Applying S.O.L.I.D. Principles to Flutter Development
SOLID Principles for Maintainable, Scalable, and Flexible Flutter Development
SOLID principles are a set of object-oriented design principles that help developers create maintainable, scalable, and flexible software. They are a Clean Code standard and one of the main principles and popular interview questions asked in technical interviews.
SOLID principles are an acronym for the following five principles:
- Single Responsibility Principle (SRP): A class should have only one responsibility. This can be applied to functions also as - Each function should do only one thing.
- Open/Closed Principle (OCP): Classes should be open for extension but closed for modification.
- Liskov Substitution Principle (LSP): Subclasses should be substitutable for their parent classes.
- Interface Segregation Principle (ISP): Interfaces should be segregated into smaller, more specific interfaces.
- Dependency Inversion Principle (DIP): High-level modules should not depend on low-level modules. Both should depend on abstractions.
These principles can be applied to Flutter development in a number of ways — let's see it further in the text!
Benefits of using SOLID principles in Flutter development:
- Easier to maintain code: SOLID principles can help you create code that is easier to understand and maintain. This is because SOLID principles encourage you to write code that is modular, well-organized, and loosely coupled.
- More flexible code: SOLID principles can help you create code that is more flexible and adaptable to change. This is because SOLID principles encourage you to write code that is open for extension but closed for modification.
- More scalable code: SOLID principles can help you create code that is more scalable and can handle more users and data. This is because SOLID principles encourage you to write code that is loosely coupled and does not rely on any specific implementation details.
- Adaptability to changing requirements: SOLID principles can help you create code that is more adaptable to changing requirements. This is because SOLID principles encourage you to write code that is modular and loosely coupled. This makes it easier to add new features or modify existing features without breaking the rest of your code.
Why are SOLID principles so important?!
While computing has changed a lot in the last 20 years since the SOLID principles were established, they are still the best practices for designing software. Applying the SOLID principles increases the overall development lifecycle speed and efficiency and makes you a top-notch developer!
How to apply SOLID principles to Flutter development:
1. SRP (Single Responsibility Principle): Create focused widgets for user input and data display.
In Flutter, SRP can be applied to classes and widgets. For example, consider a User class that is responsible for managing user data. It should only handle user-related operations and not be responsible for rendering UI.
class User {
String name;
String email;
void saveUserData() {
// Save user data to a database
}
void loadUserData() {
// Load user data from a database
}
}2. Open/Closed Principle (OCP)- Use abstract classes and interfaces to allow for extension without modification:
In Flutter, we can achieve OCP by using inheritance and polymorphism. Let’s say we have a base Shape class with a method calculateArea(). We want to extend this class with different shapes without modifying the base class. This means that we should be able to add new features or behaviors to a class without changing its existing code. This helps to maintain the existing code and avoid introducing new bugs.
abstract class Shape {
double calculateArea();
}
class Circle extends Shape {
double radius;
@override
double calculateArea() {
return 3.14 * radius * radius;
}
}
class Rectangle extends Shape {
double length;
double width;
@override
double calculateArea() {
return length * width;
}
}3. Liskov Substitution Principle (LSP) — Base classes must be able to use objects of derived classes without knowing it. The LSP states that subtypes should be substitutable for their base types:
In Flutter, this principle is crucial for maintaining UI consistency. Create interfaces for specific tasks and implement those interfaces in your classes.
abstract class Animal {
String label;
String speak();
}
class Dog extends Animal {
@override
String speak() => 'Woof';
}
class Cat extends Animal {
@override
String speak() => 'Meow';
}
class App {
void run() {
final animals = [Dog(), Cat()];
animals.forEach((animal) => print('${animal.label} says ${animal.speak()}'));
}
}4. Interface Segregation Principle (ISP) — classes should not be forced to depend on interfaces they don’t use:
The ISP states that clients should not be forced to depend on interfaces they don’t use. This means that we should break down large interfaces into smaller, more specialized ones so that clients only need to implement the methods they actually use.
In Flutter, this can be applied to abstract classes or interfaces. For example, consider a Logger class that has methods for both logging to a file and sending logs to a server. These functionalities can be segregated into two interfaces.
abstract class FileLogger {
void logToFile(String message);
}
abstract class ServerLogger {
void logToServer(String message);
}
class Logger implements FileLogger, ServerLogger {
@override
void logToFile(String message) {
// Logic to log to a file
}
@override
void logToServer(String message) {
// Logic to send logs to a server
}
}5. Dependency Inversion Principle (DIP)- Use dependency injection to inject dependencies into your classes, for example GetIt:
In Flutter, DIP can be implemented using dependency injection. Consider a UserService that depends on a UserRepository for data operations. Instead of directly instantiating UserRepository, it should be injected into UserService.
class UserRepository {
Future<List<User>> getUsers() async {
// Logic to get users from a data source
}
}
class UserService {
final UserRepository userRepository;
UserService(this.userRepository);
Future<List<User>> getAllUsers() async {
return userRepository.getUsers();
}
}Google explained very nicely DIP and why it’s beneficial for the flexible, following clean code codebase, here.
These examples demonstrate how the SOLID principles can be applied in Flutter to write more maintainable, modular, and flexible code but can be applied in all Object Oriented programming languages. Personally, I used them in Java, Kotlin, and Dart so far.
