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C# Partial (How It Works For Developers)

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Chipego Kalinda

April 29, 2024

C# offers a unique feature that enhances the organization and management of code in larger projects: the partial keyword class. This feature, accessible via the partial modifier, allows developers to split the definition of a class, interface, or struct across multiple files. This capability is particularly beneficial for working with already generated source code, such as user interface control definitions or service wrapper code, alongside custom business logic. In this article, we'll learn about partial classes and the IronPDF PDF Library for .NET using Visual Studio.

Understanding Partial Class

A partial class, maintaining the same accessibility level, is defined with the partial modifier in C#, indicating that the class definition is spread out over two or more files within the same assembly. This approach keeps related code together while maintaining separation of concerns. For example, a partial class Employee might have its business logic in one file and its data access layer in another, yet both parts are compiled into a single class. This separation not only makes the code more manageable but also allows multiple developers to work on the same class without conflict.

// File 1: Employee_BusinessLogic.cs
public partial class Employee
{
    public void CalculatePay() { /* Implementation */ }
}
// File 2: Employee_DataAccess.cs
public partial class Employee
{
    public void Load() { /* Implementation */ }
}

// File 1: Employee_BusinessLogic.cs
public partial class Employee
{
    public void CalculatePay() { /* Implementation */ }
}
// File 2: Employee_DataAccess.cs
public partial class Employee
{
    public void Load() { /* Implementation */ }
}

' File 1: Employee_BusinessLogic.cs
Partial Public Class Employee
	Public Sub CalculatePay()
	End Sub
End Class
' File 2: Employee_DataAccess.cs
Partial Public Class Employee
	Public Sub Load()
	End Sub
End Class

Leveraging Partial Methods

Partial classes can also define partial methods, which are optional or even declared abstract, allowing for more flexible implementation strategies. These methods enable an interesting scenario where part of the class can declare a method without implementing it, allowing another part of the class to implement it. If no implementation is provided, the partial method call is removed at compile time, resulting in no performance penalty.

// File 1: Employee_BusinessLogic.cs
public partial class Employee
{
    partial void OnPayCalculated(double amount);
    public void CalculatePay()
    {
        double amount = 1000; // Simplified calculation
        OnPayCalculated(amount);
    }
}
// File 2: Employee_Events.cs
public partial class Employee
{
    partial void OnPayCalculated(double amount)
    {
        Console.WriteLine($"Pay calculated: {amount}");
    }
}

// File 1: Employee_BusinessLogic.cs
public partial class Employee
{
    partial void OnPayCalculated(double amount);
    public void CalculatePay()
    {
        double amount = 1000; // Simplified calculation
        OnPayCalculated(amount);
    }
}
// File 2: Employee_Events.cs
public partial class Employee
{
    partial void OnPayCalculated(double amount)
    {
        Console.WriteLine($"Pay calculated: {amount}");
    }
}

' File 1: Employee_BusinessLogic.cs
Partial Public Class Employee
	Partial Private Sub OnPayCalculated(ByVal amount As Double)
	End Sub
	Public Sub CalculatePay()
		Dim amount As Double = 1000 ' Simplified calculation
		OnPayCalculated(amount)
	End Sub
End Class
' File 2: Employee_Events.cs
Partial Public Class Employee
	Private Sub OnPayCalculated(ByVal amount As Double)
		Console.WriteLine($"Pay calculated: {amount}")
	End Sub
End Class

Advanced Use of Partial Methods

Partial methods, embodying a partial definition approach, are a special feature within partial classes that allow for a declaration in one part of a partial class and an optional implementation in another. This feature is particularly useful for providing hooks in generated code that can be optionally implemented by the developer. The partial keyword is crucial here, as it signifies that the method may or may not have an implementation.

Consider an example where a UI component needs to perform some action before a user interface control is loaded. The partial method provides a clean way to insert custom business logic without cluttering the auto-generated code.

// File: UIControls_AutoGenerated.cs
public partial class UIControls
{
    partial void OnControlLoading();
    public void LoadControl()
    {
        OnControlLoading();
        // Auto-generated loading logic here
    }
}
// File: UIControls_CustomLogic.cs
public partial class UIControls
{
    partial void OnControlLoading()
    {
        // Custom business logic code here
        Console.WriteLine("Custom control loading logic executed.");
    }
}

// File: UIControls_AutoGenerated.cs
public partial class UIControls
{
    partial void OnControlLoading();
    public void LoadControl()
    {
        OnControlLoading();
        // Auto-generated loading logic here
    }
}
// File: UIControls_CustomLogic.cs
public partial class UIControls
{
    partial void OnControlLoading()
    {
        // Custom business logic code here
        Console.WriteLine("Custom control loading logic executed.");
    }
}

