Implement partial class in C#

Implementation of partial class

Let’s see how to define partial class in our own. We have to use partial keyword in front of class definition. 

using System;
using System.Collections;
using System.Data;
using System.Collections.Generic;
using System.Runtime.InteropServices;
namespace Test1
{
    partial class A
    {
        public void Partial_A()
        {
            Console.WriteLine("I am partial A");
        }
    }
    partial class A
    {
        public void Partial_B()
        {
             Console.WriteLine("I am other part of A");
        }
    }
 
    class Program
    {
        static void Main(string[] args)
        {
            A a = new A();
	    a.Partial_A();
            Console.ReadLine();
        }
    }
} 
 

In this example we have defined “A” class as partial class. So that, we are allowed to define “A” class more than one. But in behind (in IL code) .NET compiler combines both definitions in a single class. Below is the screen of IL code.

This is output screen of this code.

Is it needed to define all class in same file?

No, we can define partial class anywhere in project/application. It is not necessary to define in same file. In below example we will implement partial class in different .CS file but they must be in same namespace like below.

Code implementation is here.

In first .CS file

using System;
using System.Collections;
using Test1;
 
namespace Test1
{
    partial class A
    {
        public void Partial_A()
        {
            Console.WriteLine("First Part");
        }
    }
    partial class A
    {
        public void Partial_B()
        {
            Console.WriteLine("Second Part");
        }
    }
 
    class Program
    {
        static void Main(string[] args)
        {
            A a = new A();
	    a.Partial_A();
	    a.Partial_B();
	    a.Partial_C();
 
            Console.ReadLine();
        }
    }
}
 

In second .CS file

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
 
namespace Test1
{
    partial class A
    {
        public void Partial_C()
        {
            Console.WriteLine("Second Part");
        }
    }
}

Here is output screen.

Conclusion:

This is the example of partial class in C#. Hope you have understood the concept and enjoyed the article.