LezhinComics는 Kotlin을 어떻게 적용 하고 있을까?

1. 레진코믹스는 Kotlin을
어떻게 사용 하고 있을
까?
LazySoul
우명인

2. Why Kotlin ?
• Java 와 100% Interop
• 람다식, Higher-order function 사용 가능
• Java8은 가능 하지만, Android는 Java8을 제한적으로 사
용
• 보일러 플레이트들이 적음 (property, data class,
lambda…)
• null safe, kotlin extensions, collection Api, Lazy evaluation
…..

3. Why Java ?
• 익숙함?
• ……(성능?)

4. 현재상황
Kotlin > Java

5. 현재상황

6. 현재상황
>
54
%
45
%
1%

7. 현재상황
새로 작성 되는 코드들은 Kotlin

8. 현재상황
기존 Java 코드를 수정해야 되는 경우, 시간적 여유가 있다면
Kotlin으로 변환

9. 현재상황
리펙토링이 필요 할때 되도록 Kotlin으로

10. 현재상황?
• 굳이 Java 코드를 Kotlin 으로 100% 바꿀 필요가 있을까?

11. 현재상황?
• 굳이 Java 코드를 Kotlin 으로 100% 바꿀 필요가 있을까?
• 새로 작성 하는 코드는 Kotlin으로 작성 할 필요가 있을까?

12. Pros

13. Pros : Java Interop

14. Pros : Lambda Expression
view.setOnClickListener(object : View.OnClickListener {
override fun onClick(view: View?) {
// do Something
}
})

15. Pros : Lambda Expression
view.setOnClickListener(object : View.OnClickListener {
override fun onClick(view: View?) {
// do Something
}
})

16. Pros : Lambda Expression
view.setOnClickListener(object : View.OnClickListener {
override fun onClick(view: View?) {
// do Something
}
})

17. Pros : Lambda Expression
view.setOnClickListener(object : View.OnClickListener {
override fun onClick(view: View?) {
// do Something
}
})

18. Pros : Lambda Expression
view.setOnClickListener(object : View.OnClickListener {
override fun onClick(view: View?) {
// do Something
}
})

19. Pros : Lambda Expression
view.setOnClickListener {
// do Something
}

20. Pros : ValidationCheck
• require
• requireNotNull
• check
• checkNotNull

21. Pros : ValidationCheck
if (-1L == b.getLong(GrimmOptions.KEY_CONTENT_ID, -1)) {
throw IllegalArgumentException("No content id exists")
}
if (null == b.getString(GrimmOptions.KEY_CONTENT_ALIAS)) {
throw IllegalArgumentException("No content alias exists")
}
if (!b.containsKey(GrimmOptions.KEY_CONTENT_IMAGES)) {
throw IllegalArgumentException("No KEY_CONTENT_IMAGES exists")
}
if (-1L == b.getLong(GrimmOptions.KEY_EPISODE_ID, -1)) {
throw IllegalArgumentException("No episode id exists")
}
if (!b.containsKey(GrimmOptions.KEY_EPISODE_IS_PURCHASED)) {
throw IllegalArgumentException("No episode purchase data")
}
if (-1L == b.getLong(GrimmOptions.KEY_EPISODE_LAST_UPDATE_TIME)) {
throw IllegalArgumentException("No episode last update time")
}
if (!b.containsKey(GrimmOptions.KEY_EPISODE_DIRECTION)) {
throw IllegalArgumentException("No KEY_EPISODE_DIRECTION exists")
}
if (!b.containsKey(GrimmOptions.KEY_EPISODE_URI)) {
throw IllegalArgumentException("No KEY_EPISODE_URI exists")
}

