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Building Robust Android Apps with SOLID Principles : A Comprehensive Guide

Indus Appstore Editor|3 min read|21 February 2024

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In the dynamic realm of Android app development, maintaining code that is not only functional but also scalable and easy to maintain is crucial. SOLID principles offer a set of guidelines to achieve these goals. In this article, we will delve into each SOLID principle, briefly explaining them, discussing their pros and cons, and providing a practical use case along with sample Kotlin code snippets.

1. Single Responsibility Principle (SRP):

Brief Explanation: Each class should have only one reason to change, i.e., one responsibility.


  • Maintainability: Easier to understand and maintain code.
  • Testability: Improved testability with isolated responsibilities.


  • Increased Complexity: May lead to a larger number of classes.

Use Case: A weather app with separate classes for data retrieval, parsing, and UI presentation.

Sample Code (Kotlin):

kotlinCopy codeclass WeatherDataRetriever {
    // Data retrieval logic

class WeatherDataParser {
    // Data parsing logic

class WeatherUIController {
    // UI presentation logic

2. Open-Closed Principle (OCP):

Brief Explanation: Software entities should be open for extension but closed for modification.


  • Scalability: Easier to extend functionality without modifying existing code.
  • Maintainability: Existing code remains stable during updates.


  • Learning Curve: May require a mindset shift.

Use Case: A messaging app where new message types can be added without modifying existing message handling code.

Sample Code (Kotlin):

kotlinCopy codeinterface MessageHandler {
    fun handleMessage(message: Message)

class TextMessageHandler : MessageHandler {
    // Handle text messages

class ImageMessageHandler : MessageHandler {
    // Handle image messages

3. Liskov Substitution Principle (LSP):

Brief Explanation: Subtypes must be substitutable for their base types without altering the correctness of the program.


  • Polymorphism: Subtypes can be used interchangeably.
  • Consistency: Ensures consistent behavior in derived classes.


  • Complexity: Ensuring adherence can be challenging, especially in large codebases.

Use Case: A file management app ensuring that each file type (text, image, video) behaves consistently when processed.

Sample Code (Kotlin):

kotlinCopy codeopen class File {
    // Common file properties and methods

class TextFile : File {
    // Additional methods specific to text files

class ImageFile : File {
    // Additional methods specific to image files

4. Interface Segregation Principle (ISP):

Brief Explanation: Clients should not be forced to implement interfaces they do not use.


  • Flexibility: Clients only implement interfaces relevant to them.
  • Maintenance: Changes to one interface do not affect others.


  • Interface Proliferation: May lead to a larger number of small interfaces.

Use Case: In a payment processing app, segregating interfaces for different payment methods.

Sample Code (Kotlin):

kotlinCopy codeinterface CreditCardPayment {
    fun processCreditCardPayment()

interface PayPalPayment {
    fun processPayPalPayment()

class CreditCardPaymentProcessor : CreditCardPayment {
    // Implement credit card payment logic

class PayPalPaymentProcessor : PayPalPayment {
    // Implement PayPal payment logic

5. Dependency Inversion Principle (DIP):

Brief Explanation: High-level modules should not depend on low-level modules; both should depend on abstractions.


  • Decoupling: High-level modules are not directly dependent on low-level modules.
  • Testability: Easier unit testing with mock objects.


  • Learning Curve: Implementing dependency injection can be challenging initially.

Use Case: In a weather app, decoupling the user interface from the data retrieval and storage modules.

Sample Code (Kotlin):

kotlinCopy codeinterface WeatherDataProvider {
    fun getWeatherData(): WeatherData

class WeatherDataRetriever(private val dataProvider: WeatherDataProvider) {
    fun fetchWeather() {
        val data = dataProvider.getWeatherData()
        // Process and display weather data

Adhering to SOLID principles in Android development using Kotlin provides a foundation for creating robust, scalable, and maintainable applications. While challenges exist, the benefits far outweigh the drawbacks, enabling developers to build high-quality Android apps that stand the test of time.


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