From Android to Multiplatform and beyond | DevFest Hamburg

@marcoGomier Marco Gomiero Senior Android Developer @ Airalo Google Developer
Expert for Kotlin From Android to Multiplatform and beyond

@marcoGomier • Started in 2016 as an Android library RSSParser
• Time to make it Multiplatform!

@marcoGomier Project Structure

@marcoGomier Android Library Source Set

@marcoGomier Kotlin Multiplatform Source Sets Android Library Source Set

@marcoGomier How to migrate to Multiplaform source sets?

@marcoGomier * without losing git and contributors history How to
migrate to Multiplaform source sets? *

@marcoGomier Create a new library project

@marcoGomier Create a new library project https://terrakok.github.io/kmp-web-wizard/

@marcoGomier Create a new library project

@marcoGomier • Move the new source sets inside the existing
library project • Rename the old source set • Duplicate and keep the old source set in the repo (for reference) • Move the existing code to the androidMain source set • Make the Android part work as before without sharing The Recipe

@marcoGomier Platform-specific APIs

@marcoGomier RSSParser pre-multiplatform class Parser private constructor( private var callFactory:
Call.Factory, private val charset: Charset? = null, ) { suspend fun getChannel(url: String): Channel = withContext(coroutineContext) { // If the charset is null, then "null" is saved in the database. // It's easier for retrieving data afterwards val charsetString = charset.toString() val cachedFeed = cacheManager?.getCachedFeed(url, charsetString) if (cachedFeed != null) { Log.d(TAG, "Returning object from cache") return@withContext cachedFeed } else { Log.d(TAG, "Returning data from network") val xml = CoroutineEngine.fetchXML(url, callFactory) val channel = CoroutineEngine.parseXML(xml, charset) cacheManager?.cacheFeed( url = url, channel = channel, charset = charsetString, ) return@withContext channel } } }

@marcoGomier suspend fun getChannel(url: String): Channel = withContext(coroutineContext) { //
If the charset is null, then "null" is saved in the database. // It's easier for retrieving data afterwards val charsetString = charset.toString() val cachedFeed = cacheManager?.getCachedFeed(url, charsetString) if (cachedFeed != null) { Log.d(TAG, "Returning object from cache") return@withContext cachedFeed } else { Log.d(TAG, "Returning data from network") val xml = CoroutineEngine.fetchXML(url, callFactory) val channel = CoroutineEngine.parseXML(xml, charset) cacheManager?.cacheFeed( url = url, channel = channel, charset = charsetString, ) return@withContext channel } } }

@marcoGomier class Parser private constructor( private var callFactory: Call.Factory, private
val charset: Charset? = null, ) { suspend fun getChannel(url: String): Channel = withContext(coroutineContext) { // If the charset is null, then "null" is saved in the database. // It's easier for retrieving data afterwards val charsetString = charset.toString() val cachedFeed = cacheManager?.getCachedFeed(url, charsetString) if (cachedFeed != null) { Log.d(TAG, "Returning object from cache") return@withContext cachedFeed } else { Log.d(TAG, "Returning data from network") val xml = CoroutineEngine.fetchXML(url, callFactory) cacheManager?.cacheFeed( url = url, channel = channel, charset = charsetString, ) return@withContext channel } } } import okhttp3.Call import okhttp3.Callback import okhttp3.Request import okhttp3.Response val channel = CoroutineEngine.parseXML(xml, charset) cacheManager?.cacheFeed( url = url, channel = channel, import org.xmlpull.v1.XmlPullParser import org.xmlpull.v1.XmlPullParserFactory

@marcoGomier 🤔

@marcoGomier Expect/Actual https://kotlinlang.org/docs/multiplatform-connect-to-apis.html

@marcoGomier internal interface XmlFetcher { suspend fun fetchXml(url: String): ParserInput
} Interface

@marcoGomier internal interface XmlFetcher { suspend fun fetchXml(url: String): ParserInput
} internal class JvmXmlFetcher( private val callFactory: Call.Factory, ): XmlFetcher { override suspend fun fetchXml(url: String): ParserInput { val request = createRequest(url) return ParserInput( inputStream = callFactory.newCall(request).await() ) } } internal class IosXmlFetcher( private val nsUrlSession: NSURLSession, ): XmlFetcher { override suspend fun fetchXml(url: String): ParserInput = suspendCancellableCoroutine { continuation -> ... } }

@marcoGomier internal interface XmlParser { suspend fun parseXML(input: ParserInput): RssChannel
} Interface