22. Pros : ValidationCheck
require(-1L == b.getLong(GrimmOptions.KEY_CONTENT_ID, -1), { "No content id exists" })
requireNotNull(b.getString(GrimmOptions.KEY_CONTENT_ALIAS), { "No content alias exists" })
require(!b.containsKey(GrimmOptions.KEY_CONTENT_IMAGES), { "No KEY_CONTENT_IMAGES exists" })
require(-1L == b.getLong(GrimmOptions.KEY_EPISODE_ID, -1), { "No episode id exists" })
require(!b.containsKey(GrimmOptions.KEY_EPISODE_IS_PURCHASED), { "No episode purchase data" })
require(-1L == b.getLong(GrimmOptions.KEY_EPISODE_LAST_UPDATE_TIME), { "No episode last update time" })
require(!b.containsKey(GrimmOptions.KEY_EPISODE_DIRECTION), { "No KEY_EPISODE_DIRECTION exists" })
require(!b.containsKey(GrimmOptions.KEY_EPISODE_URI), { "No KEY_EPISODE_URI exists" })

23. Pros : Higher order function
View Presenter
Event

24. Pros : Higher order function
View Presenter
Event
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
kotlinPresenter.someProcess(kotlinEvent)
}

25. Pros : Higher order function
View Presenter
UiUpdate
Event
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
kotlinPresenter.someProcess(kotlinEvent)
}

26. Pros : Higher order function
View Presenter
UiUpdate
Event
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
kotlinPresenter.someProcess(kotlinEvent)
}
fun someProcess(kotlinEvent: KotlinActivity.KotlinEvent) {
kotlinEvent.consume()
mvpView.showToast("Kotlin")
}

27. Pros : Higher order function
View Presenter
UiUpdate
Event
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
kotlinPresenter.someProcess(kotlinEvent)
}
fun someProcess(kotlinEvent: KotlinActivity.KotlinEvent) {
kotlinEvent.consume()
mvpView.showToast("Kotlin")
}
override fun showToast(msg: String) {
Toast.makeText(this, msg, Toast.LENGTH_SHORT).show()
}

28. Pros : Higher order function
View Presenter
Event
Action
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
kotlinPresenter.someProcess(kotlinEvent, { msg -> showToast(msg) })
}
override fun showToast(msg: String) {
Toast.makeText(this, msg, Toast.LENGTH_SHORT).show()
}

29. Pros : Higher order function
View Presenter
Consume
Action()
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
kotlinPresenter.someProcess(kotlinEvent, { msg -> showToast(msg) })
}
override fun showToast(msg: String) {
Toast.makeText(this, msg, Toast.LENGTH_SHORT).show()
}
Event
Action

30. Pros : Higher order function
View Presenter
Consume
Action()
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
kotlinPresenter.someProcess(kotlinEvent, { msg -> showToast(msg) })
}
override fun showToast(msg: String) {
Toast.makeText(this, msg, Toast.LENGTH_SHORT).show()
}
fun someProcess(kotlinEvent: KotlinActivity.KotlinEvent, action: (String) -> Unit) {
kotlinEvent.consume()
action("Kotlin")
}
Event
Action

31. Pros : Higher order function
products
.filter { it.badge.contains(item.badges ?: "_EMPTY_") }
.filter { it.pointPrice == 0 }
.map { it.coin }
.toList()

32. Pros : Kotlin Extension
fun Int.toStringMax99(): String = if (this > 99) {
"99+"
} else {
this.toString()
}

33. Pros : Kotlin Extension
var View.visible: Boolean
get() = this.visibility == View.VISIBLE
set(value) = if (value) {
this.visibility = View.VISIBLE
} else {
this.visibility = View.GONE
}

34. Pros : Android Extension
• findViewById 지옥 에서 탈출

35. Pros : Android Extension
• findViewById 지옥 에서 탈출
textView = findViewById(R.id.tv_kotlin_activity)
textView2 = findViewById(R.id.tv_kotlin_activity2)
textView3 = findViewById(R.id.tv_kotlin_activity3)
imageView = findViewById(R.id.iv_kotlin_activity)
imageView2 = findViewById(R.id.iv_kotlin_activity2)
imageView3 = findViewById(R.id.iv_kotlin_activity3)
textView.text = "text1"
textView2.text = "text2"
textView3.text = "text3"
imageView.setImageResource(R.drawable.ic_photo_normal)
imageView2.setImageResource(R.drawable.ic_photo_normal)
imageView3.setImageResource(R.drawable.ic_photo_normal)

