Android KTX (Google IO 2018)

This talk introduces Android KTX, which is the new set of Kotlin extensions for Android. It demonstrates how Android developers writing Kotlin can use Android KTX to make their code more idiomatic, concise, and pleasant. It will also discuss how developers can make their own libraries more Kotlin-friendly.

Video: https://youtu.be/st1XVfkDWqk

Transcript

1. Android KTX Jake Wharton
2. Android KTX Jake Wharton
3. val userLayout: ViewGroup = findViewById(R.id.users) for (index in 0 until userLayout.childCount) { val view = userLayout.getChildAt(index) // Do something with index and view… }
4. fun ViewGroup.forEachIndexed(action: (Int, View) -> Unit) { for (index in 0 until childCount) { action(index, getChildAt(index)) }Z } val userLayout: ViewGroup = findViewById(R.id.users) for (index in 0 until userLayout.childCount) { val view = userLayout.getChildAt(index) // Do something with index and view… }A
5. fun ViewGroup.forEachIndexed(action: (Int, View) -> Unit) { for (index in 0 until childCount) { action(index, getChildAt(index)) }Z } val userLayout: ViewGroup = findViewById(R.id.users) for (index in 0 until userLayout.childCount) { val view = userLayout.getChildAt(index) // Do something with index and view… }A
6. fun ViewGroup.forEachIndexed(action: (Int, View) -> Unit) { for (index in 0 until childCount) { action(index, getChildAt(index)) }Z }D val userLayout: ViewGroup = findViewById(R.id.users) for (index in 0 until userLayout.childCount) {G val view = userLayout.getChildAt(index) // Do something with index and view… }A
7. fun ViewGroup.forEachIndexed(action: (Int, View) -> Unit) { for (index in 0 until childCount) { action(index, getChildAt(index)) }Z }D val userLayout: ViewGroup = findViewById(R.id.users) userLayout.forEachIndexed {Gindex, view -> // Do something with index and view… }A for ( in 0 until .childCount) val = userLayout.getChildAt(index)
8. fun ViewGroup.forEachIndexed(action: (Int, View) -> Unit) { for (index in 0 until childCount) { action(index, getChildAt(index)) }Z }D val userLayout: ViewGroup = findViewById(R.id.users) userLayout.forEachIndexed {Gindex, view -> // Do something with index and view… }A
9. fun ViewGroup.forEachIndexed(action: (Int, View) -> Unit) { for (index in 0 until childCount) { action(index, getChildAt(index)) }Z }D val userLayout: ViewGroup = findViewById(R.id.users) userLayout.forEachIndexed {Gindex, view -> // Do something with index and view… }A
10. inline fun ViewGroup.forEachIndexed(action: (Int, View) -> Unit) { for (index in 0 until childCount) { action(index, getChildAt(index)) }Z }D val userLayout: ViewGroup = findViewById(R.id.users) userLayout.forEachIndexed {Gindex, view -> // Do something with index and view… }A
11. inline fun ViewGroup.forEachIndexed(action: (Int, View) -> Unit) { for (index in 0 until childCount) { action(index, getChildAt(index)) }Z }D val userLayout: ViewGroup = findViewById(R.id.users) userLayout.forEachIndexed {Gindex, view -> // Do something with index and view… }A
12. // In an Activity, on API 23+… val notifications = getSystemService(NotificationManager::class.java)
13. // In an Activity, on API 23+… val notifications = getSystemService(NotificationManager::class.java) // or all API levels… val notifications = ContextCompat.getSystemService(this, NotificationManager::class.java)
14. // In an Activity, on API 23+… val notifications = getSystemService(NotificationManager::class.java) // or all API levels… val notifications = ContextCompat.getSystemService(this, NotificationManager::class.java) inline fun <reified T> Context.systemService() = ContextCompat.getSystemService(this, T::class.java)
15. inline fun <reified T> Context.systemService() = ContextCompat.getSystemService(this, T::class.java) // In an Activity, on API 23+… val notifications = getSystemService(NotificationManager::class.java) // or all API levels… val notifications = ContextCompat.getSystemService(this, NotificationManager::class.java)
16. inline fun <reified T> Context.systemService() = ContextCompat.getSystemService(this, T::class.java) // In an Activity, on API 23+… val notifications = getSystemService(NotificationManager::class.java) // or all API levels… val notifications = ContextCompat.getSystemService(this, NotificationManager::class.java)
17. inline fun <reified T> Context.systemService() = ContextCompat.getSystemService(this, T::class.java) // In an Activity, on API 23+… val notifications = getSystemService(NotificationManager::class.java)H // or all API levels… val notifications = ContextCompat.getSystemService(this, NotificationManager::class.java) s
18. inline fun <reified T> Context.systemService() = ContextCompat.getSystemService(this, T::class.java) // In an Activity… val notifications = systemService<NotificationManager>()H S
19. inline fun <reified T> Context.systemService() = ContextCompat.getSystemService(this, T::class.java) // In an Activity… val notifications = systemService<NotificationManager>()H
