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@marcoGomier
Marco Gomiero
Senior Android Developer @ Airalo
Google Developer Expert for Kotlin
From Android to
Multiplatform
and beyond
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@marcoGomier
• Started in 2016 as an Android library
RSSParser
• Time to make it Multiplatform!
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@marcoGomier
Project Structure
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@marcoGomier
Android Library Source Set
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@marcoGomier
Kotlin Multiplatform Source Sets
Android Library Source Set
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@marcoGomier
How to migrate to
Multiplaform source sets?
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@marcoGomier
* without losing git and contributors history
How to migrate to
Multiplaform source sets? *
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@marcoGomier
Create a new library project
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@marcoGomier
Create a new library project
https://terrakok.github.io/kmp-web-wizard/
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@marcoGomier
Create a new library project
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@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
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@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
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@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
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@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
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@marcoGomier
Platform-specific APIs
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@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
}
}
}
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@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
}
}
}
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@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
}
}
}
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@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
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@marcoGomier
🤔
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@marcoGomier
Expect/Actual
https://kotlinlang.org/docs/multiplatform-connect-to-apis.html
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@marcoGomier
internal interface XmlFetcher {
suspend fun fetchXml(url: String): ParserInput
}
Interface
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@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 ->
...
}
}
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@marcoGomier
internal interface XmlParser {
suspend fun parseXML(input: ParserInput): RssChannel
}
Interface
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@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()
...
}
}
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@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
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@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)
}
}
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@marcoGomier
Expect/Actual
internal expect class ParserInput
internal actual data class ParserInput(
val inputStream: InputStream
)
internal actual data class ParserInput(
val data: NSData
)
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@marcoGomier
Networking
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@marcoGomier
Ktor? OkHttp?
Platform-specific APIs?
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@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 ->
...
}
}
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@marcoGomier
Constructors
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@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
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@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
}
}
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@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,
),
)
}
}
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@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,
),
)
}
}
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@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,
),
)
}
}
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@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,
),
)
}
}
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@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
),
)
}
}
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@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
),
)
}
}
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@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
),
)
}
}
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@marcoGomier
Create an instance with default values
expect fun RssParser(): RssParser
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@marcoGomier
expect fun RssParser(): RssParser
actual fun RssParser(): RssParser = RssParserBuilder().build()
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@marcoGomier
Testing
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@marcoGomier
How to write one test
for multiple platforms?
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@marcoGomier
Create an instance with default values
internal expect object XmlParserFactory {
fun createXmlParser(): XmlParser
}
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@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())
}
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@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)
}
}
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@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)
}
}
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@marcoGomier
Test the Parser
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@marcoGomier
Test the Parser
• Run tests on all the platforms
• Run tests on a specific platform
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@marcoGomier
Test the Parser
• Run tests on all the platforms
• Run tests on a specific platform
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@marcoGomier
Test the Parser
• Run tests on all the platforms
• Run tests on a specific platform
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@marcoGomier
Test the Parser
• Run tests on all the platforms
• Run tests on a specific platform
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@marcoGomier
Test the Parser
• Run tests on all the platforms
• Run tests on a specific platform
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@marcoGomier
Test the Parser
• Run tests on all the platforms
• Run tests on a specific platform
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@marcoGomier
Test the Parser
• Run tests on all the platforms
• Run tests on a specific platform
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@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)
}
}
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@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)
}
}
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@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
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@marcoGomier
Use Environmental Variables!💡
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@marcoGomier
val rootDir = "${rootProject.rootDir.path}/rssparser/src/commonTest/resources"
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@marcoGomier
val rootDir = "${rootProject.rootDir.path}/rssparser/src/commonTest/resources"
tasks.withType().configureEach {
environment("TEST_RESOURCES_ROOT", rootDir)
}
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@marcoGomier
val rootDir = "${rootProject.rootDir.path}/rssparser/src/commonTest/resources"
tasks.withType().configureEach {
environment("TEST_RESOURCES_ROOT", rootDir)
}
tasks.withType().configureEach {
environment("TEST_RESOURCES_ROOT", rootDir)
}
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@marcoGomier
val rootDir = "${rootProject.rootDir.path}/rssparser/src/commonTest/resources"
tasks.withType().configureEach {
environment("TEST_RESOURCES_ROOT", rootDir)
}
tasks.withType().configureEach {
environment("TEST_RESOURCES_ROOT", rootDir)
environment("SIMCTL_CHILD_TEST_RESOURCES_ROOT", rootDir)
}
https://stackover
fl
ow.com/a/53604237/5264056
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@marcoGomier
Read files in tests
internal expect fun readFileFromResources(
resourceName: String
): ParserInput
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@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
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@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)
)
}
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@marcoGomier
Publishing
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@marcoGomier
• Nothing to do! \o/
Publishing
https://github.com/vanniktech/gradle-maven-publish-plugin
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@marcoGomier
Desktop (JVM), Android, iOS
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@marcoGomier
Desktop (JVM), Android, iOS, macOS, tvOS, watchOS*
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@marcoGomier
Maybe in the future
•JS
•WebAssembly
•Windows
•Linux
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@marcoGomier
Conclusions
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@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
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@marcoGomier https://github.com/prof18/RSS-Parser
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@marcoGomier https://thebakery.dev/52/
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@marcoGomier feed
fl
ow.dev/
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@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
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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/