Android Jetpack supports KMP

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Enabling KMP Success: The Android Jetpack Journey Sungyong An KotlinConf’24 South Korea

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Sungyong An NAVER WEBTOON Android GDE @fornewid

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য়ט ߊ಴ח. KotlinConf ’24 ࣁ࣌ ղਊਸ ׮ܛפ׮. Link: h tt ps://kotlinconf.com/talks/623652/

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Kotlin Multiplatform & Jetpack KMP Android iOS Web Windows ... “Libraries and tools to write better Android apps with ease” Link: h tt ps://developer.android.com/jetpack

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Jetpack KMP ...? ? 🤔

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What makes Android successful? A thriving ecosystem: • Create apps that delight users • Businesses that are profitable • Professionals with successful careers KMP's impact: • Smooth native interoperability • Reduced time to market • Transferable skills

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KMPify everything? • Jetpack has ~800 modules 😅 • Not every library needs KMP • Each platform adds significant infra load

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History of Jetpack KMP 2020 2021 2022 2023 2024 Alpha releases d.android.com Official KMP support 🎉 🎉 Dev Libraries First product review Experiments with Workspace

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Libraries • Ready today: • Annotations, Collections, DataStore • Commonified: • Lifecycle, ViewModel, Paging • And then, the most requested... Link: h tt ps://developer.android.com/kotlin/multipla tf orm

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Making “Room” for KMP Success

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Room is a Jetpack library that makes it easier to use SQLite databases in applications, by using its annotation APIs that generate code. Link: h tt ps://developer.android.com/training/data-storage/room

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Entity @Entity data class Song ( @PrimaryKey val songId: Long, val title: String ) @Entity data class Album ( @PrimaryKey val albumId: Long ) @Entity data class Artist ( @PrimaryKey val artistId: Long )

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Data Access Object “DAO” @Dao interface MusicDao { @Insert suspend fun insertSong(song: Song) @Query("SELECT * FROM Song ORDER BY title ASC") fun getAllSongs(): Flow> }

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Database @Database( entities = [ Song::class, Album::class, Artist::class ], version = 1 ) abstract class MusicDatabase : RoomDatabase() { abstract fun musicDao(): MusicDao } @Entity data class Song( @PrimaryKey val songId: Long, ) @Entity data class Album( @PrimaryKey val albumId: Long ) @Entity data class Artist( @PrimaryKey val artistId: Long )

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KMP Support Room now supports: • Android • JVM Desktop • Native (iOS, Mac and Linux) Link: h tt ps://developer.android.com/kotlin/multipla tf orm/room

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Android KMP ? 🤔

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KMP Android ? 😱

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Room’s Migration Journey Room KMP! Kotlin Symbol Processing (KSP) Support Migrate Runtime JPL -> Kotlin Support Kotlin Codegen Add cross-platform SQLite support Migrate to SQLite drivers Cross-platform codegen

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Tooling for Success: XProcessing, XPoet & XProcessingTesting

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XProcessing Abstraction over Java Annotation Processing (JavaAP) and Kotlin Symbol Processing (KSP) Has APIs to represent: • XType <- JavaAP’s TypeMirror or KSP’s KSType • XTypeElement <- JavaAP’s TypeElement or KSP’s KSClassDeclaration • XMethodElement <- JavaAP’s ExecutableElement or KSP’s KSFunctionDeclaration … and more! Link: h tt ps://cs.android.com/androidx/pla tf orm/frameworks/suppo rt /+/.../room-compiler-processing/

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Database Declaration abstract class MusicDatabase XTypeElement

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Database Declaration abstract class MusicDatabase : RoomDatabase() { abstract fun musicDao(): MusicDao } XExecutableElement

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Database Declaration @Database( entities = [ Song::class, Album::class, Artist::class, ], version = 1 ) abstract class MusicDatabase : RoomDatabase() { abstract fun musicDao(): MusicDao } XType

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Database Declaration @Database( entities = [ Song::class, Album::class, Artist::class, ], version = 1 ) abstract class MusicDatabase : RoomDatabase() { abstract fun musicDao(): MusicDao }

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DatabaseProcessingStep.kt class DatabaseProcessingStep

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DatabaseProcessingStep.kt class DatabaseProcessingStep : XProcessingStep { }

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DatabaseProcessingStep.kt class DatabaseProcessingStep : XProcessingStep { override fun process( ... ): Set { } }