20. avatarView.setPadding( 10, avatarView.paddingTop, 10, avatarView.paddingBottom)
21. inline fun View.updatePadding( left: Int = paddingLeft, top: Int = paddingTop, right: Int = paddingRight, bottom: Int = paddingBottom ) { setPadding(left, top, right, bottom) } avatarView.setPadding( 10, avatarView.paddingTop, 10, avatarView.paddingBottom)
22. inline fun View.updatePadding( left: Int = paddingLeft, top: Int = paddingTop, right: Int = paddingRight, bottom: Int = paddingBottom ) { setPadding(left, top, right, bottom) } avatarView.setPadding( 10, avatarView.paddingTop, 10, avatarView.paddingBottom)
23. inline fun View.updatePadding( left: Int = paddingLeft, top: Int = paddingTop, right: Int = paddingRight, bottom: Int = paddingBottom ) { setPadding(left, top, right, bottom) }A avatarView.setPadding( 10, avatarView.paddingTop, 10, avatarView.paddingBottom)R update
24. inline fun View.updatePadding( left: Int = paddingLeft, top: Int = paddingTop, right: Int = paddingRight, bottom: Int = paddingBottom ) { setPadding(left, top, right, bottom) }A avatarView.updatePadding(10, 10)R
25. inline fun View.updatePadding( left: Int = paddingLeft, top: Int = paddingTop, right: Int = paddingRight, bottom: Int = paddingBottom ) { setPadding(left, top, right, bottom) }A avatarView.updatePadding(10, 10)R
26. inline fun View.updatePadding( left: Int = paddingLeft, top: Int = paddingTop, right: Int = paddingRight, bottom: Int = paddingBottom ) { setPadding(left, top, right, bottom) }A avatarView.updatePadding(left = 10, right = 10)R
27. inline fun View.updatePadding( left: Int = paddingLeft, top: Int = paddingTop, right: Int = paddingRight, bottom: Int = paddingBottom ) { setPadding(left, top, right, bottom) }A avatarView.updatePadding(left = 10, right = 10)R
28. val rect = avatarView.clipBounds val left = rect.left val top = rect.top val right = rect.right val bottom = rect.bottom // Use left, top, right, bottom…
29. val rect = avatarView.clipBounds val left = rect.left val top = rect.top val right = rect.right val bottom = rect.bottom // Use left, top, right, bottom… inline operator fun Rect.component1() = left inline operator fun Rect.component2() = top inline operator fun Rect.component3() = right inline operator fun Rect.component4() = bottom
30. inline operator fun Rect.component1() = left inline operator fun Rect.component2() = top inline operator fun Rect.component3() = right inline operator fun Rect.component4() = bottom val rect = avatarView.clipBounds val left = rect.left val top = rect.top val right = rect.right val bottom = rect.bottom // Use left, top, right, bottom…
31. inline operator fun Rect.component1() = left inline operator fun Rect.component2() = top inline operator fun Rect.component3() = right inline operator fun Rect.component4() = bottom val rect = avatarView.clipBounds val left = rect.left val top = rect.top val right = rect.right val bottom = rect.bottom // Use left, top, right, bottom…
32. inline operator fun Rect.component1() = left inline operator fun Rect.component2() = top inline operator fun Rect.component3() = right inline operator fun Rect.component4() = bottom val rect = avatarView.clipBounds val left = rect.left valTtop = rect.top valRright = rect.right valBbottom = rect.bottom // Use left, top, right, bottom…
33. inline operator fun Rect.component1() = left inline operator fun Rect.component2() = top inline operator fun Rect.component3() = right inline operator fun Rect.component4() = bottom val (left,Ttop,Rright,Bbottom) = avatarView.clipBounds // Use left, top, right, bottom…
34. inline operator fun Rect.component1() = left inline operator fun Rect.component2() = top inline operator fun Rect.component3() = right inline operator fun Rect.component4() = bottom val (left,Ttop,Rright) = avatarView.clipBounds // Use left, top, right…
35. inline operator fun Rect.component1() = left inline operator fun Rect.component2() = top inline operator fun Rect.component3() = right inline operator fun Rect.component4() = bottom val (left,T_,Rright) = avatarView.clipBounds // Use left, right…
36. inline operator fun Rect.component1() = left inline operator fun Rect.component2() = top inline operator fun Rect.component3() = right inline operator fun Rect.component4() = bottom val (left,T_,Rright) = avatarView.clipBounds // Use left, right…
37. var onlyDigits = true for (c in phoneNumber) {A if (!c.isDigit()) { onlyDigits = false break }G }B
38. r true for (c in ) if (!c. ) { onlyDigits = false break }G val onlyDigits = phoneNumber.all {Ait.isDigit() }B
39. .all {Ait.isDigit() }B val onlyDigits = TextUtils.isDigitsOnly(phoneNumber)
40. inline fun CharSequence.isDigitsOnly() = TextUtils.isDigitsOnly(this)Z val onlyDigits = TextUtils.isDigitsOnly(phoneNumber)L
41. inline fun CharSequence.isDigitsOnly() = TextUtils.isDigitsOnly(this)Z val onlyDigits = phoneNumber.isDigitsOnly()L
42. inline fun CharSequence.isDigitsOnly() = TextUtils.isDigitsOnly(this)Z val onlyDigits = phoneNumber.