@marcoGomier internal class AndroidXmlParser( private val dispatcher: CoroutineDispatcher, ) :
XmlParser { override suspend fun parseXML(input: ParserInput): RssChannel = withContext(dispatcher) { val factory = XmlPullParserFactory.newInstance() ... } } internal interface XmlParser { suspend fun parseXML(input: ParserInput): RssChannel } internal class IosXmlParser( private val dispatcher: CoroutineDispatcher, ) : XmlParser { override suspend fun parseXML(input: ParserInput): RssChannel = withContext(dispatcher) { suspendCancellableCoroutine { continuation -> ... } } } internal class JvmXmlParser( private val dispatcher: CoroutineDispatcher, ) : XmlParser { override suspend fun parseXML(input: ParserInput): RssChannel = withContext(dispatcher) { val parser = SAXParserFactory.newInstance().newSAXParser() ... } }

@marcoGomier class RssParser internal constructor( private val xmlFetcher: XmlFetcher, private
val xmlParser: XmlParser, ) { suspend fun getRssChannel(url: String): RssChannel = withContext(coroutineContext) { val parserInput = xmlFetcher.fetchXml(url) return@withContext xmlParser.parseXML(parserInput) } } @marcoGomier

@marcoGomier Prefer interfaces, if possible class RssParser internal constructor( private
val xmlFetcher: XmlFetcher, private val xmlParser: XmlParser, ) { suspend fun getRssChannel(url: String): RssChannel = withContext(coroutineContext) { val parserInput = xmlFetcher.fetchXml(url) return@withContext xmlParser.parseXML(parserInput) } }

@marcoGomier Expect/Actual internal expect class ParserInput internal actual data class
ParserInput( val inputStream: InputStream ) internal actual data class ParserInput( val data: NSData )

@marcoGomier Networking

@marcoGomier Ktor? OkHttp? Platform-specific APIs?

@marcoGomier • Keep using OKhttp on Android and JVM •
Use NSURLSession on iOS • Backward compatibility and popularity internal class JvmXmlFetcher( private val callFactory: Call.Factory, ): XmlFetcher { override suspend fun fetchXml(url: String): ParserInput { val request = createRequest(url) return ParserInput( inputStream = callFactory.newCall(request).await() ) } } internal class IosXmlFetcher( private val nsUrlSession: NSURLSession, ): XmlFetcher { override suspend fun fetchXml(url: String): ParserInput = suspendCancellableCoroutine { continuation -> ... } }

@marcoGomier Constructors

@marcoGomier Creating an RssParser Instance • Create an instance with
platform-specific dependencies (OkHttp, NSURLSession) • Create an instance with default values • Create an instance from a KMP, Android, or JVM project

@marcoGomier Create an instance with platform-specific dependencies class RssParser internal
constructor( private val xmlFetcher: XmlFetcher, private val xmlParser: XmlParser, ) { internal interface Builder { fun build(): RssParser } }

@marcoGomier class RssParserBuilder( private val callFactory: Call.Factory = OkHttpClient(), private
val charset: Charset? = null, ): RssParser.Builder { override fun build(): RssParser { return RssParser( xmlFetcher = JvmXmlFetcher( callFactory = callFactory, ), xmlParser = AndroidXmlParser( charset = charset, dispatcher = Dispatchers.IO, ), ) } }

@marcoGomier class RssParserBuilder( private val callFactory: Call.Factory = OkHttpClient(), private
val charset: Charset? = null, ): RssParser.Builder { override fun build(): RssParser { return RssParser( xmlFetcher = JvmXmlFetcher( callFactory = callFactory, ), xmlParser = JvmXmlParser( charset = charset, dispatcher = Dispatchers.IO, ), ) } }

@marcoGomier class RssParserBuilder( private val nsUrlSession: NSURLSession = NSURLSession.sharedSession, ):
RssParser.Builder { override fun build(): RssParser { return RssParser( xmlFetcher = IosXmlFetcher( nsUrlSession = nsUrlSession, ), xmlParser = IosXmlParser( Dispatchers.IO ), ) } }

@marcoGomier Create an instance with default values expect fun RssParser():
RssParser

@marcoGomier expect fun RssParser(): RssParser actual fun RssParser(): RssParser =
RssParserBuilder().build()

@marcoGomier Testing

@marcoGomier How to write one test for multiple platforms?

