C# Partial Class and Partial Method

In C#, a class can be split into multiple files using the concept of partial classes. This allows developers to organize their code better and avoid having one large file for a class. Similarly, C# also allows partial methods, which allow developers to split a method into multiple parts across different files.

Partial Classes

A partial class is a class that is divided into multiple files. Each file contains a part of the class definition, and all parts together define the complete class. Partial classes are useful when you want to separate the implementation of a class into multiple files. For example, you can have one file for the class definition and another file for the implementation of its methods.

To define a partial class, you use the partial keyword before the class keyword. Here's an example:

1// MyClass.cs
2public partial class MyClass
3{
4    public void Method1() { }
5}
6
7// MyClass2.cs
8public partial class MyClass
9{
10    public void Method2() { }
11}

In this example, the MyClass class is split into two files, MyClass.cs and MyClass2.cs. Both files contain a part of the class definition, and the two parts together define the complete MyClass class.

Partial Methods

A partial method is a method that is divided into multiple parts across different files. A partial method has two parts: a declaration and an implementation. The declaration part is created in one file, and the implementation part is created in another file. Partial methods are used when you want to separate the implementation of a method into multiple files.

To define a partial method, you use the partial keyword before the void keyword. Here's an example:

1// MyClass.cs
2public partial class MyClass
3{
4    partial void MyMethod();
5}
6
7// MyClass2.cs
8public partial class MyClass
9{
10    partial void MyMethod()
11    {
12        // implementation
13    }
14}

In this example, the MyMethod method is split into two files, MyClass.cs and MyClass2.cs. The declaration part of the method is created in MyClass.cs, and the implementation part of the method is created in MyClass2.cs.

It's important to note that the implementation part of a partial method is optional. If you don't provide an implementation, the method is removed by the compiler, and any calls to the method are also removed.