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DatabaseProcessingStep.kt class DatabaseProcessingStep : XProcessingStep { override fun process( ... ): Set { val databases = elementsByAnnotation[Database::class.qualifiedName] ?.filterIsInstance() ?.mapNotNull { annotatedElement -> DatabaseProcessor(annotatedElement).process() } databases?.forEach { db -> // generate code } } }

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@Entity data class Song( @PrimaryKey val songId: Long ) // Access via property syntax val _songId = item.songId Entity Declaration // Access via property getter val _songId = item.getSongId(); Kotlin output Java output

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EntityProcessor.kt val getterCandidates = typeElement.getAllMethods()

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EntityProcessor.kt val getterCandidates = typeElement.getAllMethods().filter { it.element.parameters.isEmpty() && it.resolvedType.returnType.asTypeName() != XTypeName.UNIT_VOID }

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EntityProcessor.kt val getterCandidates = typeElement.getAllMethods().filter { it.element.parameters.isEmpty() && it.resolvedType.returnType.asTypeName() != XTypeName.UNIT_VOID } // ... getterCandidates.forEach { getter -> if (targetLanguage == CodeLanguage.KOTLIN) }

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XPoet A cross-language API mirrors JavaPoet and KotlinPoet APIs. • XTypeName: Represents a type name in Java and Kotlin's type system. • XFunSpec: Represents a Java/Kotlin function. • XCodeBlock: Represents a snippet of JPL/Kotlin code, supporting placeholders for values, names, types, and members. … and more!

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DatabaseWriter.kt fun create() : MusicDao { } MusicDao create() { } (Generated Code) Kotlin output Java output

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DatabaseWriter.kt fun create() : MusicDao { return MusicDao_Impl() } MusicDao create() { return new MusicDao_Impl(); } (Generated Code) Kotlin output Java output

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DatabaseWriter.kt private fun createFunction( dao: Dao ): FunSpec { return FunSpec.builder("create") .addModifiers(KModifier.PUBLIC) .returns(dao.typeName) .addStatement( "return %T", dao.implTypeName ).build() } private fun createFunction( dao: Dao ): MethodSpec { return MethodSpec.methodBuilder("create") .addModifiers(Modifier.PUBLIC) .returns(dao.typeName) .addStatement( "return new $T()", dao.implTypeName ).build() } KotlinPoet JavaPoet

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DatabaseWriter.kt (XPoet) private fun createFunction( codeLanguage: CodeLanguage, dao: Dao ): XFunSpec { }

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DatabaseWriter.kt (XPoet) private fun createFunction( codeLanguage: CodeLanguage, dao: Dao ): XFunSpec { return XFunSpec.builder(codeLanguage, "create", VisibilityModifier.PUBLIC).apply { }.build() }

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DatabaseWriter.kt (XPoet) private fun createFunction( codeLanguage: CodeLanguage, dao: Dao ): XFunSpec { return XFunSpec.builder(codeLanguage, "create", VisibilityModifier.PUBLIC).apply { returns(dao.typeName) addStatement( "return %L", XCodeBlock.ofNewInstance(codeLanguage, dao.implTypeName) ) }.build() }

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SQLite.kt package androidx.sqlite /** * Executes a single SQL statement that returns no values. */ fun SQLiteConnection.execSQL(sql: String) { prepare(sql).use { it.step() } }

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AutoMigrationWriter.kt public override fun migrate( ) { } @Override public void migrate( ) { } (Generated Code) Kotlin output Java output

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AutoMigrationWriter.kt public override fun migrate( connection: SQLiteConnection ) { } @Override public void migrate( @NonNull final SQLiteConnection connection ) { } (Generated Code) Kotlin output Java output

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AutoMigrationWriter.kt public override fun migrate( connection: SQLiteConnection ) { connection.execSQL("...") } @Override public void migrate( @NonNull final SQLiteConnection connection ) { SQLiteKt.execSQL(connection, "..."); } (Generated Code) Kotlin output Java output

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AutoMigrationWriter.kt override fun addDatabaseExecuteSqlStatement( migrateBuilder: XFunSpec.Builder, sql: String ) { migrateBuilder.addStatement( "%L", XCodeBlock.ofExtensionCall( language = codeLanguage, memberName = SQLiteDriverMemberNames.CONNECTION_EXEC_SQL, receiverVarName = "connection", args = XCodeBlock.of(codeLanguage, "%S", sql) ) ) }

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Compromise: “Java-ish Kotlin” public override fun listOfString(arg: List): MyEntity { } (Generated Code)

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Compromise: “Java-ish Kotlin” public override fun listOfString(arg: List): MyEntity { val _stringBuilder: StringBuilder = StringBuilder() ... } (Generated Code)

