1年半プロジェクトでKotlinを使ってみて良かったこと、良くなかったこと(2017-01 CA.apk)

1年半プロジェクトでKotlinを使ってみて
良かったこと、良くなかったこと
CA.apk

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About me
@_a_akira
AAkira
CyberAgent, Inc.
Akira Aratani

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About FRESH!
• 生放送配信プラットフォーム
• FRESH! ≒ AbemaTV

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Released map
M1 2012-04-12
M11 2015-03-19
M14 2015-10-01
1.0-beta4 2015-12-22
M13 2015-09-16
1.0 2016-02-16
1.0-RC 2016-02-04
2016-01-21 Release
2015-04 開発開始
kotlin
FRESH

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良かったこと

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コード量が減る

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for (int i = 0; i < 10; i++) {
Log.v("tag", "i=" + i);
}
int[] array = {0, 10, 20, 30, 40, 50, 60};
for (int item : array) {
Log.v("tag", "item=" + item);
}
for (int i = 0; i < array.length; i++) {
Log.v("tag", "item[" + i + "]=" + array[i]);
}

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convert to Kotlin
for (i in 0..9) { Log.v("tag", "i=" + i) }
val array = intArrayOf(0, 10, 20, 30, 40, 50, 60)
array.forEach { Log.v("tag", "item=" + it) }
array.forEachIndexed { index, item ->
Log.v("tag", "item[$index]=$item")
}

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Everything is stream
https://speakerdeck.com/aakira/ﬂux-with-kotlin-abema-dev-con-2016

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Observable.from(new Integer[]{1, 2, 3, 4, 5, 6, 7, 8, 9, 10})
.filter(new Func1() {
@Override
public Boolean call(Integer i) {
return (i % 2) == 0;
}
})
.map(new Func1() {
@Override
public Integer call(Integer i) {
return i * 10;
}
})
.subscribe(new Observer() {
@Override
public void onNext(Integer integer) {
Log.d("TAG", integer.toString());
}
@Override
public void onCompleted() {
}
@Override
public void onError(Throwable e) {
}
});

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Observable.from(new Integer[]{1, 2, 3, 4, 5, 6, 7, 8, 9, 10})
.filter(new Func1() {
@Override
public Boolean call(Integer i) {
return (i % 2) == 0;
}
})
.map(new Func1() {
@Override
public Integer call(Integer i) {
return i * 10;
}
})
.subscribe(new Observer() {
@Override
public void onNext(Integer integer) {
Log.d("TAG", integer.toString());
}
@Override
public void onCompleted() {
}
@Override
public void onError(Throwable e) {
}
});
20, 40, 60, 80, 100

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convert to Kotlin
Observable.from(arrayOf(1, 2, 3, 4, 5, 6, 7, 8, 9, 10))
.filter { i -> i % 2 == 0 }
.map { i -> i * 10 }
.subscribe(object : Observer {
override fun onNext(integer: Int?) {
Log.d("TAG", integer.toString())
}
override fun onCompleted() {}
override fun onError(e: Throwable) {}
})

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.filter { it % 2 == 0 }
.map { it * 10 }
.subscribe(object : Observer {
override fun onNext(integer: Int?) {
Log.d("TAG", integer.toString())
}
override fun onCompleted() {}
override fun onError(e: Throwable) {}
})

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.filter { it % 2 == 0 }
.map { it * 10 }
.subscribe({
Log.d("TAG", it.toString())
}, {
// onError
}, {
// onCompleted
})

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拡張関数便利

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拡張関数便利
forEachの正体もこれ
/**
* Performs the given [action] on each element, providing sequential index with the
element.
* @param [action] function that takes the index of an element and the element itself
* and performs the desired action on the element.
*/
public inline fun Iterable.forEachIndexed(action: (Int, T) -> Unit): Unit {
var index = 0
for (item in this) action(index++, item)
}
/**
* Performs the given [action] on each element.
*/
@kotlin.internal.HidesMembers
public inline fun Iterable.forEach(action: (T) -> Unit): Unit {
for (element in this) action(element)
}

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拡張関数便利
• run
• let
• apply
• (with)
Standard.kt

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拡張関数便利
run, let, apply, withの使用回数

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拡張関数便利
• run
• let
• apply
• (with)
146 箇所

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拡張関数便利
• run
• let
• apply
• (with)
146 箇所
442 箇所

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拡張関数便利
• run
• let
• apply
• (with)
146 箇所
442 箇所
293 箇所

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拡張関数便利
• run
• let
• apply
• (with)
146 箇所
442 箇所
293 箇所
0 箇所

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拡張関数便利
FRESH!内で定義されている
拡張関数の数

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拡張関数便利
58 個
fun\s[A-z]*\.[a-z]*$.*$\s\{

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Swiftなんとなくわかる

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iOSの方が優先されがち
→ 先に実装終わってる
この仕様どうしよう?