' File: UIControls_AutoGenerated.cs
Partial Public Class UIControls
	Partial Private Sub OnControlLoading()
	End Sub
	Public Sub LoadControl()
		OnControlLoading()
		' Auto-generated loading logic here
	End Sub
End Class
' File: UIControls_CustomLogic.cs
Partial Public Class UIControls
	Private Sub OnControlLoading()
		' Custom business logic code here
		Console.WriteLine("Custom control loading logic executed.")
	End Sub
End Class

Integrating Business Logic with Partial Classes

Business logic often requires modification and extension beyond what is automatically generated, especially in applications with complex rules or behaviors. Partial classes provide a seamless way to include business logic in a separate source file without altering the auto-generated UI or data access code. This separation ensures that the business logic is easily accessible and modifiable by developers, enhancing collaboration, especially when more than one developer is working on the project.

// File: Employee_AutoGenerated.cs
public partial class Employee
{
    // Auto-generated properties and methods
}
// File: Employee_BusinessLogic.cs
public partial class Employee
{
    public void Promote()
    {
        // Business logic code to promote an employee
        Console.WriteLine("Employee promoted.");
    }
}

// File: Employee_AutoGenerated.cs
public partial class Employee
{
    // Auto-generated properties and methods
}
// File: Employee_BusinessLogic.cs
public partial class Employee
{
    public void Promote()
    {
        // Business logic code to promote an employee
        Console.WriteLine("Employee promoted.");
    }
}

' File: Employee_AutoGenerated.cs
Partial Public Class Employee
	' Auto-generated properties and methods
End Class
' File: Employee_BusinessLogic.cs
Partial Public Class Employee
	Public Sub Promote()
		' Business logic code to promote an employee
		Console.WriteLine("Employee promoted.")
	End Sub
End Class

Nesting Partial Types

Nested partial types extend the concept of partial classes to nested classes, allowing parts of a nested class to be defined in separate files. This can be particularly useful for organizing large nested structures, such as a complex user interface control definition that includes multiple nested types for handling various aspects of the control's behavior.

// File: ComplexControl_Part1.cs
public partial class ComplexControl
{
    public partial class NestedControl
    {
        public void Initialize() { /* Initialization code here */ }
    }
}
// File: ComplexControl_Part2.cs
public partial class ComplexControl
{
    public partial class NestedControl
    {
        public void Cleanup() { /* Cleanup code here */ }
    }
}

// File: ComplexControl_Part1.cs
public partial class ComplexControl
{
    public partial class NestedControl
    {
        public void Initialize() { /* Initialization code here */ }
    }
}
// File: ComplexControl_Part2.cs
public partial class ComplexControl
{
    public partial class NestedControl
    {
        public void Cleanup() { /* Cleanup code here */ }
    }
}

' File: ComplexControl_Part1.cs
Partial Public Class ComplexControl
	Partial Public Class NestedControl
		Public Sub Initialize()
		End Sub
	End Class
End Class
' File: ComplexControl_Part2.cs
Partial Public Class ComplexControl
	Partial Public Class NestedControl
		Public Sub Cleanup()
		End Sub
	End Class
End Class

Practical Applications

Partial classes are particularly beneficial in scenarios involving automatically generated source code, such as Forms, where Visual Studio creates Windows Forms. This setup allows developers to separate UI design code in a distinct source file, enabling them to extend or modify the class without impacting the original UI design.

In web applications, partial classes facilitate the separation of generated web service wrapper code from custom business logic, ensuring that updates to web services do not overwrite custom modifications. Similarly, in applications using LINQ to SQL, dbml files generate partial class definitions that can be extended to include additional functionality or business logic without touching the auto-generated code.

// Auto-generated UI class
public partial class MainForm : Form
{
    // Designer code
}
// Custom logic for MainForm
public partial class MainForm
{
    // Custom event handlers and methods
}

// Auto-generated UI class
public partial class MainForm : Form
{
    // Designer code
}
// Custom logic for MainForm
public partial class MainForm
{
    // Custom event handlers and methods
}

' Auto-generated UI class
Partial Public Class MainForm
	Inherits Form

	' Designer code
End Class
' Custom logic for MainForm
Partial Public Class MainForm
	Inherits Form

	' Custom event handlers and methods
End Class

IronPDF: C# PDF Library

C# Partial (How It Works For Developers): Figure 1 - IronPDF

IronPDF is a comprehensive library for .NET that allows developers to create, read, and edit PDF documents in their applications. It provides a straightforward approach to generate PDFs from HTML using IronPDF, URLs, images, ASPX, and text, making it a versatile tool for reporting, document generation, and web content archiving. IronPDF excels in its ease of use, requiring minimal setup to integrate into any .NET project, including applications developed with C#.

