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Introducing Kotlin in
Android Project
# B L R K O T L I N
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Senior Android Developer
Amadeus Software Labs
Hello!
I am Jitin Sharma
@js_2892
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About the App
Uses a lot of open libraries from Timber to Play Services
Completely written in Java
Already in production with multiple customers and million plus downloads
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Where we stood
~45000
255
lines of code
java classes
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WHY KOTLIN
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Immutability
Type/Null Safety
Extensions Lambdas
Interoperability
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SAFETY AND
IMMUTABILITY
Nullability makes you rethink your life choices.
Immutability makes you appreciate final keyword in Java
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STANDARD LIBRARY
supportActionBar?.apply {
setDisplayHomeAsUpEnabled(true)
setDisplayShowHomeEnabled(true)
}
if (getArguments() != null) {
}
arguments?.let{
}
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SO MANY STANDARDS
config?.decoderParams?.enabled = true
config?.decoderParams?.redundancy = true
config?.decoderParams?.length1 = 2
config?.decoderParams?.length2 = 16
config?.decoderParams?.apply {
enabled = true
redundancy = true
length1 = 2
length2 = 16
}
config?.decoderParams?.run {
enabled = true
redundancy = true
length1 = 2
length2 = 16
}
config?.decoderParams?.let {
it.enabled = true
it.redundancy = true
it.length1 = 2
it.length2 = 16
}
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STANDARD LIBRARY
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https://medium.com/@elye.project/mastering-kotlin-standard-functions-run-with-let-also-and-apply-9cd334b0ef84
HOW TO STANDARD.KT
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SWITCH to WHEN
Java Kotlin
• Direct assignment to variable as an result of when closure
if (fragment instanceof HomeFragment) {
// Logic here
}
val view = when (viewType) {
1 -> layoutInflater.inflate(R.layout.item_pax_checkbox, parent, false)
else -> layoutInflater.inflate(R.layout.item_pax_type, parent, false)
}
when(fragment) {
is HomeFragment -> {
}
}
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BYE BYE BUTTERKNIFE
• Usage in ViewHolders - still experimental
• Using override method onViewCreated instead of onCreateView in Fragments
Java Kotlin
@BindView(R.id.bottomLayout)
LinearLayout bottomLayout;
import kotlinx.android.synthetic.main.activity_main.*
bottomLayout.forEachChild {
}
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EXTENSION FUNCTIONS
fun View.show() {
this.visibility = View.VISIBLE
}
fun Context.dpToPx(dp : Int): Float {
val displayMetrics = this.resources.displayMetrics
return Math.round(dp * (displayMetrics.xdpi /
DisplayMetrics.DENSITY_DEFAULT)).toFloat()
}
fun Drawable.withTint(colorInt: Int): Drawable {
return with(this) {
DrawableCompat.wrap(this).apply {
DrawableCompat.setTint(this, colorInt)
}
}
}
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EXTENSION FUNCTIONS
Java Kotlin
fun ImageView.loadImage(url: String) {
Picasso.with(context)
.load(url)
.into(this)
}
Helper.loadImage(banner, "https://"); cityImageView.loadImage(destination.imageUrl)
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SUPER-POWERED DATA CLASSES
@Parcelize
data class City(var name: String? = null, var code: Int = 0) : Parcelable
copy()
equals()
hashcode()
newArray()
writeToParcel()
createFromParcel()
describeContents()
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VISIBILITY
private public
protected internal
• By default, everything is public
• All classes are declared final by default. Use open to make classes extendible.
• Subclasses should be defined as inner to access variables of outer class(useful in ViewHolders)
File level Module Level Everywhere
Subclass level
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S’MORE FEATURES
typealias SessionData = ArrayList>
tailrec fun HashMap.colorFinder(key: String): String? {
val value = this[key] as String
return if (value.startsWith("#")) {
value
} else {
this.colorFinder(value)
}
}
val appVersion: String
get() = BuildConfig.VERSION_NAME
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INTEROPERABILITY
becomes a priority when inheriting a large java codebase
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HANDLING INTEROP
• In most cases Kotlin automatically takes care of interoperability.
• void is converted to Unit when calling in Kotlin.
• Empty getters and setters are converted to Properties.
• Annotations in Java are respected by Kotlin to specify nullability of a certain variable.
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FROM API 27, ANDROID ALSO
HELPED
@Nullable
final public FragmentActivity getActivity() {
return mHost == null ? null : (FragmentActivity) mHost.getActivity();
}
Fragment.java(API 27)
• context, activity and bundle with Nullable annotation are no longer platform types.
• It’s always good to use Annotations on existing java code which could be used in Kotlin
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JVM ANNOTATIONS
class RequestCreator {
companion object {
fun buildUri(baseUrl: String): Uri {
return Uri.parse(baseUrl).buildUpon().build()
}
}
}
RequestCreator.Companion.buildUri(“https://");
RequestCreator.buildUri("https://")
Java
Kotlin
RequestCreator.kt
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JVM ANNOTATIONS
class RequestCreator {
companion object {
@JvmStatic fun buildUri(baseUrl: String): Uri {
return Uri.parse(baseUrl).buildUpon().build()
}
}
}
RequestCreator.buildUri("https://");
RequestCreator.buildUri("https://")
Java
Kotlin
RequestCreator.kt
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JVM ANNOTATIONS
fun ImageView.loadImage(url: String) {
Picasso.with(context)
.load(url)
.into(this)
}
HelperKt.loadImage(banner, "https://");
Java
Helper.kt
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JVM ANNOTATIONS
@file:JvmName("Helper")
package ...
