Singleton Class in C#: Explained with Example

Singleton Class in C# – What, Why & Real-World Use Case

In software development, especially when working with design patterns, you’ll eventually come across the singleton class in C#. It’s a commonly used design pattern that ensures only one instance of a particular class is created and used throughout the application’s lifecycle. This makes it ideal for scenarios like logging, configuration, or managing shared resources in a controlled way.

Let’s explore what a singleton class in C# is, when to use it, the pros and cons, and a relatable real-world example.

What is a Singleton Class?

A singleton class is a class that allows only one object (instance) to be created during the entire execution of a program. In C#, the Singleton pattern is implemented by making the constructor private and providing a static instance of the class.

Here’s a basic implementation:

public sealed class Logger
{
    private static readonly Logger _instance = new Logger();

    // Private constructor ensures no external instantiation
    private Logger() { }

    public static Logger Instance
    {
        get { return _instance; }
    }

    public void Log(string message)
    {
        Console.WriteLine($"Log: {message}");
    }
}

Now you can use it like this:

Logger.Instance.Log("Application started.");

This guarantees that the Logger object is created only once, no matter how many times it’s accessed.

Advantages of Singleton Class

1.Single Instance Across Application
Prevents multiple instances of a class, ensuring consistent behavior.

2.Global Access Point
The instance is accessible globally without needing to pass it around.

3.Resource Efficiency
Especially useful for classes managing system resources like database connections or file I/O.

4.Thread Safety
With proper implementation (like using readonly or lazy initialization), singletons can be made thread-safe.

Disadvantages of Singleton Class

1. Difficult to Unit Test
   Since the instance is tightly coupled, mocking it during tests becomes tricky.
2. Hidden Dependencies
   Code that uses singletons often hides its dependencies, which can lead to tight coupling.
3. Global State Risks
   Just like global variables, singleton instances can introduce unintended side effects if misused.

Real-World Example: Logger as Singleton

Let’s say you’re developing a web application and you want to log every activity. Creating a new logger instance each time would be inefficient. Instead, using a singleton ensures that all logs go through the same instance:

Logger.Instance.Log("User logged in");
Logger.Instance.Log("User updated profile");

This is clean, consistent, and performant. Plus, since logging is usually not instance-specific, it makes perfect sense to centralize it.

When Should You Use Singleton?

Use a singleton class in C# when:

• You need only one shared instance (e.g., configuration, caching, logging).
• The class manages shared resources.
• You want to prevent multiple initializations of the same object.

Avoid singletons if:

• You need multiple versions of the class for different scenarios.
• You want your class to be easily testable and loosely coupled.

Final Thoughts

The singleton class in C# is simple yet powerful. It’s ideal when you need one and only one instance of a class throughout your application. However, like any design pattern, it’s essential to use it wisely. Overusing singletons or using them in the wrong context can lead to tightly coupled, hard-to-test code.

By understanding when and how to use singletons, you can write cleaner, more maintainable, and efficient code.