Here is a line you have written a hundred times:
val state by viewModel.data.collectAsState()
It looks harmless. It is the standard way to turn a Flow into Compose state. And on a screen with live data, it quietly keeps working long after the user has walked away.
The screen nobody is watching
collectAsState starts collecting the flow and stops only when the composable leaves the composition. That sounds right until you remember what backgrounding an app does, which is almost nothing to the composition. Send the app to the background and the composable is still composed. So the collection keeps running. The flow keeps emitting. Your ViewModel keeps fetching, computing, and pushing new state to a screen that is not on screen.
On a live price ticker or a location feed, that is real battery and mobile data spent in the dark. It is also a quiet source of bugs, because off-screen updates can pile up and then hit the user with a jump of stale changes the moment they return.
The one-word fix
val state by viewModel.data.collectAsStateWithLifecycle()
collectAsStateWithLifecycle ties the collection to the lifecycle owner. When the lifecycle drops below STARTED, it stops collecting. When it comes back, it resumes. If your upstream is a stateIn or shareIn flow with WhileSubscribed, the whole pipeline can now go cold while hidden and warm back up on return. Nobody pays for a screen that is not visible.
It lives in androidx.lifecycle.runtime.compose. Add the dependency, change the one call, and the leak is gone.
Make it the default
Treat collectAsStateWithLifecycle as the default and plain collectAsState as the exception. The rare time you actually want collection to continue while the screen is hidden should be a deliberate, commented decision, not something you got by reaching for the shorter name out of habit.
The takeaway
Lifecycle awareness is not a nice-to-have you bolt on later. It is the line between work that stops when the user leaves and work that runs forever in the background. The Recomposer does not mind an empty room. It will happily keep redrawing it. Your job is to turn the lights off when everyone goes home.
🌀 Iteration 6 of **The Loopdown. field notes from an engineer who writes.
Series: **Ghosts In The Recomposition* · Featuring: The Recomposer*
← Previously in this series: Your LazyColumn recomposes on every scroll
📚 The full series: Ghosts In The Recomposition
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