import ...
fun ImageView.loadImage(url: String) {
Picasso.with(context)
.load(url)
.into(this)
}
Helper.loadImage(banner, "https://");
Java
Helper.kt
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JVM ANNOTATIONS
@JvmName("stringToIntSafely")
fun String.toIntSafely() {
try {
this.toInt()
} catch (_: Throwable) { }
}
Helper.stringToIntSafely(request.getId());
arguments?.getString("id")?.toIntSafely()
Java
Kotlin
Helper.kt
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EXCEPTION HANDLING
@Throws(Exception::class)
fun exceptionalLogic() {
}
try {
caller.exceptionalLogic();
} catch (Exception e) {
e.printStackTrace();
}
caller.exceptionalLogic()
Java
Kotlin
Helper.kt
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INTEROP WITH LAMBDAS
class Caller {
fun init(listener: (value: Int) -> Unit) {
// Logic here
}
}
caller.init { value: Int -> }
Kotlin
Caller.kt
Java ??? No support for Lambda in Java 7
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class Caller {
fun init(listener: SelectionListener) {
}
}
caller.init(object : SelectionListener {
override fun selected(value: Int) {
}
})
Kotlin
Caller.kt
Java
caller.init(new SelectionListener() {
@Override
public void selected(int value) {
}
});
interface SelectionListener {
fun selected(value: Int)
}
SelectionListener.kt
No SAM conversion for Kotlin interface :(
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class Caller {
fun init(listener: SelectionListener) {
}
}
caller.init(SelectionListener {
})
Kotlin
Caller.kt
Java
caller.init(new SelectionListener() {
@Override
public void selected(int value) {
}
});
interface SelectionListener {
void selected(int value);
}
SelectionListener.java
Automatic SAM conversion for Java interface :)
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WHAT ABOUT JAVA 8
April 2016 Support for Java 8 announced with Jack toolchain
March 2017 Jack toolchain is deprecated
April 2017 Java 8 support is merged into dx toolchain
May 2017 Kotlin is announced as first class language for Android
Nobody cares about Java 8 anymore
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TRY JAVA 8?
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INTEROP WITH JAVA 8
class Caller {
fun init(listener: (value: Int) -> Unit) {
// Logic here
}
}
caller.init { value: Int -> }
Kotlin
Caller.kt
Java
caller.init(value -> {
return Unit.INSTANCE;
});
Return type necessary in Java lambdas
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THAT MEANS…
list.filter { it.startsWith("0") }.map { it.toInt() }
Kotlin
Java
List filtered = filter(list, value -> value.startsWith("0"));
List mapped = map(list, Integer::parseInt);
Statically import methods from Kotlin Collection framework
• Kotlin Utility methods could be directly used in your Java code.
More idiomatic usage in Kotlin, but still…
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THAT MEANS…
Kotlin Java
• Create your own Utils with higher order functions
debugMode {
StrictMode.enableDefaults()
}
debugMode(() -> {
StrictMode.enableDefaults();
return Unit.INSTANCE;
});
inline fun debugMode(block: () -> Unit) {
if (BuildConfig.DEBUG) {
block()
}
}
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LINT AND CODE STYLE
• Relying mostly on Android Studio lint checks for Kotlin.
• Android now has a dedicated style guide and interop guide for Kotlin.
• https://android.github.io/kotlin-guides/style.html
• https://android.github.io/kotlin-guides/interop.html
• https://github.com/shyiko/ktlint
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AS 3.2 LINT UPDATES
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BUSINESS AS USUAL
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IMPACTS
When things weren’t cool
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BUILD
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BUILD
• CI server build time increased by 30-50%.
• Kotlin’s compilation time is slower for clean builds.
• However incremental compilation is faster than Java(enabled by default from 1.1.1).
• Android Studio builds generally showed a difference of 10-20% as we moved from
Gradle 2.14 -> 4.1, Kotlin 1.1.x -> 1.2.x
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JUnit testcases
with Robolectric
and Mockito
Publish results to
Sonarqube
dashboard
Jenkins for CI
Code in bitbucket
HIGHER LEVEL WORKFLOW
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TESTING AND QUALITY
• Test cases were written in Kotlin.
• Jacoco didn’t provide any coverage reports for Kotlin.
• Sonarqube dashboard was affected due to unavailability of code coverage for Kotlin.
When we started
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TESTING AND QUALITY
• Jacoco problem resolved by resolving correct class directories.
• Sonarqube code coverage works fine as it uses Jacoco binary.
• Jacoco has teeny tiny issues with generated methods.
• Kotlin is still not supported by Sonarqube officially(third party plugins are present, though)
• Quality checks and line-by-line coverage not available on Sonarqube
Where we are now
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Where we started
~45000
255
lines of code
java classes
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Baby Steps
~45000
250
lines of code
Java classes
30
~5000
Kotlin classes
lines of code
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WHAT WE ACHIEVED
• Significantly lower rates of crashes in Kotlin files.
• Better Kotlin education among developers.
• Newer projects migrated to Kotlin completely.
• Backend team also want a piece of Kotlin(probably got fed up of our bad java puns).
• Human interaction with iOS Developers (Swift <=> Kotlin).
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Thanks!
twitter.com/@js_2892
Any questions?