使い方
- インストールコマンドをコピーし、自分の環境へ導入する前にソースを確認します。
- 必要なツール、認証情報、対応環境を原文で確認します。
- 入力と成果物を指定し、出力を資料と照合します。
npx skills add https://github.com/rcosteira79/android-skills --skill datastore開始前の確認
- 導入にはモデル契約、API枠、ファイルへのアクセス許可は含まれません。
- スター数や導入数は活動の指標であり、独立した品質・安全性試験ではありません。
見出し、例、コード、表、リンク、参照画像を含む原文を表示しています。
Jetpack DataStore for Android and KMP
Reactive coroutine-based key-value / typed storage; the same androidx.datastore:datastore-preferences-core runs on Android, iOS, and JVM — only the file-path producer is platform-specific. (Web support is 1.3.0-alpha only, and it's sessionStorage/OPFS-backed there, not file-path-based.) This reference covers the storage-choice call plus the two error/path traps, not the basics of Preferences keys, edit { }, or Serializer<T>. Adapted from Meet-Miyani/compose-skill; MIT. Related: android-skills:android-data-layer, android-skills:kmp-boundaries, android-skills:kotlin-flows.
Preferences vs Typed vs Room
| Need | Storage |
|---|---|
| Key-value flags (theme, locale, onboarding done) | Preferences DataStore |
| One typed object, many related fields, schema evolution | Typed DataStore + Serializer<T> |
Relational data, indexes, WHERE / JOIN, >100 entries, paging | Room |
| Payloads above ~50KB per write | Room / filesystem — DataStore rewrites the whole file on every edit |
Rule of thumb: if a WHERE clause would be useful, use Room.
The two traps
`.catch` must match `IOException` specifically — never a broad `catch`. A bare catch { emit(emptyPreferences()) } swallows CancellationException (breaking structured concurrency) and hides serializer/corruption errors behind a silent empty state.
val settings: Flow<UserSettings> = dataStore.data
.catch { e -> if (e is IOException) emit(emptyPreferences()) else throw e }
.map { p -> UserSettings(p[Keys.DARK_MODE] ?: false, p[Keys.LOCALE] ?: "en") }Typed-DataStore corruption recovery triggers on `CorruptionException`, NOT `IOException`. The serializer's readFrom must wrap parse failures in CorruptionException, and the store needs a ReplaceFileCorruptionHandler — without it, one corrupt file makes every read fail permanently.
object AppSettingsSerializer : Serializer<AppSettings> {
override val defaultValue = AppSettings()
override suspend fun readFrom(input: InputStream): AppSettings =
try { Json.decodeFromString(input.readBytes().decodeToString()) }
catch (e: SerializationException) { throw CorruptionException("Cannot read AppSettings", e) }
override suspend fun writeTo(t: AppSettings, output: OutputStream) =
output.write(Json.encodeToString(t).encodeToByteArray())
}
val store = DataStoreFactory.create(
serializer = AppSettingsSerializer,
corruptionHandler = ReplaceFileCorruptionHandler { AppSettings() },
produceFile = { File(context.filesDir, "app_settings.json") },
)KMP factory — per-platform path (not the temp dir)
// commonMain
fun createPreferencesDataStore(producePath: () -> String): DataStore<Preferences> =
PreferenceDataStoreFactory.createWithPath(produceFile = { producePath().toPath() })
// android: context.filesDir.resolve(PREFS_FILE).absolutePath
// ios: NSDocumentDirectory via NSFileManager
// jvm: File(System.getProperty("user.home"), ".myapp") — NOT java.io.tmpdir (the OS may wipe it on reboot)(In a composable, never runBlocking on DataStore — it parks the main thread on disk I/O, risking an ANR, and re-runs every recomposition. Expose a StateFlow and collect with collectAsStateWithLifecycle.)
