Custom Extension Method In C#

public static class ExtensionMethodClass
{
    public static bool IsGreaterThan5(this int input)
    {
        bool result = false;
        if (input > 5)
        {
            result = true;
        }
        return result;
    }
}

Invoke in the same namespace' represents that the classes are presented within the same namespace with an extension method. It will be called by calling like other extension methods.

We have seen how to create an extension method and created the extension method in the name of "isGreaterThan5". Now, we will see how to call the extension method in our class. For a clear understanding, I am providing the screenshots.

using System;
namespace ExtensionMethod
{
    class Program
    {
        static void Main(string[] args)
        {
            Console.WriteLine("Enter Any Integer Value" + System.Environment.NewLine);
            int userInput = Convert.ToInt32(Console.ReadLine());
            bool result = userInput.IsGreaterThan5();
            Console.WriteLine("The result is " + result);
        }
    }
    public static class ExtensionMethodClass
    {
        public static bool IsGreaterThan5(this int input)
        {
            bool result = false;
            if (input > 5)
            {
                result = true;
            }
            return result;
        }
    }
}

Result

For more understanding, view the below image.

2. Invoke in Different Namespace

Now, we will see how to call the other namespace extension method in our class. Shall we move? For that, I am going to create one class library in the same solution.

Step 1. Create a new class library in the same solution.

Step 2. Create Extension Method(s).

Here, I have created an extension method to change the first char to uppercase from a given string.

public static class Class1
{
    public static string FirstCharToUpper(string input)
    {
        if (String.IsNullOrEmpty(input))
        {
            throw new ArgumentException("ArgumentException");
        }
        return input.First().ToString().ToUpper() + input.Substring(1);
    }
}

Step 3. Refer to the class library in your class. Right-click on the respective class to add the extension method class reference.

Step 4. Select Respective Class Library.

Here, we are adding the saying that we are selecting the reference from within the solution.

In the below image, you can see that the HereExtensionMethodExist class library is added as a reference to our respective class.

How to call the invoke the extension method action into class?

Step 1. Add a namespace in the header.

using HereExtensionMethodExist;

Step 2. We don't need to create an object, or we cannot create an object for the extension method.

using System; // Include the System namespace for Console
namespace YourNamespace // Replace YourNamespace with the actual namespace
{
    class Program
    {
        static void Main(string[] args)
        {
            Console.WriteLine("Enter Your Name");
            string userStringInput = Console.ReadLine();
            string stringResult = Class1.FirstCharToUpper(userStringInput);
            Console.WriteLine(stringResult);
        }
    }
}

Here, Class1 is the Class Library Class, and the FirstCharToUpper is our Extension Method.

Now, see the complete code in our class.

Console.WriteLine("Enter Any Integer Value" + System.Environment.NewLine);
int userInput = Convert.ToInt32(Console.ReadLine());
bool result = userInput.IsGreaterThan5();
Console.WriteLine("The result is " + result);
// Other Namespace Extension Method
Console.WriteLine("Enter Your Name");
string userStringInput = Console.ReadLine();
string stringResult = Class1.FirstCharToUpper(userStringInput);
Console.WriteLine(stringResult);

Result

Now, you can see both the results by using two extension methods.

Benefits of extension methods

• Extension methods allow existing classes to be extended without relying on inheritance or having to change the class's source code.
• If the class is sealed, then there is no concept of extending its functionality. For this, a new concept is introduced, in other words, extension methods.
• This feature is important for all developers, especially if you would like to use the dynamism of the C# enhancements in your class's design.
• And we can avoid code redundancy.

Summary

In this article, we learned how to create the extension method and all the ways we can access it.

I hope this was helpful to you. Your feedback and comments are always welcome.