Kotlin is a modern statically typed programming language which was made a first-class language for writing Android Apps by Google in 2017. Since then it has grown into popularity and many apps from hottest startups to 500 fortune companies are built using Kotlin. This talk will deep dive into Kotlin and modern android architecture for writing apps faster and in a better way.

1. K O T L I N F O R A N D R O I D
D E V E L O P E R S
H A S S A N A B I D

2. C O N T E N T
• Why Kotlin
• Kotlin 101
• Kotlin vs. Java
• Advance Kotlin Topics
• Q & A

4. K O T L I N O N A N D R O I D S I N C E 2 0 1 7

5. K O T L I N 1 0 1
• It’s developed by JetBrains, and the fact that these are
the people behind a suite of IDEs, such as IntelliJ
• It’s pragmatic and concise, and makes coding a
satisfying and efficient experience.
• Kotlin is 100% interoperable with Java

6. S Y N TA X ( C L A S S )
class Foo {
val b: String = "b" // val means unmodifiable
var i: Int = 0 // var means modifiable
fun hello() {
val str = "Hello"
print("$str World")
}
fun sum(x: Int, y: Int): Int {
return x + y
}
fun maxOf(a: Float, b: Float) = if (a > b) a else b
}
S I N G L E L I N E
F U N C T I O N

7. S T R I N G I N T E R P O L AT I O N
// Java’s String.format() was built into the language
val x = 4
val y = 7
print("sum of $x and $y is ${x + y}") // sum of 4 and 7 is 11

8. T Y P E I N F E R E N C E
val a = "abc" // type inferred to String
val b = 4 // type inferred to Int
val c: Double = 0.7 // type declared explicitly
val d: List<String> = ArrayList() // type declared explicitly

9. S M A R T C A S T S
/* The Kotlin compiler tracks your logic and auto-casts types
if possible, which means no more instanceof checks
followed by explicit casts
*/
if (obj is String) {
print(obj.toUpperCase()) // obj is now known to be a String
}

10. I N T U I T I V E E Q U A L S
// no need to call equals()
val john1 = Person("John")
val john2 = Person("John")
john1 == john2 // true (structural equality)
john1 === john2 // false (referential equality)

11. D E FA U LT A R G U M E N T S
fun build(title: String, width: Int = 800, height: Int = 600) {
Frame(title, width, height)
}

12. N A M E D A R G U M E N T S
build("PacMan", 400, 300) // equivalent
build(title = "PacMan", width = 400, height = 300) // equivalent
build(width = 400, height = 300, title = "PacMan") // equivalent

13. W H E N E X P R E S S I O N ( S W I T C H )
when (x) {
1 -> print("x is 1")
2 -> print("x is 2")
3, 4 -> print("x is 3 or 4")
in 5..10 -> print("x is 5, 6, 7, 8, 9, or 10")
else -> print("x is out of range")
}
val res: Boolean = when {
obj == null -> false
obj is String -> true
else -> throw IllegalStateException()
}

14. P R O P E R T I E S
/*
Custom set & get behavior can be added to public fields,
which means we can stopbloating our code with mindless
getters & setters.
*/
class Frame {
var width: Int = 800
var height: Int = 600
val pixels: Int
get() = width * height
}

15. D E S T R U C T U R I N G D E C L A R AT I O N S
for ((key, value) in map) {
print("Key: $key")
print("Value: $value")
}

16. R A N G E S
for (i in 1..100) { ... }
for (i in 0 until 100) { ... }
for (i in 2..10 step 2) { ... }
for (i in 10 downTo 1) { ... }
if (x in 1..10) { ... }

17. E X T E N S I O N F U N C T I O N S
fun String.replaceSpaces(): String {
return this.replace(' ', '_')
}
val formatted = str.replaceSpaces()

18. N U L L S A F E T Y
/* Java is what we should call an almost statically typed language.
In it, a variable of type String is not guaranteed to
refer to a String— it might refer to null
*/
// Java developers have to live in constant fear of NPEs.
/* Kotlin resolves this by distinguishing between non-null
types and nullable types. Types are non-null by default,
and can be made nullable by adding a ? like so:
*/
var a: String = "abc"
a = null // compile error
var b: String? = "xyz"
b = null // no problem

19. N U L L S A F E T Y
//Kotlin forces you to guard against NPEs whenever
// you access a nullable type:
val x = b.length // compile error: b might be null
if (b == null) return
val x = b.length // no problem
/* We could also use a safe call ?.,
which evaluates to null instead of throwing a NPE:
*/
val x = b?.length // type of x is nullable Int

20. B E T T E R L A M A D A S
val sum = { x: Int, y: Int -> x + y } // type: (Int, Int) -> Int
val res = sum(4,7) // res == 11
numbers.filter({ x -> x.isPrime() })
numbers.filter { x -> x.isPrime() }
numbers.filter { it.isPrime() }

21. B E T T E R L A M A D A S
persons
.filter { it.age >= 18 }
.sortedBy { it.name }
.map { it.email }
.forEach { print(it) }

22. B E T T E R L A M A D A S
verticalLayout {
padding = dip(30)
editText {
hint = “Name”
textSize = 24f
}
editText {
hint = “Password”
textSize = 24f
}
button(“Login”) {
textSize = 26f
}
}

23. S C O P I N G F U N C T I O N S
// 1. with
val person: Person = getPerson()
with(person) {
print(name)
print(age)
}
// 2. apply
val peter = Person().apply {
// only access properties in apply block!
name = "Peter"
age = 18
}

