Recipe: Run a one-shot suspend action from an event

Problem: a button tap needs to call a suspend function (save, send, toggle, etc.), but a presenter’s present() isn’t a coroutine and you must not block it.

Launch from a rememberCoroutineScope() in the event handler:

@Composable
override fun present(): ComposerState {
  val scope = rememberCoroutineScope()
  var sending by rememberRetained { mutableStateOf(false) }

  return ComposerState(isSending = sending) { event ->
    when (event) {
      is ComposerEvent.Send ->
        scope.launch {
          sending = true
          messageRepository.send(event.text)
          sending = false
        }
    }
  }
}

The catch: this scope dies with the composition

rememberCoroutineScope() is tied to the presenter’s place in composition. It’s cancelled the moment the presenter leaves composition: a configuration change, the screen being popped, or navigating away. That’s fine for short, UI-tied work that can be abandoned if the user leaves.

Do not use it for work that must finish regardless of the UI:

// 🚫 If the user navigates away mid-upload, this is cancelled!
scope.launch { fileRepository.upload(hugeFile) }

Push fire-and-forget or must-complete work into the data layer, scoped to something that outlives the screen:

// ✅ The repository owns a longer-lived scope; the presenter just triggers it.
is ComposerEvent.Send -> uploadManager.enqueue(event.file)

Rule of thumb: if the result still matters after the user leaves the screen, it doesn’t belong on rememberCoroutineScope().

See also: Pull to refresh · Presenter