Partial Classes

Partial Classes

Sometimes, we programmer need to create a big-may be better if I call it enormous-classes with a large number of class members. It will be difficult if we use single file to write down all the code.

C# provides partial keyword to enables partitioning classes. The declaration of a class can be partitioned among several partial class declarations.

• Each of the partial class declarations contains the declarations of some of the class members.
• The partial class declarations of a class can be in the same file or in different files.

Each partial declaration must be labeled as partial class, in contrast to the single keyword class. The declaration of a partial class looks the same as the declaration of a normal class, other than the addition of the type modifier partial.

Here's the example, in myEnourmousClass.cs file

using System;

namespace partial
{
    partial class myEnormousClass
    {
        public int myField1;

        public void myMethod1() 
        {
            Console.WriteLine("myField1 = " + myField1);
            Console.WriteLine("Code written in myEnormousClass.cs");
        }
    }
}

Meanwhile in myEnourmousClass2.cs, I write other myEnormousClass member, as following:

using System;

namespace partial
{
    partial class myEnormousClass
    {
        public float myField2;
        public void myMethod2()
        {
            Console.WriteLine("myField2 = " + myField2);
            Console.WriteLine("Code written in myEnormousClass2.cs");
        }
    }
}

In program.cs, I write Main method, as follow:

using System;

namespace partial
{
    class Program
    {
        static void Main(string[] args)
        {
            myEnormousClass myEnormousObject = new myEnormousClass() { myField1 = 425, myField2 = 73325.43F };
            myEnormousObject.myMethod1();
            myEnormousObject.myMethod2();
        }
    }
}

All the three code files will result

myField1 = 425
Code written in myEnormousClass.cs
myField2 = 73325,43
Code written in myEnormousClass2.cs

The type modifier partial is not a keyword, so in other contexts you can use it as an identifier in your program. But when used immediately before the keywords class, struct, or interface, it signals the use of a partial type.

Besides partial classes, you can also create two other partial types, those are: Partial structs and Partial interfaces.

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