Taking a Look at the UseCase Pattern in Kotlin

The UseCase pattern is a popular architectural pattern used in Kotlin for developing robust and maintainable Android applications. It helps separate business logic from the user interface, making code more testable, reusable, and easier to understand. In this article, we'll take a closer look at the UseCase pattern and show you some examples of how it can be implemented in Kotlin.

What is the UseCase Pattern?

The UseCase pattern is based on the principle of breaking down an application's functionality into discrete use cases or actions. Each use case represents a specific task or operation that the application needs to perform. By encapsulating these use cases within dedicated classes, we can keep our codebase modular and focused on single responsibilities.

Benefits of the UseCase Pattern

Implementing the UseCase pattern offers several benefits:

1. Separation of Concerns: By isolating business logic in dedicated UseCase classes, we achieve a clear separation between the UI layer and the underlying data or domain layer.
2. Single Responsibility Principle (SRP): Each UseCase class focuses on a single task, adhering to the SRP and keeping the codebase more maintainable.
3. Testability: Since UseCase classes are independent of the UI framework, they can be easily tested without the need for complex setup or mocking.
4. Reusability: UseCase classes can be reused across different parts of the application, reducing code duplication and promoting code sharing.

Implementing the UseCase Pattern

To illustrate the UseCase pattern, let's consider an example of a note-taking application. We'll implement a CreateNoteUseCase that handles the logic for creating new notes.

First, we define an interface for our UseCase:

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1interface CreateNoteUseCase {
2    fun execute(title: String, content: String)
3}

Next, we create a concrete implementation of this UseCase:

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1class CreateNoteUseCaseImpl(private val noteRepository: NoteRepository) : CreateNoteUseCase {
2
3    override fun execute(title: String, content: String) {
4        val newNote = NoteEntity(title, content)
5        noteRepository.save(newNote)
6    }
7}

In this example, the CreateNoteUseCaseImpl class receives a NoteRepository dependency through its constructor. The repository abstraction allows us to decouple the UseCase from specific data storage implementations, such as a local database or network service.

Finally, we can invoke the CreateNoteUseCase in our user interface layer:

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1class CreateNoteActivity : AppCompatActivity() {
2    private val createNoteUseCase: CreateNoteUseCase = // Initialize the UseCase
3
4    // ...
5
6    private fun onSaveNoteClicked() {
7        val title = editTextTitle.text.toString()
8        val content = editTextContent.text.toString()
9        createNoteUseCase.execute(title, content)
10    }
11}

By following this pattern, we keep our UI layer focused on handling user interactions while delegating complex business logic to dedicated UseCase classes.

The UseCase pattern is a valuable tool for structuring and organizing your Kotlin-based Android applications. By separating concerns, adhering to the SRP, and promoting testability and reusability, you can develop more maintainable and scalable codebases.