43. inline fun CharSequence.isDigitsOnly() = TextUtils.isDigitsOnly(this)Z val onlyDigits = phoneNumber.
44. inline fun CharSequence.isDigitsOnly() = TextUtils.isDigitsOnly(this)Z val onlyDigits = phoneNumber.is
45. inline fun CharSequence.isDigitsOnly() = TextUtils.isDigitsOnly(this)Z val onlyDigits = phoneNumber.is
46. inline fun CharSequence.isDigitsOnly() = TextUtils.isDigitsOnly(this)Z val onlyDigits = phoneNumber.isDigitsOnly()L
47. inline fun ViewGroup.forEachIndexed(action: (Int, View) -> Unit) { for (index in 0 until childCount) { action(index, getChildAt(index)) }Z } inline fun <reified T> Context.systemService() = ContextCompat.getSystemService(this, T::class.java) inline fun View.updatePadding( left: Int = paddingLeft, top: Int = paddingTop, right: Int = paddingRight, bottom: Int = paddingBottom ) { setPadding(left, top, right, bottom) } inline operator fun Rect.component1() = left inline operator fun Rect.component2() = top inline operator fun Rect.component3() = right inline operator fun Rect.component4() = bottom inline fun CharSequence.isDigitsOnly() = TextUtils.isDigitsOnly(this)Z
49. core-ktx Android KTX
50. Android KTX core-ktx Android framework
51. Android KTX Android framework support-compat core-ktx
52. Android KTX Android framework core core-ktx
53. Android KTX Android framework core core-ktx fragment-ktx fragment palette-ktx palette collection-ktx collection lifecycle-reactivestreams-ktx lifecycle-reactivestreams sqlite-ktx sqlite navigation-*-ktx navigation-* work-runtime-ktx work-runtime
54. Android KTX Android framework core core-ktx fragment-ktx fragment palette-ktx palette collection-ktx collection lifecycle-reactivestreams-ktx lifecycle-reactivestreams sqlite-ktx sqlite navigation-*-ktx navigation-* work-runtime-ktx work-runtime
55. @RequiresApi(26) operator fun Color.plus(c: Color): Color { val s = if (colorSpace != c.colorSpace) c.convert(colorSpace) else c val src = s.components val dst = components var sa = s.alpha() // Destination alpha pre-composited var da = alpha() * (1.0f - sa) // Index of the alpha component val ai = componentCount - 1 // Final alpha: src_alpha + dst_alpha * (1 - src_alpha) dst[ai] = sa + da // Divide by final alpha to return non pre-multiplied color if (dst[ai] > 0) { sa /= dst[ai] da /= dst[ai] } // Composite non-alpha components for (i in 0 until ai) { dst[i] = src[i] * sa + dst[i] * da } return Color.valueOf(dst, colorSpace) }
56. @RequiresApi(26) operator fun Color.plus(c: Color): Color { val s = if (colorSpace != c.colorSpace) c.convert(colorSpace) else c val src = s.components val dst = components var sa = s.alpha() // Destination alpha pre-composited var da = alpha() * (1.0f - sa) // Index of the alpha component val ai = componentCount - 1 // Final alpha: src_alpha + dst_alpha * (1 - src_alpha) dst[ai] = sa + da // Divide by final alpha to return non pre-multiplied color if (dst[ai] > 0) { sa /= dst[ai] da /= dst[ai] } // Composite non-alpha components for (i in 0 until ai) { dst[i] = src[i] * sa + dst[i] * da } return Color.valueOf(dst, colorSpace) }
57. @RequiresApi(26) operator fun Color.plus(c: Color): Color { val s = if (colorSpace != c.colorSpace) c.convert(colorSpace) else c val src = s.components val dst = components var sa = s.alpha() // Destination alpha pre-composited var da = alpha() * (1.0f - sa) // Index of the alpha component val ai = componentCount - 1 // Final alpha: src_alpha + dst_alpha * (1 - src_alpha) dst[ai] = sa + da // Divide by final alpha to return non pre-multiplied color if (dst[ai] > 0) { sa /= dst[ai] da /= dst[ai] } // Composite non-alpha components for (i in 0 until ai) { dst[i] = src[i] * sa + dst[i] * da } return Color.valueOf(dst, colorSpace) }
58. public final class ColorUtils { }Z
59. public final class ColorUtils { @ColorInt public static int compositeColors( @ColorInt int foreground, @ColorInt int background) { // … }X }Z
60. public final class ColorUtils { @ColorInt public static int compositeColors( @ColorInt int foreground, @ColorInt int background) { // … }X @RequiresApi(26) public static Color compositeColors( Color foreground, Color background) { // … }Y }Z
