Android Usage

    Use stores in Android apps with Kotlin.

    This page shows the recommended path first, then advanced customization APIs.

    Use generated Kotlin types with the built-in Gson serializer.

    1. Register Store Once

    Register your store during app startup (for example in Activity.onCreate when savedInstanceState == null):

    import com.callstack.brownie.registerStoreIfNeeded
import com.callstack.rnapp.brownfieldlib.BrownfieldStore
import com.callstack.rnapp.brownfieldlib.User

registerStoreIfNeeded(
  storeName = BrownfieldStore.STORE_NAME
) {
  BrownfieldStore(
    counter = 0.0,
    user = User(name = "Username")
  )
}

    registerStoreIfNeeded returns null when the same key is already registered, which keeps registration idempotent across lifecycle re-entries.

    2. Retrieve the Typed Store

    import com.callstack.brownie.Store
import com.callstack.brownie.StoreManager
import com.callstack.brownie.store
import com.callstack.rnapp.brownfieldlib.BrownfieldStore

val store: Store<BrownfieldStore>? = StoreManager.shared.store(BrownfieldStore.STORE_NAME)

    3. Read, Update, and Subscribe

    // Read current state
val current = store?.state

// Update whole state with copy()
store?.set { state ->
  state.copy(counter = state.counter + 1)
}

// Subscribe to full state changes
val unsubscribe = store?.subscribe { newState ->
  println("Counter: ${newState.counter}")
}

// Subscribe to a selected slice only
val unsubscribeCounter = store?.subscribe(
  selector = { state -> state.counter.toInt() },
  onChange = { counter -> println("Counter: $counter") }
)

// Cleanup subscription
unsubscribe?.invoke()
unsubscribeCounter?.invoke()

    Advanced Path (Custom Serialization)

    Use this when default Gson serialization is not enough (custom formats, compatibility rules, encrypted payloads, etc.).

    Option A: Custom Serializer Interface

    import com.callstack.brownie.BrownieStoreSerializer
import com.callstack.brownie.brownieStoreDefinition
import com.callstack.brownie.register

data class SessionState(val token: String, val expiresAt: Long)

object SessionSerializer : BrownieStoreSerializer<SessionState> {
  override fun encode(state: SessionState): String {
    // Replace with your own format
    return """{"token":"${state.token}","expiresAt":${state.expiresAt}}"""
  }

  override fun decode(snapshotJson: String): SessionState {
    // Replace with your own parser
    TODO("Decode snapshotJson into SessionState")
  }
}

val sessionStore = brownieStoreDefinition(
  storeName = "SessionStore",
  serializer = SessionSerializer
).register(
  initialState = SessionState(token = "", expiresAt = 0L)
)

    Option B: Encode/Decode Lambdas

    import com.callstack.brownie.brownieStoreDefinition
import com.callstack.brownie.register

data class SessionState(val token: String, val expiresAt: Long)

val sessionStore = brownieStoreDefinition(
  storeName = "SessionStore",
  encode = { state ->
    """{"token":"${state.token}","expiresAt":${state.expiresAt}}"""
  },
  decode = { snapshotJson ->
    // Replace with your own parser
    TODO("Decode snapshotJson into SessionState")
  }
).register(
  initialState = SessionState(token = "", expiresAt = 0L)
)

    Both advanced options produce the same Store<State> API as the easy path.

    API Summary

    • registerStoreIfNeeded(storeName, initialState) - Easy one-time registration.
    • registerStore(storeName, initialState) - Always creates/registers store.
    • brownieStoreDefinition(...) - Store definition API (default or custom serializer).
    • StoreManager.shared.store<T>(key) - Retrieve typed store by key.
    • Store.set { ... } - Update full typed state.
    • Store.subscribe { ... } and selector subscribe(...) - Observe state changes.

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