How to Implement Singleton Pattern Using C# (C Sharp)?
Singleton pattern falls under the roof of creational design patterns. You use singleton pattern in your code if you want to create only one instance of a class.
you might prefer to have only one printer spooler or single point of access
to your database. In such cases you can use this pattern. But ensure that
the instance created has to be globally accessed across all relevant pages
in your application. Singleton pattern can be implemented using C# in
multiple ways. Few of the most frequent ways are discussed in this article.
One way of
implementing singleton pattern is demonstrated below:
Output of this code will be:
is successfully created
In this example, sampleClass is your singleton class. In this class, you have made the constructor to be private. Hence you cannot directly create instance of sampleClass using new operator as shown below:
sampleclass obj = new sampleClass();
This statement will end up in compilation error.
In this example, you have a private static Boolean variable called flag which is false by default. If an instance of the class is created, then the flag will be set to true. When you are trying to get an instance next time, the flag value will be checked. Since it is true, only a null value will be sent instead of an instance creation. This logic is framed inside createInstance method. You can create an instance of sampleClass only by using this method.
In the above case, you have mentioned the constructor as private and posted the logic inside a class member method. You can also build the logic inside the constructor as shown in the example below:
this code will be:
In this method you have framed the entire logic inside the constructor. In addition, if you are trying to create another instance of the class then an exception will be thrown.
You can use
sealed classes to implement singleton pattern as shown below:
In this example, you have used sealed classes and class property to achieve the logic.
Ensure Global Access to the Instance:
So far you have been concentrating on how to implement singleton pattern in C# application code. But after implementing the pattern, you have to ensure that the class instance thus created is globally accessed across necessary pages in the application. For that, you can create the instance of the class and pass it to all relevant pages and classes as a parameter.
If you dont know which all pages/classes will access this instance then instead of passing it to all pages, you can create a registry containing all singleton classes of your application and ensure that the registry is accessible from all pages and classes.
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