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iOSのコードパクろう

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コードの意図が伝わる

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師匠 < コードは小説だ

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val hoge = 10
var foo = 100
val bar: String
if (hoge > 5) {
foo = 200
bar = “fresh!"
} else {
foo = 300
bar = "abema"
}
Log.v("TAG", "foo=$foo, bar=$bar")

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val hoge = 10
var foo = 100
val bar: String
if (hoge > 5) {
foo = 200
bar = “fresh!"
} else {
foo = 300
bar = "abema"
}
Log.v("TAG", "foo=$foo, bar=$bar")
定数が一目瞭然

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class HogeActivity : Activity {
companion object {
private const val EXTRA_HOGE = "extra_hoge"
private const val EXTRA_FOO = "extra_foo"
private const val EXTRA_BAR = "extra_bar"
fun createIntent(activity: Activity, hoge: Int) =
Intent(activity, HogeActivity::class.java).apply {
putExtra(EXTRA_HOGE, hoge)
}
fun createIntent(activity: Activity, foo: String, bar: String? = null) =
putExtra(EXTRA_FOO, foo)
putExtra(EXTRA_BAR, bar)
}
}
……
}

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class HogeActivity : Activity {
companion object {
private const val EXTRA_HOGE = "extra_hoge"
private const val EXTRA_FOO = "extra_foo"
private const val EXTRA_BAR = "extra_bar"
fun createIntent(activity: Activity, hoge: Int) =
putExtra(EXTRA_HOGE, hoge)
}
fun createIntent(activity: Activity, foo: String, bar: String? = null) =
putExtra(EXTRA_FOO, foo)
putExtra(EXTRA_BAR, bar)
}
}
……
} nullに意味がある

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アプリがcrashしない

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Androidのcrash ranking
https://www.apteligent.com/developer-resources/top-5-crashes-on-android/
1. java.lang.NullPointerException
2. java.lang.OutOfMemoryError
3. android.view.WindowManager.BadTokenException
4. java.lang.IllegalException
5. android.database.sqlite.SQLiteException

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var hoge: String? = “hoge"
// ΋͠hoge͕nullͩͬͨΒ0
if (hoge?.length ?: 0 > 0) hoge = "replace"
// ΋͠hoge͕nullͩͬͨΒॳظԽ
hoge = hoge ?: "init"

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class Hoge {
var onHogeChangedListener: (() -> Unit)? = null
fun doSomething() {
onHogeChangedListener?.invoke()
}
}
class HogeActivity: Activity() {
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
val hoge = Hoge()
hoge.onHogeChangedListener = {
}
}
}

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良くなかったこと

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ない

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強いて言うなら…

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メソッド数が微妙に増える

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メソッド数が微妙に増える
5142 kotlin 
2 kotlin._Assertions 
12 kotlin.annotation 
2519 kotlin.collections 
65 kotlin.comparisons 
31 kotlin.concurrent 
6 kotlin.internal 
296 kotlin.io 
549 kotlin.jvm 
24 kotlin.jvm.functions 
506 kotlin.jvm.internal 
2 kotlin.jvm.internal.unsafe 
23 kotlin.properties 
227 kotlin.ranges 
61 kotlin.reﬂect 
423 kotlin.sequences 
3 kotlin.system 
762 kotlin.text
https://github.com/KeepSafe/dexcount-gradle-plugin
Kotlin version : 1.06

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動作が不安定(だった)

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動作が不安定(だった)
Kotlin 86.5%
Java 13.4%
Other 0.1%

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人材の流動性

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人材の流動性
< Kotlinだからなぁ〜
ɹ FRESHに来てください！
(実話)

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人材の流動性
< Welcome!!
ɹ Kotlin書きたい！
(実話)

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まとめ

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まとめ
メリットの方が多いので
Kotlinで開発した方が良い

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でしょうね

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何が言いたいか

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まとめ
Kotlin

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まとめ
Kotlin
RxJava

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まとめ
Dagger
Kotlin
RxJava

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まとめ
好きなLibraryなんでも
Dagger
Kotlin
RxJava

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まとめ
Androidエンジニアを募集しております
&

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まだ時間ある…？

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時間あったらおまけ

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よく使ってる拡張関数

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Animator Listener
fun Animator.setListener(
onAnimationStart: (Animator) -> Unit = {},
onAnimationEnd: (Animator) -> Unit = {},
onAnimationCancel: (Animator) -> Unit = {},
onAnimationRepeat: (Animator) -> Unit = {}
) = apply {
addListener(object : Animator.AnimatorListener {
override fun onAnimationStart(animation: Animator) {
onAnimationStart(animation)
}
override fun onAnimationEnd(animation: Animator) {
onAnimationEnd(animation)
}
override fun onAnimationCancel(animation: Animator) {
onAnimationCancel(animation)
}
override fun onAnimationRepeat(animation: Animator) {
onAnimationRepeat(animation)
}
})
}

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Animator Listener
ObjectAnimator.ofFloat(this, "alpha", 1.0, 0.0)
.setDuration(300)
.setListener(onAnimationStart = { backgroundView.toVisible() })
.start()

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Visibility
fun View.toVisible() {
visibility = View.VISIBLE
}
fun View.toInvisible() {
visibility = View.INVISIBLE
}
fun View.toGone() {
visibility = View.GONE
}

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Visibility
view.toGone()

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Apply margin
fun View.applyMargin(left: Int = 0, top: Int = 0,
right: Int = 0, bottom: Int = 0) =
(layoutParams as ViewGroup.MarginLayoutParams).apply {
leftMargin = left
topMargin = top
rightMargin = right
bottomMargin = bottom
}

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Apply margin
view.applyMargin(top = 16, right = 48)

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1年半プロジェクトでKotlinを使ってみて良かったこと、良くなかったこと(2017-01 CA.apk)

1年半プロジェクトでKotlinを使ってみて良かったこと、良くなかったこと(2017-01 CA.apk)

AAkira

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