Coroutines & Background Work

The problem

The main thread (also called the UI thread) draws the screen and handles taps. If you run a long task on it — a network call, a big file read — the UI freezes and Android may show “App Not Responding”. The solution is to move that work to a background thread. Coroutines make this easy and readable.

suspend functions

suspend fun loadUser(): User {
    delay(1000)            // a non-blocking pause (won't freeze the UI)
    return api.getUser(1)
}

Launching coroutines in the right scope

// in a ViewModel — cancelled automatically when the ViewModel clears
viewModelScope.launch {
    val user = loadUser()
    _name.value = user.name
}

Switching threads with Dispatchers

withContext(Dispatchers.IO) {
    // heavy work: file, network, database
}
// back on the main thread automatically after this block

Doing things in parallel

suspend fun loadDashboard() = coroutineScope {
    val user = async { api.getUser(1) }
    val posts = async { api.getPosts() }
    Pair(user.await(), posts.await())   // both run together
}

Guaranteed background jobs: WorkManager

Coroutines run while your app is alive. For work that must finish even if the app closes or the phone restarts — syncing, uploading, backups — use WorkManager.

class SyncWorker(ctx: Context, params: WorkerParameters) :
    CoroutineWorker(ctx, params) {
    override suspend fun doWork(): Result {
        return try { syncData(); Result.success() }
        catch (e: Exception) { Result.retry() }
    }
}

val work = OneTimeWorkRequestBuilder<SyncWorker>()
    .setConstraints(Constraints(requiredNetworkType = NetworkType.CONNECTED))
    .build()
WorkManager.getInstance(context).enqueue(work)

Choosing the right tool

• Short async work tied to a screen → coroutines in viewModelScope.
• Guaranteed deferred work → WorkManager.
• Ongoing user-visible task (music, navigation) → a Foreground Service.

Summary: Never block the main thread. Use coroutines for in-app async work and WorkManager for jobs that must complete reliably in the background.