to creating objects), and I would suggest you call the class XFactory or something similar, instead of singleton.