@marcoGomier Create an instance with default values internal expect object
XmlParserFactory { fun createXmlParser(): XmlParser }

@marcoGomier internal expect object XmlParserFactory { fun createXmlParser(): XmlParser }
internal actual object XmlParserFactory { actual fun createXmlParser(): XmlParser = JvmXmlParser(dispatcher = UnconfinedTestDispatcher()) } internal actual object XmlParserFactory { actual fun createXmlParser(): XmlParser = AndroidXmlParser(dispatcher = UnconfinedTestDispatcher()) } internal actual object XmlParserFactory { actual fun createXmlParser(): XmlParser = IosXmlParser(dispatcher = UnconfinedTestDispatcher()) }

@marcoGomier Test the Parser class XmlParserTest { @Test fun channelTitle_isCorrect()
= runTest { val parser = XmlParserFactory.createXmlParser() val input = readFileFromResources("test-feed.xml") val channel = parser.parseXML(input) assertEquals("channel-title", channel.title) } }

@marcoGomier Test the Parser

@marcoGomier Test the Parser • Run tests on all the
platforms • Run tests on a specific platform

@marcoGomier Test the Parser class XmlParserTest { @Test fun channelTitle_isCorrect()
= runTest { val parser = XmlParserFactory.createXmlParser() val input = readFileFromResources("test-feed.xml") val channel = parser.parseXML(input) assertEquals("channel-title", channel.title) } }

@marcoGomier Gradle sets the test process's working directory to the
module's directory Read files in tests but ... • No java.io.File on Kotlin/Native • On iOS, the working directory is unrelated to the project directory

@marcoGomier Use Environmental Variables!💡

@marcoGomier val rootDir = "${rootProject.rootDir.path}/rssparser/src/commonTest/resources"

@marcoGomier val rootDir = "${rootProject.rootDir.path}/rssparser/src/commonTest/resources" tasks.withType<Test>().configureEach { environment("TEST_RESOURCES_ROOT", rootDir) }

tasks.withType<KotlinNativeTest>().configureEach { environment("TEST_RESOURCES_ROOT", rootDir) }

tasks.withType<KotlinNativeTest>().configureEach { environment("TEST_RESOURCES_ROOT", rootDir) environment("SIMCTL_CHILD_TEST_RESOURCES_ROOT", rootDir) } https://stackover fl ow.com/a/53604237/5264056

@marcoGomier Read files in tests internal expect fun readFileFromResources( resourceName:
String ): ParserInput

@marcoGomier internal actual fun readFileFromResources( resourceName: String, ): ParserInput {
val path = System.getenv("TEST_RESOURCES_ROOT") val file = File("$path/$resourceName") return ParserInput( inputStream = FileInputStream(file) ) } internal expect fun readFileFromResources( resourceName: String ): ParserInput

@marcoGomier internal expect fun readBinaryResource( resourceName: String, ): ParserInput internal
actual fun readFileFromResources( resourceName: String ): ParserInput { val s = getenv("TEST_RESOURCES_ROOT")?.toKString() val path = "$s/${resourceName}" val data = NSData.dataWithContentsOfFile(path) return ParserInput(requireNotNull(data)) } internal actual fun readFileFromResources( resourceName: String, ): ParserInput { val path = System.getenv("TEST_RESOURCES_ROOT") val file = File("$path/$resourceName") return ParserInput( inputStream = FileInputStream(file) ) }

@marcoGomier Publishing

@marcoGomier • Nothing to do! \o/ Publishing https://github.com/vanniktech/gradle-maven-publish-plugin

@marcoGomier Desktop (JVM), Android, iOS

@marcoGomier Desktop (JVM), Android, iOS, macOS, tvOS, watchOS*

@marcoGomier Maybe in the future •JS •WebAssembly •Windows •Linux

@marcoGomier Conclusions

@marcoGomier Conclusions • Adapting to different platforms requires time and
thinking • Code organisation can be challenging, especially for maintaining git history • Prefer Interfaces over expect/actual, where possible

@marcoGomier https://github.com/prof18/RSS-Parser

@marcoGomier https://thebakery.dev/52/

@marcoGomier feed fl ow.dev/

@marcoGomier Thank you! > Twitter: @marcoGomier > Github: prof18 >
Website: marcogomiero.com > Mastodon: androiddev.social/@marcogom Marco Gomiero Senior Android Developer @ Airalo Google Developer Expert for Kotlin

Bibliography / Useful Links • https: // kotlinlang.org/docs/multiplatform-mobile-understand-project- structure.html#source-sets •
https: // kotlinlang.org/docs/multiplatform-connect-to-apis.html • https: // square.github.io/okhttp/ • https: // ktor.io/ • https: // developer.apple.com/documentation/foundation/nsurlsession • https: // kotlinlang.org/docs/multiplatform-run-tests.html • https: // publicobject.com/2023/04/16/read-a-project-file-in-a-kotlin-multiplatform-test/ • https: // github.com/vanniktech/gradle-maven-publish-plugin • https: // github.com/prof18/RSS-Parser • https: // thebakery.dev/52/ • https: // www.feedflow.dev/

From Android to Multiplatform and beyond | DevF...

From Android to Multiplatform and beyond | DevFest Hamburg

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