61. @RequiresApi(26) operator fun Color.plus(c: Color): Color { val s = if (colorSpace != c.colorSpace) c.convert(colorSpace) else c val src = s.components val dst = components var sa = s.alpha() // Destination alpha pre-composited var da = alpha() * (1.0f - sa) // Index of the alpha component val ai = componentCount - 1 // Final alpha: src_alpha + dst_alpha * (1 - src_alpha) dst[ai] = sa + da // Divide by final alpha to return non pre-multiplied color if (dst[ai] > 0) { sa /= dst[ai] da /= dst[ai] } // Composite non-alpha components for (i in 0 until ai) { dst[i] = src[i] * sa + dst[i] * da } return Color.valueOf(dst, colorSpace) }
62. @RequiresApi(26) inline operator fun Color.plus(c: Color): Color = ColorUtils.compositeColors(c, this)
63. inline fun ViewGroup.forEachIndexed(action: (Int, View) -> Unit) { for (index in 0 until childCount) { action(index, getChildAt(index)) }Z } inline fun <reified T> Context.systemService() = ContextCompat.getSystemService(this, T::class.java) inline fun View.updatePadding( left: Int = paddingLeft, top: Int = paddingTop, right: Int = paddingRight, bottom: Int = paddingBottom ) { setPadding(left, top, right, bottom) } inline operator fun Rect.component1() = left inline operator fun Rect.component2() = top inline operator fun Rect.component3() = right inline operator fun Rect.component4() = bottom inline fun CharSequence.isDigitsOnly() = TextUtils.isDigitsOnly(this)Z
64. inline fun ViewGroup.forEachIndexed(action: (Int, View) -> Unit) { for (index in 0 until childCount) { action(index, getChildAt(index)) }Z } inline fun <reified T> Context.systemService() = ContextCompat.getSystemService(this, T::class.java) inline fun View.updatePadding( left: Int = paddingLeft, top: Int = paddingTop, right: Int = paddingRight, bottom: Int = paddingBottom ) { setPadding(left, top, right, bottom) } inline operator fun Rect.component1() = left inline operator fun Rect.component2() = top inline operator fun Rect.component3() = right inline operator fun Rect.component4() = bottom inline fun CharSequence.isDigitsOnly() = TextUtils.isDigitsOnly(this)Z
65. KTX Principles
66. KTX Principles Adapt existing functionality and redirect features upstream
67. inline fun ViewGroup.forEachIndexed(action: (Int, View) -> Unit) { for (index in 0 until childCount) { action(index, getChildAt(index)) }Z } inline fun <reified T> Context.systemService() = ContextCompat.getSystemService(this, T::class.java) inline fun View.updatePadding( left: Int = paddingLeft, top: Int = paddingTop, right: Int = paddingRight, bottom: Int = paddingBottom ) { setPadding(left, top, right, bottom) } inline operator fun Rect.component1() = left inline operator fun Rect.component2() = top inline operator fun Rect.component3() = right inline operator fun Rect.component4() = bottom inline fun CharSequence.isDigitsOnly() = TextUtils.isDigitsOnly(this)Z
68. inline fun ViewGroup.forEachIndexed(action: (Int, View) -> Unit) { for (index in 0 until childCount) { action(index, getChildAt(index)) }Z } inline fun <reified T> Context.systemService() = ContextCompat.getSystemService(this, T::class.java) inline fun View.updatePadding( left: Int = paddingLeft, top: Int = paddingTop, right: Int = paddingRight, bottom: Int = paddingBottom ) { setPadding(left, top, right, bottom) } inline operator fun Rect.component1() = left inline operator fun Rect.component2() = top inline operator fun Rect.component3() = right inline operator fun Rect.component4() = bottom inline fun CharSequence.isDigitsOnly() = TextUtils.isDigitsOnly(this)Z
69. inline fun ViewGroup.forEachIndexed(action: (Int, View) -> Unit) { for (index in 0 until childCount) { action(index, getChildAt(index)) }Z } inline fun <reified T> Context.systemService() = ContextCompat.getSystemService(this, T::class.java) inline fun View.updatePadding( left: Int = paddingLeft, top: Int = paddingTop, right: Int = paddingRight, bottom: Int = paddingBottom ) { setPadding(left, top, right, bottom) } inline operator fun Rect.component1() = left inline operator fun Rect.component2() = top inline operator fun Rect.component3() = right inline operator fun Rect.component4() = bottom inline fun CharSequence.isDigitsOnly() = TextUtils.isDigitsOnly(this)Z