24. S C O P I N G F U N C T I O N S
// 3. let
getNullablePerson()?.let {
// only executed when not-null
promote(it)
}
// 4. run
val inserted: Boolean = run {
val person: Person = getPerson()
val personDao: PersonDao = getPersonDao()
personDao.insert(person)
}
fun printAge(person: Person) = person.run {
print(age)
}

25. S C O P I N G F U N C T I O N S
private fun insert(user: User) = SqlBuilder().apply {
append("INSERT INTO user (email, name, age) VALUES ")
append("(?", user.email)
append(",?", user.name)
append(",?)", user.age)
}.also {
print("Executing SQL update: $it.")
}.run {
jdbc.update(this) > 0
}

27. K O T L I N E X T E N S I O N S -
K T X

28. K O T L I N E X T E N S I O N S F O R A N D R O I D
• Makes Android development more concise, pleasant
and idiomatic
• Writing clean, readable code is a lot easier and a lot
more fun

29. K T X E X A M P L E
view.addOnLayoutChangeListener(object : View.OnLayoutChangeListener
{ override fun onLayoutChange(
view: View?,
left: Int,
top: Int,
right: Int,
bottom: Int,
oldLeft: Int,
oldTop: Int,
oldRight: Int,
oldBottom: Int
){
doSomething()
} })

30. K T X E X A M P L E
view.addOnLayoutChangeListener(object : View.OnLayoutChangeListener
{ override fun onLayoutChange(
view: View?,
left: Int,
top: Int,
right: Int,
bottom: Int,
oldLeft: Int,
oldTop: Int,
oldRight: Int,
oldBottom: Int
){
doSomething()
} })
// KTX
view.doOnNextLayout { doSomething() }
S I N G L E L I N E
F U N C T I O N

31. A D D K T X I N Y O U R P R O J E C T
repositories {
google()
}
dependencies {
implementation 'androidx.core:core-ktx:1.0.0' }

32. A D D K T X I N Y O U R P R O J E C T
repositories {
google()
}
dependencies {
implementation 'androidx.core:core-ktx:1.0.0' }

33. M O R E K T X L I B S
androidx.core:core-ktx
androidx.fragment:fragment-ktx
androidx.palette:palette-ktx
androidx.sqlite:sqlite-ktx
androidx.collection:collection-ktx
androidx.lifecycle:lifecycle-viewmodel-ktx
androidx.lifecycle:lifecycle-reactivestreams-ktx
android.arch.navigation:navigation-common-ktx
android.arch.navigation:navigation-fragment-ktx
android.arch.navigation:navigation-runtime-ktx
android.arch.navigation:navigation-testing-ktx
android.arch.navigation:navigation-ui-ktx
android.arch.work:work-runtime-ktx

34. N A M E D PA R A M S A N D D E FA U LT VA L U E S
// Original drawable.setBounds(drawable.bounds.left,
drawable.bounds.top, drawable.bounds.right, 100)
// KTX
drawable.updateBounds(bottom = 100)

35. N A M E D PA R A M S A N D D E FA U LT VA L U E S
// Original
animator.addListener(object : Animator.AnimatorListener {
override fun onAnimationEnd(a: Animator?) { ... }
override fun onAnimationStart(a: Animator?) { }
override fun onAnimationCancel(a: Animator?) { }
override fun onAnimationRepeat(a: Animator?) { }
})
// KTX
animator.addListener(onEnd = { ... })
animator.doOnEnd { ... }

36. O P E R AT O R O V E R L O A D I N G
// Original
bitmap.getPixel(100, 100)
// KTX
bitmap[100, 100]

37. O P E R AT O R O V E R L O A D I N G
// Original
menu.removeItem(menuItem.itemId)
// KTX
menu -= menuItem

38. D E S T R U C T U R I N G
// Original
val lat = location.latitude
val long = location.longitude
// KTX
val (lat, long) = location

39. M O R E K T X E X A M P L E S
// Original
viewGroup.childCount != 0
// KTX
viewGroup.isEmpty() viewGroup.isNotEmpty()
// Original
for (index in 0 until viewGroup.childCount)
{ doSomething(viewGroup.getChildAt(index))
}x
// KTX
viewGroup.forEach { doSomething() }

40. M O R E K T X E X A M P L E S
// Original sharedPrefs.edit()
.putBoolean(key, valuex) .apply()
// KTX
sharedPrefs.edit { putBoolean(key, value) }
// Original
val builder = SpannableStringBuilder()
val start = builder.length builder.append("Hello") builder.setSpan(
StyleSpan(Typeface.BOLD),
start,
builder.length, Spanned.SPAN_INCLUSIVE_EXCLUSIVE
)
// KTX
builder.bold { append("Hello") }
builder.bold { italic { underline { append("Hello") } } }

41. K O T L I N C O R O U N T I N E S

42. C O R O U T I N E S
• Light-weight threads (for async programming)
• Alternative to Rx-Java

43. S I M P L E A P P A R C H I T E C T U R E

44. C L E A N A R C H I T E C T U R E

45. O P E N S O U R C E C O D E
• https://github.com/nickbutcher/plaid
• https://github.com/googlesamples/android-sunflower
• https://github.com/bufferapp/android-clean-
architecture-boilerplate

46. L E A R N I N G M AT E R I A L
• Udacity
• https://www.udacity.com/course/developing-
android-apps-with-kotlin--ud9012

47. Q U E S T I O N S ?

48. T H A N K Y O U