statedatastore

A snapshot state wrapper around the Jetpack Datastore library.

This is a highly experimental, proof-of-concept library. It’s meant to be a rough example sketch of how you could use Compose’s snapshot state system to implement automatic persistence. For more information, see my talk Opening the shutter on snapshots (slides).

Usage

Easily consume and update Preferences state via MutableStates:

val prefKey = stringPreferencesKey("pref") 

@Composable fun Screen(dataStore: StateDataStore) {
  var pref by dataStore.collectAsState(prefKey)
  TextField(pref, onValueChanged = { pref = it })
}

The pref state will automatically update whenever the backing DataStore is changed, and changes made to the pref value will automatically be written to the DataStore.

If you want to provide a default, you do that too:

var pref by dataStore.collectOrDefaultAsState(prefKey) { "default" }

There are also versions of both of these methods that you can use outside of composition:

dataStore.getAsState(prefKey)
dataStore.getOrDefaultAsState(prefKey) { "default" }

To create a StateDataStore, take a DataStore instance and call asDataStoreIn on it:

class ViewModel(dataStore: DataStore) {
  val dataStore: StateDataStore = dataStore.asDataStoreIn(coroutineScope)
}

asDataStoreIn needs a CoroutineScope to run in to observe changes and write state changes back to the DataStore.

GitHub

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