70. operator fun ViewGroup.iterator() = object : MutableIterator<View> { private var index = 0 override fun hasNext() = index < childCount override fun next() = getChildAt(index++) ?: throw IndexOutOfBoundsException() override fun remove() = removeViewAt(--index) }
71. operator fun ViewGroup.iterator() = object : MutableIterator<View> { private var index = 0 override fun hasNext() = index < childCount override fun next() = getChildAt(index++) ?: throw IndexOutOfBoundsException() override fun remove() = removeViewAt(--index) } for (view in userLayout) { // Do something with view… }
72. operator fun ViewGroup.iterator() = object : MutableIterator<View> { private var index = 0 override fun hasNext() = index < childCount override fun next() = getChildAt(index++) ?: throw IndexOutOfBoundsException() override fun remove() = removeViewAt(--index) } for (view in userLayout) { // Do something with view… }
73. operator fun ViewGroup.iterator() = object : MutableIterator<View> { private var index = 0 override fun hasNext() = index < childCount override fun next() = getChildAt(index++) ?: throw IndexOutOfBoundsException() override fun remove() = removeViewAt(--index) } for (view in userLayout) { // Do something with view… }
74. KTX Principles Adapt existing functionality and redirect features upstream
75. KTX Principles Adapt existing functionality and redirect features upstream Default to inline unless code size or allocation is prohibitive
76. inline fun ViewGroup.forEachIndexed(action: (Int, View) -> Unit) { for (index in 0 until childCount) { action(index, getChildAt(index)) }Z }Z val userLayout: ViewGroup = findViewById(R.id.users) userLayout.forEachIndexed { index, view -> // Do something with index and view… }A
77. inline fun <reified T> Context.systemService() = ContextCompat.getSystemService(this, T::class.java) // In an Activity… val notifications = systemService<NotificationManager>()H
78. inline fun View.updatePadding( left: Int = paddingLeft, top: Int = paddingTop, right: Int = paddingRight, bottom: Int = paddingBottom ) { setPadding(left, top, right, bottom) }A avatarView.updatePadding(left = 10, right = 10)R
79. inline operator fun Rect.component1() = left inline operator fun Rect.component2() = top inline operator fun Rect.component3() = right inline operator fun Rect.component4() = bottom val (left,T_,Rright) = avatarView.clipBounds // Use left, right…
80. inline fun CharSequence.isDigitsOnly() = TextUtils.isDigitsOnly(this)Z val onlyDigits = phoneNumber.isDigitsOnly()L
81. operator fun ViewGroup.iterator() = object : MutableIterator<View> { private var index = 0 override fun hasNext() = index < childCount override fun next() = getChildAt(index++) ?: throw IndexOutOfBoundsException() override fun remove() = removeViewAt(--index) } for (view in userLayout) { // Do something with view… }
82. KTX Principles Adapt existing functionality and redirect features upstream Default to inline unless code size or allocation is prohibitive
83. KTX Principles Adapt existing functionality and redirect features upstream Default to inline unless code size or allocation is prohibitive Leverage features unique to Kotlin
84. view.setOnClickListener { // React to click… }Z
85. fun View.click(listener: (View) -> Unit) { setOnClickListener(listener) }Y view.setOnClickListener {P // React to click… }Z
86. fun View.click(listener: (View) -> Unit) { setOnClickListener(listener) }Y view.setOnClickListener {P // React to click… }Z c
87. fun View.click(listener: (View) -> Unit) { setOnClickListener(listener) }Y view.click {P // React to click… }Z C
88. view.click {P // React to click… }Z view.setOnClickListener { // React to click… }
89. KTX Principles Adapt existing functionality and redirect features upstream Default to inline unless code size or allocation is prohibitive Leverage features unique to Kotlin
90. KTX Principles Adapt existing functionality and redirect features upstream Default to inline unless code size or allocation is prohibitive Leverage features unique to Kotlin Code golf APIs to be as short as possible
91. if (Build.VERSION.SDK_INT >= 19) { TransitionManager.beginDelayedTransition(viewGroup) }Z