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Compromise: “Java-ish Kotlin” public override fun listOfString(arg: List): MyEntity { val _stringBuilder: StringBuilder = StringBuilder() _stringBuilder.append("SELECT * FROM MyEntity WHERE string IN (") val _inputSize: Int = arg.size appendPlaceholders(_stringBuilder, _inputSize) _stringBuilder.append(")") val _sql: String = _stringBuilder.toString() return performBlocking(__db, true, false) { _connection -> val _stmt: SQLiteStatement = _connection.prepare(_sql) try { var _argIndex: Int = 1 for (_item: String in arg) { _stmt.bindText(_argIndex, _item) _argIndex++ } ... (Generated Code)

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XProcessing Testing XProcessing Testing is an auxiliary API that simplifies testing across KAPT, KSP, and Javac environments. • Ensured backwards compatibility • Reduce test duplication due to various environments.

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DatabaseProcessorTest.kt val dbSrc = Source.kotlin( "MyDatabase.kt", """ """.trimIndent() )

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DatabaseProcessorTest.kt val dbSrc = Source.kotlin( "MyDatabase.kt", """ import androidx.room.* @Database(entities = [MyEntity::class], version = 1) abstract class MyDatabase """.trimIndent() ) : RoomDatabase

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DatabaseProcessorTest.kt val dbSrc = Source.kotlin( ... ) val entitySrc = Source.java( "MyEntity", """ import androidx.room.* class MyEntity { @PrimaryKey long id; } """.trimIndent() )

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DatabaseProcessorTest.kt @Test fun validateSuperclass() { runProcessorTest( sources = listOf(dbSrc, entitySrc), createProcessingSteps = { listOf(DatabaseProcessingStep()) } ) { } } Link: h tt ps://cs.android.com/.../room-compiler-processing-testing/src/.../ProcessorTestExt.kt

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DatabaseProcessorTest.kt @Test fun validateSuperclass() { runProcessorTest( sources = listOf(dbSrc, entitySrc), createProcessingSteps = { listOf(DatabaseProcessingStep()) } ) { result -> result.hasErrorContaining( "Classes annotated with @Database should extend androidx.room.RoomDatabase" ) } } Link: h tt ps://cs.android.com/.../room-compiler-processing-testing/src/.../ProcessorTestExt.kt

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The Conversion To KMP

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KMP SQLite & Build Process • Kotlin/Native’s Clang and sysroots to cross-compile SQLite • C-interop for SQLite access within Kotlin code • Development of bundled and framework SQLite drivers Link: h tt ps://developer.android.com/kotlin/multipla tf orm/sqlite

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Framework SQLite Android Common Native Android Native sqlite3.h android.database. SQLiteDatabase Android SQLite Driver Native SQLite Driver room-runtime sqlite-framework

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Common Bundled SQLite Android Common Native Android Native sqlite3.c sqlite_jni.cpp room-runtime sqlite-bundled Bundled SQLite Driver

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Maintaining Compatibility • Surveyed Room APIs • Move compatible APIs to common • Retain Android-only functionality

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Expect / Actuals // src/commonMain/.../FileLock.kt internal expect class FileLock(filename: String) { fun lock() fun unlock() } Strategy

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Expect / Actuals // src/nativeMain/.../FileLock.native.kt import platform.posix.* internal actual class FileLock actual constructor(filename: String) { Strategy

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Expect / Actuals // src/nativeMain/.../FileLock.native.kt import platform.posix.* internal actual class FileLock actual constructor(filename: String) { // src/androidJvmMain/.../FileLock.androidJvm.kt import java.io.* import java.nio.channels.* internal actual class FileLock actual constructor(filename: String) { Strategy

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Interfaces and Implementations // src/commonMain/.../SQLiteDriver.kt interface SQLiteDriver { fun open(fileName: String): SQLiteConnection } Strategy

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Interfaces and Implementations // src/nativeMain/.../NativeSQLiteDriver.native.kt class NativeSQLiteDriver : SQLiteDriver { override fun open(fileName: String): SQLiteConnection = memScoped { val dbPointer = allocPointerTo() val resultCode = sqlite3_open_v2( filename = fileName, ppDb = dbPointer.ptr, flags = SQLITE_OPEN_READWRITE or SQLITE_OPEN_CREATE, zVfs = null ) if (resultCode != SQLITE_OK) { throwSQLiteException(resultCode, null) } NativeSQLiteConnection(dbPointer.value!!) } } Strategy