Integrating IronPDF with Partial Classes

To illustrate the integration of IronPDF with partial classes, let's consider an example where we have a web application that generates reports in PDF format. We'll split the functionality across partial class files to keep our business logic separate from our PDF generation logic.

Setting Up IronPDF

First, ensure IronPDF is added to your project. This can typically be done via NuGet Package Manager with the command:

Install-Package IronPdf

Creating the Partial Class for Report Generation

We will divide our class into two parts: one for business logic related to report data and another for PDF generation using IronPDF.

File 1: ReportGenerator_BusinessLogic.cs

This file contains business logic for preparing the data for the report.

public partial class ReportGenerator
{
    public IEnumerable<string> GetDataForReport()
    {
        // Imagine this method fetches and prepares data for the report
        return new List<string> { "Data1", "Data2", "Data3" };
    }
}

public partial class ReportGenerator
{
    public IEnumerable<string> GetDataForReport()
    {
        // Imagine this method fetches and prepares data for the report
        return new List<string> { "Data1", "Data2", "Data3" };
    }
}

Partial Public Class ReportGenerator
	Public Function GetDataForReport() As IEnumerable(Of String)
		' Imagine this method fetches and prepares data for the report
		Return New List(Of String) From {"Data1", "Data2", "Data3"}
	End Function
End Class

File 2: ReportGenerator_PdfGeneration.cs

This file utilizes IronPDF to generate a PDF report from the prepared data.

public partial class ReportGenerator
{
    public void GeneratePdfReport()
    {
        var renderer = new IronPdf.ChromePdfRenderer();
        var data = GetDataForReport();
        var htmlContent = $"<html><body><h1>Report</h1><p>{string.Join("</p><p>", data)}</p></body></html>";
        // Generate PDF from HTML string
        var pdf = renderer.RenderHtmlAsPdf(htmlContent);
        // Save the PDF to a file
        pdf.SaveAs("Report.pdf");
        Console.WriteLine("Report generated successfully.");
    }
}

public partial class ReportGenerator
{
    public void GeneratePdfReport()
    {
        var renderer = new IronPdf.ChromePdfRenderer();
        var data = GetDataForReport();
        var htmlContent = $"<html><body><h1>Report</h1><p>{string.Join("</p><p>", data)}</p></body></html>";
        // Generate PDF from HTML string
        var pdf = renderer.RenderHtmlAsPdf(htmlContent);
        // Save the PDF to a file
        pdf.SaveAs("Report.pdf");
        Console.WriteLine("Report generated successfully.");
    }
}

Partial Public Class ReportGenerator
	Public Sub GeneratePdfReport()
		Dim renderer = New IronPdf.ChromePdfRenderer()
		Dim data = GetDataForReport()
		Dim htmlContent = $"<html><body><h1>Report</h1><p>{String.Join("</p><p>", data)}</p></body></html>"
		' Generate PDF from HTML string
		Dim pdf = renderer.RenderHtmlAsPdf(htmlContent)
		' Save the PDF to a file
		pdf.SaveAs("Report.pdf")
		Console.WriteLine("Report generated successfully.")
	End Sub
End Class

Usage

With the partial class setup, generating a PDF report becomes a matter of invoking the GeneratePdfReport method on an instance of the ReportGenerator class.

var reportGenerator = new ReportGenerator();
reportGenerator.GeneratePdfReport();

var reportGenerator = new ReportGenerator();
reportGenerator.GeneratePdfReport();

Dim reportGenerator As New ReportGenerator()
reportGenerator.GeneratePdfReport()

C# Partial (How It Works For Developers): Figure 2 - PDF Report Output

Conclusion

C# Partial (How It Works For Developers): Figure 3 - Licensing

The use of partial classes, partial methods, and nested partial types in C# provides developers with a flexible and powerful tool for code organization and management. By separating auto-generated code from business logic, user interface control definitions, and other parts of the application, developers can create more maintainable, readable, and scalable applications.

By separating the concerns of business logic and PDF processing, developers can achieve better code organization, maintainability, and scalability. IronPDF's robust features combined with the organizational benefits of partial classes create a powerful toolset for .NET developers working with PDFs in their projects. You can try IronPDF for free using its free trial on IronPDF. If you are interested in buying, the license of IronPDF starts from $749.

Chipego Kalinda

Chat with engineering team now

Software Engineer

Chipego has a natural skill for listening that helps him to comprehend customer issues, and offer intelligent solutions. He joined the Iron Software team in 2023, after studying a Bachelor of Science in Information Technology. IronPDF and IronOCR are the two products Chipego has been focusing on, but his knowledge of all products is growing daily, as he finds new ways to support customers. He enjoys how collaborative life is at Iron Software, with team members from across the company bringing their varied experience to contribute to effective, innovative solutions. When Chipego is away from his desk, he can often be found enjoying a good book or playing football.

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