Partial class in C#

A partial class in C# allows you to split the definition of a class, struct, interface, or method across multiple files. This can be useful when working on large projects or when using auto-generated code, as it allows for organizing code in a way that separates auto-generated and manually written parts of the class. The partial keyword is used to specify that a class has been divided into parts.

Key Features of Partial Classes

1. Organizational Clarity: Keeps code cleaner by separating different functionalities or generated code from manually written code.
2. Team Collaboration: Multiple team members can work on the same class in different files without merging conflicts.
3. Auto-generated Code: Useful in cases where tools like Visual Studio generate code for you, as in Windows Forms or Entity Framework.

How to Use Partial Classes

To define a partial class, declare it using the partial keyword in each file where the class definition is split. Each file must have the same class name and be in the same namespace.

Example of Partial Class

Suppose you have a class Person split into two files, Person1.cs and Person2.cs:

File: Person1.cs

public partial class Person
{

    public string FirstName { get; set; }
    public string LastName { get; set; }
    public string GetFullName()
    {
        return $"{FirstName} {LastName}";
    }
}

File: Person2.c

public partial class Person
{
    public int Age { get; set; }
    public void DisplayInfo()
    {
        Console.WriteLine($"Name: {GetFullName()}, Age: {Age}");
    }
}

Both parts together make up the complete Person class, with FirstName, LastName, Age, and methods GetFullName and DisplayInfo.

Points to Remember

• All parts must use the partial keyword.
• All parts must have the same accessibility level (e.g., public, internal).
• If partial classes contain conflicting members, a compilation error will occur.
• The compiler combines all parts into a single class during compilation.

Use Cases

• Generated Code: Typically used when tools or frameworks generate part of the class.
• Large Classes: Split functionality for better organization, especially in large classes.

Partial classes are mainly used to improve code readability and maintainability, especially in projects where auto-generated code is prevalent or when dealing with large classes.