Abstract Factory Pattern in C# – Real-Time Example (UI Theme System)

What is Abstract Factory Pattern?

The Abstract Factory Pattern is a creational design pattern that creates families of related objects without specifying their concrete classes.

It provides a factory of factories.

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Why Use Abstract Factory?

• Ensure related objects are used together
• Maintain consistency across components
• Avoid mixing incompatible objects
• Improve scalability and flexibility

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Real-Time Scenario

In a UI system:

• Light Theme → Light Button, Light TextBox
• Dark Theme → Dark Button, Dark TextBox

👉 All components should match the selected theme

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Implementation

Step 1: Abstract Products

public interface IButton
{
    void Render();
}

public interface ITextBox
{
    void Render();
}

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Step 2: Concrete Products (Light Theme)

public class LightButton : IButton
{
    public void Render() => Console.WriteLine("Light Button");
}

public class LightTextBox : ITextBox
{
    public void Render() => Console.WriteLine("Light TextBox");
}

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Step 3: Concrete Products (Dark Theme)

public class DarkButton : IButton
{
    public void Render() => Console.WriteLine("Dark Button");
}

public class DarkTextBox : ITextBox
{
    public void Render() => Console.WriteLine("Dark TextBox");
}

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Step 4: Abstract Factory

public interface IUIFactory
{
    IButton CreateButton();
    ITextBox CreateTextBox();
}

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Step 5: Concrete Factories

public class LightThemeFactory : IUIFactory
{
    public IButton CreateButton() => new LightButton();
    public ITextBox CreateTextBox() => new LightTextBox();
}

public class DarkThemeFactory : IUIFactory
{
    public IButton CreateButton() => new DarkButton();
    public ITextBox CreateTextBox() => new DarkTextBox();
}

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Usage Example

IUIFactory factory = new DarkThemeFactory();

var button = factory.CreateButton();
var textbox = factory.CreateTextBox();

button.Render();
textbox.Render();

Output

Dark Button
Dark TextBox

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Key Concept

Instead of:

new DarkButton();
new LightTextBox(); // ❌ mismatch

We do:

factory.CreateButton();
factory.CreateTextBox();

👉 Ensures consistency

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Advantages

• Ensures compatible object creation
• Promotes consistency
• Easy to switch entire family
• Follows Open/Closed Principle

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Disadvantages

• More interfaces and classes
• Complex structure
• Harder to implement initially

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When to Use

• When system needs multiple related object families
• When consistency between objects is required
• When switching between configurations (themes, environments)
• When object creation should be abstracted

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Real Project Mapping (.NET + Angular)

Feature	Usage
UI themes	Abstract Factory
Multi-database support	Abstract Factory
Payment providers (family)	Abstract Factory
Multi-tenant apps	Abstract Factory

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Pro Tip (Advanced .NET Usage)

• Combine with Dependency Injection for runtime switching
• Use configuration to select factory (appsettings.json)
• Useful in multi-environment systems (Dev, Prod)

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Summary

Abstract Factory Pattern helps you:

• Create related objects consistently
• Switch entire families easily
• Build scalable and maintainable systems

👉 Perfect for themes, multi-provider systems, environment-based configurations