Flutter Made Simple: Applying SOLID Principles

Discover the simplicity behind building better Flutter apps. Uncover the magic of SOLID principles and learn how they can make your code cleaner and more maintainable. 

This guide provides easy-to-follow tips for integrating SOLID principles into your Flutter projects, ensuring your app development journey is both smooth and efficient.

SOLID Principles

Principle Explanation
Single Responsibility Principle (SRP) A class should have only one reason to change.
Open/Closed Principle (OCP) A class should be open for extension but closed for modification.
Liskov Substitution Principle (LSP) Objects of a superclass should be able to replace objects of the subclass without affecting correctness.
Interface Segregation Principle (ISP) A class should not be forced to implement interfaces it does not use.
Dependency Inversion Principle (DIP) High-level modules should not depend on low-level modules. Both should depend on abstractions.

Single Responsibility Principle (SRP)

A solid principle begins with an “S”: the SINGLE RESPONSIBILITY PRINCIPLE.

A class should have only one reason to change, and it should encapsulate only one responsibility or job within a software system. 

This principle promotes 

* clarity, 

* collaboration and parallel development,

* testability,

* reduced code coupling,

* maintainability, and 

*flexibility by ensuring that each class has a well-defined purpose and that changes to one aspect of the system do not affect unrelated aspects encapsulated within the same class.

Open/Closed Principle (OCP)

In addition, there is a second big principle that starts with an “O” called the OPEN-CLOSED PRINCIPLE. 

This principle says that every class and method should be open for extension, but closed for modification.

In summary, the Open/Closed Principle encourages a design approach that supports 

* future changes and enhancements without modifying existing code, 

* contributing to a more maintainable, 

* scalable, and

* adaptable software system.

Liskov Substitution Principle (LSP) 
The third big principle that starts with an “L” is LISKOV SUBSTITUTION PRINCIPLE

Subtypes must be substitutable for their base types without altering the correctness of the program

According to the LSP, subclasses should be replaced with superclasses without changing the logical correctness of the program. 

Essentially, a subtype must guarantee the “usage conditions” of its super-type along with some additional behaviours.

LSP states that an object of a child class must be able to replace an object of the parent class without breaking the application.

Interface Segregation Principle (ISP)
So this brings us to our fourth principle, the fourth big principle that starts with an “I” is INTERFACE SEGREGATION PRINCIPLE

According to this principle, clients don’t need to implement behaviors they don’t want. As a general rule, you should create small interfaces with few methods.

It is better to have multiple smaller interfaces than larger interfaces.

Dependency Inversion Principle (DIP)

Lastly, the last principle that is very important in software engineering, which starts with a “D”, is the DEPENDENCY INVERSION PRINCIPLE, which states that high-level modules must not depend on low-level modules without an abstraction.

It states that high-level modules (which contain the main business logic) should not depend on low-level modules (which implement details), but both should depend on abstractions

Additionally, abstractions should not depend on details; details should depend on abstractions. 

This principle encourages the use of interfaces or abstract classes to create a level of indirection

* allowing for flexibility, 

* extensibility, 

* ease of testing, and 

* easier maintenance in a software system.



You should know: Other principle


DRY stands for Don't Repeat Yourself. It's a software development principle that emphasizes writing code such that functionality is not duplicated. 

Repeating code can make it difficult to maintain and update, as changes need to be made in multiple places.

Here are some key benefits of adhering to the DRY principle:
  • Increased maintainability
  • Reduced code size
  • Improved code quality


KISS, which stands for Keep It Simple, Stupid, is a fundamental principle in software development and other fields. 

It emphasizes the importance of simplicity and clarity in design.

The KISS principle encourages developers to create code that is:

  • Easy to understand
  • Easy to maintain
  • Easy to extend
  • Efficient


YAGNI stands for "You Ain't Gonna Need It". 

It's a principle in software development that emphasizes deferring the implementation of features until they are actually needed. 

This helps to avoid wasting time and effort on functionality that may never be used, and it keeps the code base lean and focused.

Here are some key benefits of following the YAGNI principle:
  • Reduced development time
  • Improved code quality
  • Increased flexibility and adaptability
  • Reduced risk of technical debt