Skip to content
Kaito Snezhko
Sign in

Android with Kotlin: Compose, MVVM, coroutines

How a modern Android app is structured — Jetpack Compose UI, a ViewModel holding state, coroutines, Room + Retrofit for offline-first data and navigation — from the todo, recipe and Linto apps I built.

updated 15 Jun 2026 · level beginner · 1 min read

#android#kotlin#mvvm#coroutines#room

From Interactive Mobile Applications (FH JOANNEUM, summer 2026). The exercises were a scaffold app, a todo app, a recipe app and coroutines. The final project was the Android app for Linto, our startup-project idea.

MVVM in one picture

UI (Composables)  ──events──▶  ViewModel  ──▶  Repository / data
       ▲                          │
       └──────── state (StateFlow) ┘
  • The UI only shows state and sends events. It holds no business logic.
  • The ViewModel survives screen rotation and exposes StateFlow / State.
  • The repository hides where the data comes from (memory, database, network).
kotlin
class TodoViewModel : ViewModel() {
    private val _todos = MutableStateFlow<List<Todo>>(emptyList())
    val todos = _todos.asStateFlow()

    fun add(title: String) = _todos.update { it + Todo(title) }
}

Coroutines

  • viewModelScope.launch { … } is cancelled automatically when the ViewModel is gone.
  • Do slow work on Dispatchers.IO, and only update the UI from the main thread.
  • suspend functions pause without blocking a thread.

Offline-first: Room + Retrofit

In the Linto demo app (Japanese vocabulary) the data comes from a web service, but the app also works offline:

  • Retrofit loads the vocabulary as JSON (kotlinx.serialization DTOs).
  • Room (entity, DAO, database) stores it locally, and the UI only observes the database as a Flow.
  • The repository fetches from the network, writes to Room, and if the network fails, the cached data is still shown.

A NavHost with routes; pass IDs between screens, not whole objects, and load the data again on the target screen.

Kotlin features I used a lot

Data classes, null safety (?., ?:), collection lambdas (filter, map, groupBy) and when expressions.