36. Pros : Android Extension
• findViewById 지옥 에서 탈출
textView = findViewById(R.id.tv_kotlin_activity)
textView2 = findViewById(R.id.tv_kotlin_activity2)
textView3 = findViewById(R.id.tv_kotlin_activity3)
imageView = findViewById(R.id.iv_kotlin_activity)
imageView2 = findViewById(R.id.iv_kotlin_activity2)
imageView3 = findViewById(R.id.iv_kotlin_activity3)
textView.text = "text1"
textView2.text = "text2"
textView3.text = "text3"
imageView.setImageResource(R.drawable.ic_photo_normal)
imageView2.setImageResource(R.drawable.ic_photo_normal)
imageView3.setImageResource(R.drawable.ic_photo_normal)

37. Pros : Android Extension
• findViewById 지옥 에서 탈출
import kotlinx.android.synthetic.main.kotlin_activity.*
tv_kotlin_activity.text = "text1"
tv_kotlin_activity2.text = "text2"
tv_kotlin_activity3.text = "text3"
iv_kotlin_activity.setImageResource(R.drawable.ic_photo_normal)
iv_kotlin_activity2.setImageResource(R.drawable.ic_photo_normal)
iv_kotlin_activity3.setImageResource(R.drawable.ic_photo_normal)

38. Pros : Lazy Evaluation
• lateInit
• Dependency Injection (Dagger)

39. Pros : Lazy Evaluation
• lateInit
• Dependency Injection (Dagger)
• runtime 에 set 되는 mutable property (var)

40. Pros : Lazy Evaluation
• lateInit
• Dependency Injection (Dagger)
• runtime 에 set 되는 mutable property (var)
• by lazy
• runtime에 set되는 read-only property (val)

41. Pros : Lazy Evaluation
• lateInit
• Dependency Injection (Dagger)
• runtime 에 set 되는 mutable property (var)
• by lazy
• runtime에 set되는 read-only property (val)
• 리소스가 많이 들거나 연산이 오래 걸리지만 자주 사용
하는 property

42. Pros : Lazy Evaluation
private val pdPending by lazy { ... }
private val presentAdapter by lazy {
...
}
lateinit @Inject var locale: LezhinLocale
lateinit @Inject var userApi: UserApi
lateinit @Inject var presenter: PresentBoxMvpPresenter

43. Pros : JoinToString
val sb = StringBuilder()
val size = items.size
for (i in 0..size - 1) {
sb.append(items[i].id)
if (i < size - 1) {
sb.append(‘, ')
}
} // item1, item2, item3..
item1
item2
item3
…

44. Pros : JoinToString
val sb = StringBuilder()
val size = items.size
for (i in 0..size - 1) {
sb.append(items[i].id)
if (i < size - 1) {
sb.append(‘, ')
}
} // item1, item2, item3..
items.joinToString(separator = “, ”)
// item1, item2, item3..
item1
item2
item3
…

45. Pros : Collection Api
• Rx를 사용해 iterable을 사용 할 필요가 없음.

46. Pros : Collection Api
• Rx를 사용해 iterable을 사용 할 필요가 없음.
• Higher order function 사용을 통해 가독성, 생산성 향상.

47. Pros : Collection Api
Observable.fromIterable(products)
.filter { it.badge.contains(item.badges ?: "_EMPTY_") }
.filter { it.pointPrice == 0 }

48. Pros : Collection Api
Observable.fromIterable(products)
.filter { it.badge.contains(item.badges ?: "_EMPTY_") }
.filter { it.pointPrice == 0 }

49. Pros : Collection Api
products
.filter { it.badge.contains(item.badges ?: "_EMPTY_") }
.filter { it.pointPrice == 0 }

50. Pros : Readability, Productivity
val margin = TypedValue.applyDimension(
TypedValue.COMPLEX_UNIT_DIP, 24f, resources.displayMetrics).toInt()
val lp = CoordinatorLayout.LayoutParams(
ViewGroup.LayoutParams.WRAP_CONTENT, ViewGroup.LayoutParams.WRAP_CONTENT)
lp.anchorId = R.id.rv_activity_main
lp.anchorGravity = Gravity.RIGHT or GravityCompat.END or Gravity.BOTTOM
lp.rightMargin = margin
lp.bottomMargin = margin
cl_activity_main.addView(button, lp)

