Singleton Class

Overview

• A Singleton class is a class that guarantees exactly one instance exists and provide a global access point to that instance.
• It has Private Constructor so user cannot create an instance of the class using new keyword.
• It has a static property that returns the single instance of the class. The instance is created when the class is loaded for the first time.
• sealed keyword is used to prevent inheritance of the Singleton class. so other classes cannot inherit from it and create multiple instances.

Use case

• Logging
• Configuration Settings
• License Manager

How it Different From Static Class?

Singleton Class	Static Class
Can be inherited	Cannot be inherited
Can implement interfaces	Cannot implement interfaces
Can be passed as parameter	Cannot be passed as parameter
Can be used as a reference type	Cannot be used as a reference type

Code

//Define Singleton Class
 internal sealed class Configuration
 {
     private Configuration()
     {
     }
     public static Configuration Instance { get; } = new Configuration();
     public string FloorName { get; set; }
     public int NumberOfFloors { get; set; }
     public override string ToString()
     {
         return $"Floor Name: {FloorName}, Number of Floors: {NumberOfFloors}";
     }
 }

//Use Singleton Class
 private static void Main()
 {
     var config = Configuration.Instance;
     config.FloorName = "Ground Floor";
     config.NumberOfFloors = 5;
     Console.WriteLine(config);

     var config2 = Configuration.Instance;
     config2.FloorName = "First Floor";
     config2.NumberOfFloors = 10;

     //Print original config to see if it has changed
     Console.WriteLine(config);
 }