92. inline fun onApi(level: Int, body: () -> Unit) { if (Build.VERSION.SDK_INT >= level) { body() }Z } if (Build.VERSION.SDK_INT > 19) { TransitionManager.beginDelayedTransition(viewGroup) }Z
93. inline fun onApi(level: Int, body: () -> Unit) { if (Build.VERSION.SDK_INT >= level) { body() }Z }Q if (Build.VERSION.SDK_INT > 19) { TransitionManager.beginDelayedTransition(viewGroup) }Z onApi
94. inline fun onApi(level: Int, body: () -> Unit) { if (Build.VERSION.SDK_INT >= level) { body() }Z }Q onApi(19) { TransitionManager.beginDelayedTransition(viewGroup) }Z
95. onApi(19) { TransitionManager.beginDelayedTransition(viewGroup) }Z
96. onApi(19) { TransitionManager.beginDelayedTransition(viewGroup) }Z if (Build.VERSION.SDK_INT >= 19) { TransitionManager.beginDelayedTransition(viewGroup) }Z
97. if (SDK_INT >= 19) { TransitionManager.beginDelayedTransition(viewGroup) }Z onApi(19) { TransitionManager.beginDelayedTransition(viewGroup) }Z
98. if (SDK_INT >= 19) { TransitionManager.beginDelayedTransition(viewGroup) }Z onApi(19) { TransitionManager.beginDelayedTransition(viewGroup) }Z
99. if (SDK_INT >= 19) { TransitionManager.beginDelayedTransition(viewGroup) }Zelse { // Something… } onApi(19) { TransitionManager.beginDelayedTransition(viewGroup) }Z
100. if (SDK_INT >= 19) { TransitionManager.beginDelayedTransition(viewGroup) }Zelse { // Something… }L onApi(19)F{A TransitionManager.beginDelayedTransition(viewGroup) },
101. if (SDK_INT >= 19) { TransitionManager.beginDelayedTransition(viewGroup) }Zelse { // Something… }L onApi(19, {A TransitionManager.beginDelayedTransition(viewGroup) }, {T // Something… })F
102. if (SDK_INT >= 28) { // Fancy new thing… } else if (SDK_INT >= 19) { TransitionManager.beginDelayedTransition(viewGroup) }Zelse { // Something… }L onApi(19, {A TransitionManager.beginDelayedTransition(viewGroup) },Z{T // Something… })F
103. if (SDK_INT >= 28) { // Fancy new thing… } else if (SDK_INT >= 19) { TransitionManager.beginDelayedTransition(viewGroup) }Zelse { // Something… }L onApi(19, {A TransitionManager.beginDelayedTransition(viewGroup) },Z{T // Something… })F
104. KTX Principles Adapt existing functionality and redirect features upstream Default to inline unless code size or allocation is prohibitive Leverage features unique to Kotlin Code golf APIs to be as short as possible
105. KTX Principles Adapt existing functionality and redirect features upstream Default to inline unless code size or allocation is prohibitive Leverage features unique to Kotlin Code golf APIs to be as short as possible Optimize for a single and/or specific use case
106. Android KTX Android framework core core-ktx fragment-ktx fragment palette-ktx palette collection-ktx collection lifecycle-reactivestreams-ktx lifecycle-reactivestreams sqlite-ktx sqlite navigation-*-ktx navigation-* work-runtime-ktx work-runtime
107. Android KTX Android framework core core-ktx fragment-ktx fragment palette-ktx palette collection-ktx collection lifecycle-reactivestreams-ktx lifecycle-reactivestreams sqlite-ktx sqlite navigation-*-ktx navigation-* work-runtime-ktx work-runtime
108. supportFragmentManager.beginTransaction() .replace(android.R.id.content, userFragment) .commit()
109. inline fun FragmentManager.transaction( body: FragmentTransaction.() -> Unit ) { val transaction = beginTransaction() transaction.body() transaction.commit() } supportFragmentManager.beginTransaction() .replace(android.R.id.content, userFragment) .commit()
110. inline fun FragmentManager.transaction( body: FragmentTransaction.() -> Unit ) { val transaction = beginTransaction() transaction.body() transaction.commit() }A supportFragmentManager.beginTransaction() .replace(android.R.id.content, userFragment) t .commit()
111. inline fun FragmentManager.transaction( body: FragmentTransaction.() -> Unit ) { val transaction = beginTransaction() transaction.body() transaction.commit() }A supportFragmentManager.transaction { replace(android.R.id.content, userFragment) }Z T
112. inline fun FragmentManager.transaction( allowStateLoss: Boolean = false body: FragmentTransaction.() -> Unit ) { val transaction = beginTransaction() transaction.body() if (allowStateLoss) transaction.commitAllowingStateLoss() else transaction.commit() }A supportFragmentManager.transaction { replace(android.R.id.content, userFragment) }Z