51. Pros : Readability, Productivity
val margin = TypedValue.applyDimension(
TypedValue.COMPLEX_UNIT_DIP, 24f, resources.displayMetrics).toInt()
val lp = CoordinatorLayout.LayoutParams(
ViewGroup.LayoutParams.WRAP_CONTENT, ViewGroup.LayoutParams.WRAP_CONTENT).apply {
anchorId = R.id.rv_activity_main
anchorGravity = Gravity.RIGHT or GravityCompat.END or Gravity.BOTTOM
rightMargin = margin
bottomMargin = margin
}
cl_activity_main.addView(button, lp)

52. Pros : Readability, Productivity
presenter.attachView(this@PresentBoxActivity)
presenter.loadBalance(token, userId)
presenter.loadItems(token, userId)

53. Pros : Readability, Productivity
presenter.attachView(this@PresentBoxActivity)
presenter.loadBalance(token, userId)
presenter.loadItems(token, userId)
with(presenter) {
attachView(this@PresentBoxActivity)
loadBalance(token, userId)
loadItems(token, userId)
}

54. Pros : Readability, Productivity
if (null != episode.topNotice) {
add(0, episode.topNotice.toContentImage(BuildConfig.CDN_HOST))
}

55. Pros : Readability, Productivity
episode.topNotice?.let {
add(0, it.toContentImage(BuildConfig.CDN_HOST))
}

56. Pros : Readability, Productivity
if(null != playerGroupPool[group]){
if(null != playerGroupPool[group]!![id]){
val palyerData = playerGroupPool[group]!![id]!!
palyerData.player.playWhenReady = false
palyerData.isRunning = false
}
}

57. Pros : Readability, Productivity
playerGroupPool[group]?.get(id)?.let {
with(it){
player.playWhenReady = false
isRunning = false
}
}

58. Pros : Readability, Productivity
playerGroupPool[group]?.get(id)?.run {
player.playWhenReady = false
isRunning = false
}

59. Pros : Readability, Productivity
override fun getItemViewType(position: Int): Int {
return when (position) {
items.size -> TYPE_FOOTER
else -> TYPE_ITEM
}
}
override fun getItemCount(): Int {
return items.size + 1
}

60. Pros : Readability, Productivity
override fun getItemViewType(position: Int): Int {
return when (position) {
items.size -> TYPE_FOOTER
else -> TYPE_ITEM
}
}
override fun getItemCount(): Int {
return items.size + 1
}

61. Pros : Readability, Productivity
override fun getItemViewType(position: Int): Int = when (position) {
items.size -> TYPE_FOOTER
else -> TYPE_ITEM
}
override fun getItemCount(): Int = items.size + 1

62. Pros : Confidence

63. Pros : FP
Kotlin FP

64. Pros : FP
Kotlin FP
FunFunStudy
gitHub : https://github.com/funfunStudy/study/wiki
facebook : https://www.facebook.com/groups/1189616354467814/?ref=bookmarks

65. Problems

66. Problem : 잘 사용 하고 있나??

67. Problem : kapt

68. Problem : FP 선무당..

69. Problem : Code Artist?

70. Problem : 개발자 구하기가…

72. Tips : Toy Project

73. Tips : Study

74. Tips : CodeReview

75. Tips : CodeReview
0
25
50
75
100
125
Time
Performance
2~3M

76. Tips : Progressive

77. Tips : Progressive
Business logicData UI

78. Tips : Progressive
리펙토링새로운 코드 작성
기존 코드를 수정
할 때

79. Tips : KtLint
https://github.com/shyiko/ktlint
configurations {
ktlint
}
dependencies {
ktlint 'com.github.shyiko:ktlint:0.9.0'
}
task ktlint(type: JavaExec) {
……
}
task ktlintFormat(type: JavaExec) {
……
}
afterEvaluate { project ->
check.dependsOn ktlint
}

80. Links
https://medium.com/@lazysoul
https://github.com/funfunStudy/study/wiki
https://www.facebook.com/groups/1189616354467814
http://tech.lezhin.com/
https://www.slideshare.net/myeonginwoo