Why Use cases / Interactors in Android Kotlin? - Purpose & Use Cases

The Big Idea

Discover how use cases can untangle your app's messy logic and make coding a breeze!

The Scenario

Imagine building an app where every screen directly talks to the database and handles all the business rules itself. For example, the login screen checks user credentials, updates user status, and fetches user data all in one place.

The Problem

This approach quickly becomes messy and confusing. When you want to change how login works, you have to hunt through many screens. Bugs hide easily because logic is scattered everywhere. It's like trying to fix a tangled ball of yarn.

The Solution

Use cases or interactors act like clear instructions for each task your app does. They keep business rules in one place, separate from screens and data storage. This makes your app easier to understand, test, and change without breaking other parts.

Before vs After

✗ Before

fun loginUser(username: String, password: String) {
  if (db.checkUser(username, password)) {
    db.updateStatus(username, "online")
    val data = db.getUserData(username)
    showData(data)
  }
}

✓ After

class LoginUseCase(private val repo: UserRepository) {
  fun execute(username: String, password: String): UserData? {
    if (repo.validateUser(username, password)) {
      repo.setUserOnline(username)
      return repo.fetchUserData(username)
    }
    return null
  }
}

What It Enables

It enables building apps where business logic is clear, reusable, and easy to maintain, making your code more reliable and your development faster.

Real Life Example

Think of a shopping app where adding an item to the cart involves checking stock, applying discounts, and updating totals. A use case handles all these steps cleanly, so the cart screen just calls it without worrying about details.

Key Takeaways

Use cases keep business logic separate from UI and data layers.

They make your app easier to test and maintain.

They help avoid tangled, hard-to-change code.