C# Partial Class

In c#, a partial class is helpful to split the functionality of a particular class into multiple class files, and all these files will be combined into one single class file when the application is compiled.

While working on large-scale projects, multiple developers want to work on the same class file simultaneously. To solve this problem, c# provides an ability to spread the functionality of a particular class into multiple class files using partial keyword.

In c#, we can use partial keyword to split the definition of a particular class, structure, interface, or method over two or more source files.

Following is the example of splitting the definition of User class into two class files, User1.cs and User2.cs.

User1.cs

public partial class User
 {
    private string name;
    private string location;
    public User(string a, string b)
    {
        this.name = a;
        this.location = b;
    }
 }

If you observe the above code, we created a partial class called User in User1.cs class file using partial keyword with required variables and constructor.

User2.cs

public partial class User
 {
     public void GetUserDetails()
     {
        Console.WriteLine("Name: " + name);
        Console.WriteLine("Location: " + location);
     }
 }

If you observe the above code, we created a partial class called User in User2.cs class file using partial keyword with GetUserDetails() method.

When you execute the above code, the compiler will combine these two partial classes into one User class as shown below.

User

public class User
 {
    private string name;
    private string location;
    public User(string a, string b)
    {
        this.name = a;
        this.location = b;
    }
    public void GetUserDetails()
    {
        Console.WriteLine("Name: " + name);
        Console.WriteLine("Location: " + location);
    }
 }

This is how the compiler will combine all the partial classes into a single class while executing the application in the c# programming language.

Rules to Implement Partial Class

In c#, we need to follow certain rules to implement a partial class in our applications.

To split the functionality of class, structure, interface, or method over multiple files, we need to use partial keyword and all files must be available at compile time to form the final type.
The partial modifier can only appear immediately before the keywords class, struct, or interface.
All parts of partial type definitions must be in the same namespace or assembly.
All parts of partial type definitions must have the same accessibility, such as public, private, etc.
If any partial part is declared as abstract, sealed, or base, then the whole type is considered abstract or sealed, or base based on the defined type.
As discussed in the inheritance concept, in c# a class can have a single base class so the partial classes that we create for a particular class must inherit from the same base class.
Nested partial types are allowed in partial type definitions.

C# Partial Class Example

Following is the example of defining partial classes using partial keyword in c# programming language.

using System;

 namespace Tutlane
 {
     public partial class User
     {
         private string name;
         private string location;
         public User(string a, string b)
         {
            this.name = a;
            this.location = b;
         }
     }
     public partial class User
     {
         public void GetUserDetails()
         {
            Console.WriteLine("Name: " + name);
            Console.WriteLine("Location: " + location);
         }
     }
     class Program
     {
        static void Main(string[] args)
        {
            User u = new User("Suresh Dasari", "Hyderabad");
            u.GetUserDetails();
            Console.WriteLine("\nPress Enter Key to Exit..");
            Console.ReadLine();
        }
     }
 }

If you observe the above example, we created a partial class User using partial keyword and we are able to access all partial classes as a single class to perform required operations.

When you execute the above c# program, we will get the result below.

C# Partial Class Example Result