113. inline fun FragmentManager.transaction( allowStateLoss: Boolean = false body: FragmentTransaction.() -> Unit ) { val transaction = beginTransaction() transaction.body() if (allowStateLoss) transaction.commitAllowingStateLoss() else transaction.commit() }A supportFragmentManager.transaction {G replace(android.R.id.content, userFragment) }Z
114. inline fun FragmentManager.transaction( allowStateLoss: Boolean = false, body: FragmentTransaction.() -> Unit ) { val transaction = beginTransaction() transaction.body() if (allowStateLoss) transaction.commitAllowingStateLoss() else transaction.commit() }A supportFragmentManager.transaction(allowStateLoss = true) {G replace(android.R.id.content, userFragment) }Z
115. L7 ALOAD 3 INVOKEVIRTUAL androidx/fragment/app/FragmentManager beginTransaction() Landroidx/fragment/app/FragmentTransaction; ASTORE 7 L8 ALOAD 7 LDC 16908290 ALOAD 2 INVOKEVIRTUAL androidx/fragment/app/FragmentTransaction replace( I Landroidx/fragment/app/Fragment; ) Landroidx/fragment/app/FragmentTransaction; POP L9 ALOAD 7 INVOKEVIRTUAL androidx/fragment/app/FragmentTransaction commitAllowingStateLoss() I POP
116. inline fun FragmentManager.transaction( allowStateLoss: Boolean = false, body: FragmentTransaction.() -> Unit ) { val transaction = beginTransaction() transaction.body() if (allowStateLoss) transaction.commitAllowingStateLoss() else transaction.commit() }A supportFragmentManager.transaction(allowStateLoss = true) {G replace(android.R.id.content, userFragment) }Z
117. inline fun FragmentManager.transaction( now: Boolean = false, allowStateLoss: Boolean = false, body: FragmentTransaction.() -> Unit ) { val transaction = beginTransaction() transaction.body() if (now) { if (allowStateLoss) transaction.commitNowAllowingStateLoss() else transaction.commitNow() } else { if (allowStateLoss) transaction.commitAllowingStateLoss() else transaction.commit() } }A
122. Building Kotlin-friendly libraries
123. Building Kotlin-friendly libraries • Port public API or entire library to Kotlin
124. Building Kotlin-friendly libraries • Port public API or entire library to Kotlin • Ship sibling artifact with Kotlin extensions
125. Building Kotlin-friendly libraries • Port public API or entire library to Kotlin • Ship sibling artifact with Kotlin extensions • ???
126. inline fun CharSequence.isDigitsOnly() = TextUtils.isDigitsOnly(this) val onlyDigits = phoneNumber.isDigitsOnly()
127. class TextUtils { static boolean isDigitsOnly(CharSequence str) { int len = str.length(); // … }Y }Z inline fun CharSequence.isDigitsOnly() = TextUtils.isDigitsOnly(this) val onlyDigits = phoneNumber.isDigitsOnly()
128. class TextUtils { static boolean isDigitsOnly(@NonNull CharSequence str) { int len = str.length(); // … }Y }Z inline fun CharSequence.isDigitsOnly() = TextUtils.isDigitsOnly(this) val onlyDigits = phoneNumber.isDigitsOnly()
129. class TextUtils { static boolean isDigitsOnly(@NonNull CharSequence str) { int len = str.length(); // … }Y }Z inline fun CharSequence.isDigitsOnly() = TextUtils.isDigitsOnly(this) val onlyDigits = phoneNumber.isDigitsOnly()
130. class TextUtils { @ExtensionFunction static boolean isDigitsOnly(@NonNull CharSequence str) { int len = str.length(); // … }Y }Z inline fun CharSequence.isDigitsOnly() = TextUtils.isDigitsOnly(this) val onlyDigits = phoneNumber.isDigitsOnly()
131. class TextUtils { @ExtensionFunction static boolean isDigitsOnly(@NonNull CharSequence str) { int len = str.length(); // … }Y }Z inline fun CharSequence.isDigitsOnly() = TextUtils.isDigitsOnly(this) val onlyDigits = phoneNumber.isDigitsOnly()
132. class TextUtils { @ExtensionFunction static boolean isDigitsOnly(@NonNull CharSequence str) { int len = str.length(); // … }Y }Z val onlyDigits = phoneNumber.isDigitsOnly()
133. class TextUtils { @ExtensionFunction static boolean isDigitsOnly(@NonNull CharSequence str) { int len = str.length(); // … }Y }Z val onlyDigits = phoneNumber.isDigitsOnly()
