Why Sealed classes in Android Kotlin? - Purpose & Use Cases

The Big Idea

Discover how sealed classes can save you from tricky bugs by making your code smarter and safer!

The Scenario

Imagine you are building an app that handles different types of user actions like clicking a button, swiping, or typing. You try to manage all these actions using simple classes or enums, but it quickly becomes confusing to keep track of all possible cases.

The Problem

Using plain classes or enums means you might forget to handle some action types, leading to bugs. Also, your code becomes cluttered with many if-else or when statements that are hard to read and maintain.

The Solution

Sealed classes let you define a fixed set of subclasses in one place. This way, the compiler knows all possible types, helping you write safer and cleaner code. It forces you to handle every case explicitly, reducing errors.

Before vs After

✗ Before

abstract class Action
class Click : Action()
class Swipe : Action()
// But you might miss handling some types in when

✓ After

sealed class Action {
  class Click : Action()
  class Swipe : Action()
}
// when covers all cases, compiler checks

What It Enables

Sealed classes enable you to write clear, safe, and maintainable code by knowing all possible types upfront.

Real Life Example

In a chat app, sealed classes can represent message states like Sent, Received, or Failed, ensuring your UI handles each state properly without missing any.

Key Takeaways

Sealed classes define a closed set of subclasses.

They help the compiler check all cases are handled.

This leads to safer and cleaner code.