Partial Methods

Partial Methods

Partial methods are methods that are declared in different parts of a partial class. The different parts of the partial method can be declared in different parts of the partial class or in the same part. The two parts of the partial method are the following:

• The definition of partial method declaration
  • Lists the signature and return type.
  • There's no implementation code in declaration part.
• The implementation of partial method declaration
  • Lists the signature and return type.
  • The implementation is in the normal format, which, as you know, is a statement block.

The important things to know about partial methods are the following:

• The definition and implementation of methods must match in signature and return type. The signature and return type have the following characteristics:
  • The return type must be void.
  • The signature cannot include access modifiers, making partial methods implicitly private.
  • The parameter list cannot contain out parameters.
  • The contextual keyword partial must be included in both the definition and implementation of methods immediately before the keyword void.
• You can have a defining partial method without an implementing partial method. In this case, the compiler removes the declaration and any calls to the method made inside the class. You cannot have an implementing partial method without a defining partial method.

Lets add some partial method in previous myEnormousClass. myEnourmousClass.cs file:

using System;

namespace partial
{
    partial class myEnormousClass
    {
        public int myField1;
        partial void incMyFields();     //partial method definition 

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

Make incMyFields implementation in myEnourmousClass2.cs file.

using System;

namespace partial
{
    partial class myEnormousClass
    {
        public float myField2;
        partial void incMyFields()      //incMyFields implementation
        {
            ++myField1;
        }
        public void myMethod2()     
        {
            Console.WriteLine("myField2 = " + myField2);
            Console.WriteLine("Code written in myEnormousClass2.cs");
            incMyFields();              //Call incMyFields function
        }
    }
}

Now change the Main method, to check whether partial method works or not.

using System;

namespace partial
{
    class Program
    {
        static void Main(string[] args)
        {
            myEnormousClass myEnormousObject = new myEnormousClass() { myField1 = 425, myField2 = 73325.43F };
            myEnormousObject.myMethod1();
            myEnormousObject.myMethod2();
            myEnormousObject.myMethod1();   //check if partial method already works
            Console.Read();
        }
    }
}

Our modified code will be resulting:

myField1 = 425
Code written in myEnormousClass.cs
myField2 = 73325,43
Code written in myEnormousClass2.cs
myField1 = 426
Code written in myEnormousClass.cs

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