SRP Demo – SwiftUI (Single Responsibility Principle)

Overview

This project demonstrates the Single Responsibility Principle (SRP) using a SwiftUI + MVVM architecture.

Each layer in the app has one clearly defined responsibility, making the codebase easy to understand, test, and extend.

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What is SRP?

Single Responsibility Principle states:

A class or module should have only one reason to change.

In this demo:

• Views only handle UI
• ViewModels only handle presentation logic
• Repositories only handle data fetching
• Networking only handles HTTP communication
• Models only represent data

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Project Structure

SRPDemo/
│
├── APIServices/
│   └── UserRepository.swift
│
├── Model/
│   └── User.swift
│
├── Networking/
│   └── Networking.swift
│
├── Screens/
│   └── UserScreenView.swift
│
├── ViewModel/
│   └── UserViewModel.swift
│
├── ContentView.swift
└── SRPDemoApp.swift

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Responsibility Breakdown (SRP in Action)

1. Model Layer

File: User.swift

Responsibility:

• Represents user data structure
• No business logic

struct User: Codable {
    let id: Int
    let name, username, email: String
}

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2. Networking Layer

File: Networking.swift

Responsibility:

• Executes HTTP requests
• Handles networking errors
• Does NOT decode models

Key Components:

• HttpClientProtocol
• HttpClient
• NetworkError

This allows easy mocking and testing.

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3. Repository Layer

File: UserRepository.swift

Responsibility:

• Fetches user data
• Decodes API response into User
• Depends on HttpClientProtocol, not concrete implementation

Why SRP-compliant?

• Networking logic is NOT mixed here
• Decoding responsibility stays focused

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4. ViewModel Layer

File: UserViewModel.swift

Responsibility:

• Acts as a bridge between View and Repository
• Holds UI state (user, message)
• Calls repository to load data

No UI rendering or network code here.

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5. View Layer (UI)

File: UserScreenView.swift

Responsibility:

• Displays UI using SwiftUI
• Observes ViewModel state
• Triggers data load

.task {
    await viewModel.loadData()
}

The View never knows how data is fetched.

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Why This Design is SRP-Friendly

Layer	Responsibility
View	UI rendering
ViewModel	Presentation logic
Repository	Data fetching
Networking	HTTP communication
Model	Data representation

Each component has one reason to change.

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Benefits

• Clean architecture
• Easy unit testing
• Mockable dependencies
• Scalable for larger apps
• Interview‑ready MVVM + SRP example

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How to Run

1. Open SRPDemo.xcodeproj
2. Select iOS Simulator
3. Run the app

The screen fetches and displays a user from:

https://jsonplaceholder.typicode.com/users/1

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Key Takeaways

• SRP reduces tight coupling
• MVVM complements SRP well
• Protocols help enforce responsibilities

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Author

Viswa Bharath Dakka

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