134. class TextUtils { @ExtensionFunction static boolean isDigitsOnly(@NonNull CharSequence str) { int len = str.length(); // … }Y }Z val onlyDigits = phoneNumber.isDigitsOnly() // in the bytecode we get val onlyDigits = TextUtils.isDigitsOnly(phoneNumber)
135. inline fun View.updatePadding( left: Int = paddingLeft, top: Int = paddingTop, right: Int = paddingRight, bottom: Int = paddingBottom ) { setPadding(left, top, right, bottom) }A avatarView.updatePadding(left = 10, right = 10)R
136. inline fun View.updatePadding( left: Int = paddingLeft, top: Int = paddingTop, right: Int = paddingRight, bottom: Int = paddingBottom ) { setPadding(left, top, right, bottom) }A avatarView.updatePadding(left = 10, right = 10)R
137. class View { void setPadding(int left, int top, int right, int bottom) { /* … */ }B }A inline fun View.updatePadding( left: Int = paddingLeft, top: Int = paddingTop, right: Int = paddingRight, bottom: Int = paddingBottom ) { setPadding(left, top, right, bottom) }A avatarView.updatePadding(left = 10, right = 10)R
138. class View { void setPadding( @KtName("left")Aint left, @KtName("top")Aint top, @KtName("right")Aint right, @KtName("bottom")Aint bottom ) { /* … */ }B }A inline fun View.updatePadding( left: Int = paddingLeft, top: Int = paddingTop, right: Int = paddingRight, bottom: Int = paddingBottom ) { setPadding(left, top, right, bottom)
139. class View { void setPadding( @KtName("left")A@DefaultValue("paddingLeft") int left, @KtName("top")A@DefaultValue("paddingTop") int top, @KtName("right")A@DefaultValue("paddingRight") int right, @KtName("bottom")A@DefaultValue("paddingBottom") int bottom ) { /* … */ }B }A inline fun View.updatePadding( left: Int = paddingLeft, top: Int = paddingTop, right: Int = paddingRight, bottom: Int = paddingBottom ) { setPadding(left, top, right, bottom)
140. class View { void setPadding( @KtName("left") @DefaultValue("paddingLeft") int left, @KtName("top") @DefaultValue("paddingTop") int top, @KtName("right") @DefaultValue("paddingRight") int right, @KtName("bottom") @DefaultValue("paddingBottom") int bottom ) { /* … */ }B }A avatarView.updatePadding(left = 10, right = 10)R
141. class View { void setPadding( @KtName("left") @DefaultValue("paddingLeft") int left, @KtName("top") @DefaultValue("paddingTop") int top, @KtName("right") @DefaultValue("paddingRight") int right, @KtName("bottom") @DefaultValue("paddingBottom") int bottom ) { /* … */ }B }A avatarView.setPadding(left = 10, right = 10)R u p d a t e
142. class View { void setPadding( @KtName("left") @DefaultValue("paddingLeft") int left, @KtName("top") @DefaultValue("paddingTop") int top, @KtName("right") @DefaultValue("paddingRight") int right, @KtName("bottom") @DefaultValue("paddingBottom") int bottom ) { /* … */ }B }A avatarView.setPadding(left = 10, right = 10)R // in bytecode we get avatarView.setPadding( 10, avatarView.paddingTop, 10, avatarView.paddingBottom) u p d a t e
143. KEEP-110
144. KEEP-110 • @ExtensionFunction / @ExtensionProperty — Turn a static method with at least one argument into an extension function or an extension property.
145. KEEP-110 • @ExtensionFunction / @ExtensionProperty — Turn a static method with at least one argument into an extension function or an extension property. • 
 
 • @DefaultValue — Default parameter values.
146. KEEP-110 • @ExtensionFunction / @ExtensionProperty — Turn a static method with at least one argument into an extension function or an extension property. • 
 
 • @DefaultValue — Default parameter values. • 
 
 • @KtName — An alternate name for methods, fields, and parameters for use by Kotlin code.
147. Building Kotlin-friendly libraries • Port public API or entire library to Kotlin • Ship sibling artifact with Kotlin extensions • ???
148. Building Kotlin-friendly libraries • Port public API or entire library to Kotlin • Ship sibling artifact with Kotlin extensions • KEEP-110 annotations
149. Android KTX Android framework core core-ktx fragment-ktx fragment palette-ktx palette collection-ktx collection lifecycle-reactivestreams-ktx lifecycle-reactivestreams sqlite-ktx sqlite navigation-*-ktx navigation-* work-runtime-ktx work-runtime
154. https://github.com/Kotlin/KEEP/issues/110
155. Jake Wharton Thank you @JakeWharton