Writing software is the act of creation, and Android development is no exception. It’s not just about making some work. It’s about the application that design can grow over time, adapt and remain easy to manage.
As an Android developer facing countless architectural challenges, I found that following reliable principles can transform even the most tangled code base into a clean system. These are not abstract principles, but result-oriented and reproducible methods to write powerful, scalable, and maintainable code.
This article will see how to apply it to Android development through real-world examples, practical techniques and experience from the Meta WhatsApp team.
The solid principles proposed by Robert C. Martin are five design principles for object programming, which can ensure a clean and effective software architecture.
- Single Responsibility Principle (SRP): The class should have one and only reason to change.
- Open/Close Principle (OCP): Software entities should be open for expansion, but modified.
- Liskov Alternative Principle (LSP): A subtype must be able to replace its primitive type.
- Interface isolation principle (ISP): The interface should be client-specific and does not force implementations of unused methods.
- Dependency Inversion Principle (DIP): Advanced modules should depend on abstraction, not on low-level modules.
By integrating these principles into Android development, we can create applications that are easy to scale, test, and maintain.
The single responsibility principle is the basis for writing maintainable code. It points out that every class must have a concern. A common anti-pattern is considering activity or fragmentation is some “God Classes” that start with UI rendering, then handle responsibility in terms of data acquisition, error handling, etc. This method makes testing and maintenance nightmare.
With SRP, separate different issues for different components: for example, in a news application, create or read news.
class NewsRepository {
fun fetchNews(): List {
// Handles data fetching logic
}
}
class NewsViewModel(private val newsRepository: NewsRepository) {
fun loadNews(): LiveData {
// Manages UI state and data flow
}
}
class NewsActivity : AppCompatActivity() {
// Handles only UI rendering
}
There is only one responsibility per class; therefore, it is easy to test and modify without side effects.
In modern Android development, SRP is mainly implemented with the recommended use of JetPack. For example, logic related to data manipulation logic may be located inside ViewModel, while activities or fragments should only care about UI and interaction. Data acquisition may be delegated to some separate repository, whether from a local database such as a room or network layer (such as Raterofit). This reduces the risk of the UI class, as each component has only one responsibility. At the same time, your code will be easier to test and support.
The open/closed principle declares that a class should be opened for extension, but cannot be modified. This is more reasonable for Android apps as they keep upgrading and adding new features.
The best examples of how to use OCP principles in Android applications are interfaces and abstract classes. For example:
interface PaymentMethod {
fun processPayment(amount: Double)
}
class CreditCardPayment : PaymentMethod {
override fun processPayment(amount: Double) {
// Implementation for credit card payments
}
}
class PayPalPayment : PaymentMethod {
override fun processPayment(amount: Double) {
// Implementation for PayPal payments
}
}
Adding a new payment method does not require changing the existing class; it requires creating a new class. This is where the system becomes flexible and can be scaled.
In applications created for Android devices, the open/closed principle is very useful in function switching and dynamic configuration. For example, if your application has analytics Tracker base interface that reports events as different analytics services, Firebase and Mixpanel, and a custom internal tracker, you can add each new service as a separate class without changing Existing code. This makes your analysis module open for extensions – you can add new trackers, but modify them for modification: you won’t rewrite existing classes every time you add a new service.
Liskov’s alternative principle states that subclasses should be able to replace their underlying categories and that the behavior of the application must not be changed. In Android, this principle is the basis for designing reusable and predictable components.
For example, a graphical application:
abstract class Shape {
abstract fun calculateArea(): Double
}
class Rectangle(private val width: Double, private val height: Double) : Shape() {
override fun calculateArea() = width * height
}
class Circle(private val radius: Double) : Shape() {
override fun calculateArea() = Math.PI * radius * radius
}
Both rectangle and Circle Anyone else can be replaced without system failure, which means the system is flexible and follows the LSP.
Consider Android recyclerview.Adapter Subclass. Each subclass of the adapter is from recyclerview.Adapter
In larger applications, it is often an interface that defines too much responsibility, especially around the network or data storage. Instead, break them down into smaller, more targeted interfaces. For example, the APIAUTH interface responsible for user authentication endpoints should be different from the Apiposts interface responsible for blog posts or social feed endpoints. This separation will prevent customers who only need post-related methods from being forced to rely on and implement authentication calls, thereby maintaining code as well as testing coverage for more leaner.
The principle of interface isolation means that several smaller, focused interfaces should not be used. This principle prevents the class from implementing unnecessary methods.
For example, considering a large interface that represents the user’s actions, instead considering Kotlin code:
interface Authentication {
fun login()
fun logout()
}
interface ProfileManagement {
fun updateProfile()
fun deleteAccount()
}
Classes that implement these interfaces can only focus on the required functionality, thus cleaning up the code and making it more maintainable.
The dependency inversion principle facilitates decoupling by ensuring that high-level modules depend on abstraction rather than concrete implementations. This principle is perfectly consistent with Android’s modern development practice, especially in daggers and handles such as dependency injection frames.
For example:
class UserRepository @Inject constructor(private val apiService: ApiService) {
fun fetchUserData() {
// Fetches user data from an abstraction
}
}
here, UserRepository Depends on abstraction Apiservicemaking it flexible and testable. This approach allows us to replace implementations, such as using mock services during testing.
Frameworks such as Hilt, Dagger, and Koin facilitate dependency injection by providing a way to provide dependencies to Android components, without having to directly instantiate them. For example, in the repository, you will inject an abstract example, the Apiservice interface. This way, you can easily switch network implementations instead of memory mock services for local testing and don’t need to change anything in the repository code. In real applications, you can find courses annotated with @Inject or @provides to provide these abstractions, making your application modular and test-friendly.
Adopting solid principles in Android development brings tangible benefits:
- Improve detectability: Centralized classes and interfaces make writing unit tests easier.
- Enhanced maintainability: Definite concerns simplify debugging and updates.
- Scalability: Modular design enables seamless functionality.
- cooperate: Well-structured code helps teamwork and reduces boarding time for new developers.
- Performance optimization: Lean, effective architecture minimizes unnecessary processing and memory usage.
In feature-rich applications, such as e-commerce or social networking applications, solid principles applications can greatly reduce the risk of regression every time a new feature or service is added. For example, if a new requirement requires an in-app purchase stream, a separate module could be introduced that would implement the required interface (payment, analysis) without touching the existing module. This modular approach is solid-powered, allowing your Android app to quickly adapt to market demands and prevents the code base from turning into spaghetti over time.
In a large project, many developers are required to collaborate, and it is highly recommended to keep complex code bases as reliable principles. For example, separating data acquisition, business logic and UI processing in a chat module helps reduce the chance of regression while extending the code using new features. Similarly, DIP applications are essential for abstract network operations and therefore can vary between network clients without interruption.
The Solid Principle is not only a theoretical guide, but is actually a practical idea of creating elastic, adaptable and maintainable software. In the rapidly evolving world of Android development, as demand changes almost as frequently as technology, adherence to these principles provides a firm foundation for successful building success.
Good code is not just about making something work, but creating a system that can continue to run and grow with evolving demand. By embracing solid principles, you can not only write better code, but also build the fun of development, expansion and maintenance.