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Interfaces and Implementations // src/androidJvmMain/.../BundledSQLiteDriver.androidJvm.kt actual class BundledSQLiteDriver : SQLiteDriver { override fun open(fileName: String): SQLiteConnection { val address = nativeOpen(fileName) return BundledSQLiteConnection(address) } private companion object { init { NativeLibraryLoader.loadLibrary("sqliteJni") } } } private external fun nativeOpen(name: String): Long Strategy

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Top-Level Declarations // src/commonMain/.../TableInfo.kt expect class TableInfo { override fun equals(other: Any?): Boolean override fun hashCode(): Int } Strategy

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Top-Level Declarations // src/commonMain/.../TableInfo.kt expect class TableInfo { override fun equals(other: Any?): Boolean override fun hashCode(): Int } internal fun TableInfo.equalsCommon(other: Any?): Boolean { // ... } internal fun TableInfo.hashCodeCommon(): Int { // ... } Strategy

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Top-Level Declarations // src/jvmNativeMain/.../TableInfo.jvmNative.kt actual class TableInfo { actual override fun equals(other: Any?) = equalsCommon(other) actual override fun hashCode() = hashCodeCommon() } // src/androidMain/.../TableInfo.android.kt actual class TableInfo { actual override fun equals(other: Any?) = equalsCommon(other) actual override fun hashCode() = hashCodeCommon() companion object { fun read(database: SupportSQLiteDatabase) { ... } } } Strategy

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Additional Problems • Heavy reliance on Executors, Runnables and Callables. • The use of reflection while accessing the generated database implementation.

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Reflection KMP fun createRoomDatabase() = Room.inMemoryDatabaseBuilder( context = appContext ).build() @Generated(value = ["androidx.room.RoomProcessor"]) public class MusicDatabase_Impl : MusicDatabase() { // ... } Class.forName(databaseClass + "_Impl")

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Reflection KMP fun createRoomDatabase() = Room.inMemoryDatabaseBuilder( context = appContext, factory = { MusicDatabase_Impl() } ).build() Link: h tt ps://youtrack.jetbrains.com/issue/KT-61724/Re fl ection-suppo rt -for-kmp @Generated(value = ["androidx.room.RoomProcessor"]) public class MusicDatabase_Impl : MusicDatabase() { // ... }

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Room’s Migration Journey Room KMP! Build XProcessing Add KSP support in room Move JPL sources to be Kotlin sources Add cross-platform SQLite support Migrate sources to use cross-platform SQLite drivers Generate cross-platform compatible code Add Kotlin code generation

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Kotlin Multiplatform’s Bright Future • Broadening Non-Android Support The alpha release marks a significant milestone in Room’s KMP journey, with non-Android platforms currently nearing full feature parity. • Expanded Platform Support Future development plans for Room include expansion to Web via SQLite WASM. • Google's Official Investment in KMP Room's adoption of KMP aligns with Google’s continued investment in KMP, contributing to the growth and success of the ecosystem.

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Libraries: Android vs KMP Language UI Image Loading DI Java, Kotlin Kotlin View, Jetpack Compose Compose Multiplatform Glide, Coil Coil Network Database Storage Preference, DataStore DataStore Retrofit Ktor Dagger, Hilt Koin, Kodein, kotlin-inject Room SQLDelight Android Kotlin Multiplatform ... ... ...

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Libraries: Android vs KMP Language UI Image Loading DI Java, Kotlin Kotlin View, Jetpack Compose Compose Multiplatform Glide, Coil Coil Network Database Storage Preference, DataStore DataStore Retrofit Ktor Dagger, Hilt Koin, Kodein, kotlin-inject Room 🆕 Room, SQLDelight Android Kotlin Multiplatform ... ... ... 🎉🎉

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੿ܻ • Room੉ KMPܳ ૑ਗೞחؘ ٜযр ֢۱: • KSP ૑ਗ (XProcessing, XPoet) • ࣗझ௏٘ ߂ ࢤࢿغח ௏٘ܳ Kotlinਵ۽ ੹ജ • SQLite ۄ੉࠳۞ܻ ௼۽झ೒ۖಬ ૑ਗ • Android জ ѐߊ੗ ੑ੢ীࢲ: • Breaking Changesח হ׮. • Data Migration হ੉, জਸ KMP۽ ഛ੢ೡ ࣻب ੓׮. • ׮݅ KMP۽ ഛ੢ೞ۰ݶ Room Migration੉ ೙ਃೞ׮. (SQLite Driver ١) Link: h tt ps://developer.android.com/training/data-storage/room/room-kmp-migration

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хࢎ೤פ׮!