Doing magic with C# Method Extension

Say, we have a class defined in one of the assemblies shipped with a third party solution. It would be a great help if you could add a helper method to one of the objects. Unfortunately, we do not have the source code. 🙁 What do we do?

In such scenarios, .NET hasn’t left us alone in the desert 😀 The method extension technique will allow us to add our own methods to classes of our choice. Want to see an example? Take the List generics, every list of a generic type has some handy methods. Now we want to add one of ours. Printing each of the element in a list requires us to setup a foreach() loop every time. Why don’t we add an extension method named “Print()” which would print all the elements in a list – one by one? Let’s get our hands dirty!

Facts to remember:
— To extend a class and add method, we must declare a public static class with some name. The name doesn’t matter at all.
— We should define a method with our desired name in that class.
— The first parameter to the method will be “this < Object_we_want_to_extend > parameterName”. Do not forget the “this” keyword. It is the magic wand that does the magic.
— We can pass additional parameters.
— When calling the extended method from the original object, the first parameter is not required to pass. You can ignore it as if it were never there.
— For safety and security the extended method can not access private areas (fields, properties or methods).

So what do all these mean? Show me some codes! Okay, here you go:

using System;
using System.Collections.Generic;
using System.Linq;


namespace Test
{
    class Program
    {
        public static void Main(string[] args)
        {
            // Construct a list of "object" type. Setting the generic type to <object> will help us add all sorts of objects.
            List<object> list = new List<object>();

            // Add a string, integer and hell yeah - another list of string :D
            list.Add("masnun");
            list.Add(23);
            list.Add(new List<string>());

            // Lets call our extended method
            list.Print();

            // Halt the output until an enter is pressed. For a better examination of the output.
            Console.ReadLine();

        }
    }


    //The public static class with any name you choose
    public static class ListExtension
    {
        // The method name is Print. We're extending a generic here, so make the method follow.
        public static void Print<T>(this List<T> passedList)
        {
            // We loop through the generic and print the output of ToString()
            foreach (T x in passedList)
            {
                Console.WriteLine(x.ToString());
            }

        }
    }
}

using System;

using System.Collections.Generic;

using System.Linq;

namespace Test

{

class Program

{

public static void Main(string[] args)

{

// Construct a list of "object" type. Setting the generic type to <object> will help us add all sorts of objects.

List<object> list = new List<object>();

// Add a string, integer and hell yeah - another list of string :D

list.Add("masnun");

list.Add(23);

list.Add(new List<string>());

// Lets call our extended method

list.Print();

// Halt the output until an enter is pressed. For a better examination of the output.

Console.ReadLine();

}

//The public static class with any name you choose

public static class ListExtension

{

// The method name is Print. We're extending a generic here, so make the method follow.

public static void Print<T>(this List<T> passedList)

{

// We loop through the generic and print the output of ToString()

foreach (T x in passedList)

{

Console.WriteLine(x.ToString());

}

The output shall be:

masnun
23
System.Collections.Generic.List`1[System.String]

masnun

System.Collections.Generic.List`1[System.String]

Cool, no? 😀 The code is commented as much as I thought necessary. Feel free to ask a question or submit any feedback you might come up with 🙂

Have fun implementing some extended methods on your own 🙂

Recent Posts

Recent Comments

Archives

Categories