C# Tutorials - Herong's Tutorial Examples

∟Partial Classes and Partial Methods

∟What Is Partial Class?

A quick introduction is provided on 'partial class', which declares an incomplete definition of a class. C# compile will merge multiple partial classes from multiple source files to form a complete class definition.

What Is Partial Class? A partial class is an incomplete definition of a class. C# supports partial class to allow developers to write a single class in multiple source files with each source file contains a partial definition of the class. Partial class definitions from multiple source files will be merged together by C# compile to form a complete class definition.

There several situations where partial class can be useful:

• In GUI applications, UI designers can implement the presentation part of the class in one source file. Logic developers can implement the business logic part of the same class in another source file.
• If a single class is implementing two interfaces, it can be separated into two source files, one for each interface implementation.

When coding partial class, we need to follow some rules, so that C# compile can merge multiple partial class definitions into a complete class:

• "partial class" must be used to declare a partial class.
• The class signature of the same partial class must be the same. For example, if partial class is declared as "abstract" in one source file, the same partial class must be declared as "abstract" in other source files.
• A single class member can only be declared in a single partial class.

For example, if we want to define class A in 2 source files: A1.cs and A2.cs, we can write the following in A1.cs:

// A1.cs
public partial class A {
  private int size;
  public static void Main() {
     ...
  }
  void method1() {
     ...
  }
}

And write the following in A2.cs:

// A2.cs
public partial class A {
  private float price;
  void method2() {
     ...
  }
  void method3() {
     ...
  }
}

Then we can compile them together to generate the executable program, A.exe:

C:\herong>csc /out:A.exe A1.cs A2.cs

Table of Contents

 About This Book

 Introduction of C# (C Sharp)

 Data Type and Variables

 Logical Expressions and Conditional Statements

 Arrays and Loop Statements

 Data Type Features

 Floating-Point Data Types

 Passing Parameters to Methods

 Execution Environment Class

 Visual C# 2010 Express Edition

 Class Features

 C# Compiler and Intermediate Language

 Compiling C# Source Code Files

 MSBuild - Microsoft Build Engine

 Memory Usages of Processes

 Multithreading in C#

 Async Feature from C# 5

 System.IO.FileInfo Class

 System.Diagnostics.FileVersionInfo Class

 WPF - Windows Presentation Foundation

►Partial Classes and Partial Methods

►What Is Partial Class?

 Partial Class Example

 What Is Partial Method?

 Partial Method Example

 Archived Tutorials

 References

 Full Version in PDF/ePUB

What Is Partial Class? - Updated in 2022, by Herong Yang