Android KTXAndroid KTX Jake Wharton. Android KTX Jake Wharton. val userLayout: ViewGroup =...

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Transcript of Android KTXAndroid KTX Jake Wharton. Android KTX Jake Wharton. val userLayout: ViewGroup =...

Android KTX

Jake Wharton

Android KTX

Jake Wharton

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… }

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

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

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

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)

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

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

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

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

// In an Activity, on API 23+… val notifications = getSystemService(NotificationManager::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)

// 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)

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)

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)

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

inline fun <reified T> Context.systemService() = ContextCompat.getSystemService(this, T::class.java)

// In an Activity… val notifications = systemService<NotificationManager>()H S

inline fun <reified T> Context.systemService() = ContextCompat.getSystemService(this, T::class.java)

// In an Activity… val notifications = systemService<NotificationManager>()H

avatarView.setPadding( 10, avatarView.paddingTop, 10, avatarView.paddingBottom)

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)

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)

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

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

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

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

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

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…

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

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…

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…

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…

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…

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…

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…

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…

var onlyDigits = true for (c in phoneNumber) {A if (!c.isDigit()) { onlyDigits = false break }G }B

r true for (c in ) if (!c. ) { onlyDigits = false break }G

val onlyDigits = phoneNumber.all {Ait.isDigit() }B

.all {Ait.isDigit() }Bval onlyDigits = TextUtils.isDigitsOnly(phoneNumber)

inline fun CharSequence.isDigitsOnly() = TextUtils.isDigitsOnly(this)Z

val onlyDigits = TextUtils.isDigitsOnly(phoneNumber)L

inline fun CharSequence.isDigitsOnly() = TextUtils.isDigitsOnly(this)Z

val onlyDigits = phoneNumber.isDigitsOnly()L

inline fun CharSequence.isDigitsOnly() = TextUtils.isDigitsOnly(this)Z

val onlyDigits = phoneNumber.

inline fun CharSequence.isDigitsOnly() = TextUtils.isDigitsOnly(this)Z

val onlyDigits = phoneNumber.

inline fun CharSequence.isDigitsOnly() = TextUtils.isDigitsOnly(this)Z

val onlyDigits = phoneNumber.is

inline fun CharSequence.isDigitsOnly() = TextUtils.isDigitsOnly(this)Z

val onlyDigits = phoneNumber.is

inline fun CharSequence.isDigitsOnly() = TextUtils.isDigitsOnly(this)Z

val onlyDigits = phoneNumber.isDigitsOnly()L

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

core-ktx

Android KTX

Android KTXcore-ktx Android framework

Android KTXAndroid frameworksupport-compatcore-ktx

Android KTXAndroid frameworkcorecore-ktx

Android KTXAndroid frameworkcorecore-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

Android KTXAndroid frameworkcorecore-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

@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) }

@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) }

@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) }

public final class ColorUtils { }Z

public final class ColorUtils { @ColorInt public static int compositeColors( @ColorInt int foreground, @ColorInt int background) { // … }X }Z

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

@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) }

@RequiresApi(26) inline operator fun Color.plus(c: Color): Color = ColorUtils.compositeColors(c, this)

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

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

KTX Principles

KTX Principles

Adapt existing functionality and redirect features upstream

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

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

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

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) }

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… }

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… }

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… }

KTX Principles

Adapt existing functionality and redirect features upstream

KTX Principles

Adapt existing functionality and redirect features upstream

Default to inline unless code size or allocation is prohibitive

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

inline fun <reified T> Context.systemService() = ContextCompat.getSystemService(this, T::class.java)

// In an Activity… val notifications = systemService<NotificationManager>()H

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

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…

inline fun CharSequence.isDigitsOnly() = TextUtils.isDigitsOnly(this)Z

val onlyDigits = phoneNumber.isDigitsOnly()L

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… }

KTX Principles

Adapt existing functionality and redirect features upstream

Default to inline unless code size or allocation is prohibitive

KTX Principles

Adapt existing functionality and redirect features upstream

Default to inline unless code size or allocation is prohibitive

Leverage features unique to Kotlin

view.setOnClickListener { // React to click… }Z

fun View.click(listener: (View) -> Unit) { setOnClickListener(listener) }Y

view.setOnClickListener {P // React to click… }Z

fun View.click(listener: (View) -> Unit) { setOnClickListener(listener) }Y

view.setOnClickListener {P // React to click… }Z

c

fun View.click(listener: (View) -> Unit) { setOnClickListener(listener) }Y

view.click {P // React to click… }Z

C

view.click {P // React to click… }Z

view.setOnClickListener { // React to click… }

KTX Principles

Adapt existing functionality and redirect features upstream

Default to inline unless code size or allocation is prohibitive

Leverage features unique to Kotlin

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

if (Build.VERSION.SDK_INT >= 19) { TransitionManager.beginDelayedTransition(viewGroup) }Z

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

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

inline fun onApi(level: Int, body: () -> Unit) { if (Build.VERSION.SDK_INT >= level) { body() }Z }Q

onApi(19) { TransitionManager.beginDelayedTransition(viewGroup) }Z

onApi(19) { TransitionManager.beginDelayedTransition(viewGroup) }Z

onApi(19) { TransitionManager.beginDelayedTransition(viewGroup) }Z

if (Build.VERSION.SDK_INT >= 19) { TransitionManager.beginDelayedTransition(viewGroup) }Z

if (SDK_INT >= 19) { TransitionManager.beginDelayedTransition(viewGroup) }Z

onApi(19) { TransitionManager.beginDelayedTransition(viewGroup) }Z

if (SDK_INT >= 19) { TransitionManager.beginDelayedTransition(viewGroup) }Z

onApi(19) { TransitionManager.beginDelayedTransition(viewGroup) }Z

if (SDK_INT >= 19) { TransitionManager.beginDelayedTransition(viewGroup) }Zelse { // Something… }

onApi(19) { TransitionManager.beginDelayedTransition(viewGroup) }Z

if (SDK_INT >= 19) { TransitionManager.beginDelayedTransition(viewGroup) }Zelse { // Something… }L

onApi(19)F{A TransitionManager.beginDelayedTransition(viewGroup) },

if (SDK_INT >= 19) { TransitionManager.beginDelayedTransition(viewGroup) }Zelse { // Something… }L

onApi(19, {A TransitionManager.beginDelayedTransition(viewGroup) }, {T // Something… })F

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

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

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

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

Android KTXAndroid frameworkcorecore-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

Android KTXAndroid frameworkcorecore-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

supportFragmentManager.beginTransaction() .replace(android.R.id.content, userFragment) .commit()

inline fun FragmentManager.transaction( body: FragmentTransaction.() -> Unit ) { val transaction = beginTransaction() transaction.body() transaction.commit() }

supportFragmentManager.beginTransaction() .replace(android.R.id.content, userFragment) .commit()

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()

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

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

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

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

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

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

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

Building Kotlin-friendly libraries

Building Kotlin-friendly libraries

• Port public API or entire library to Kotlin

Building Kotlin-friendly libraries

• Port public API or entire library to Kotlin

• Ship sibling artifact with Kotlin extensions

Building Kotlin-friendly libraries

• Port public API or entire library to Kotlin

• Ship sibling artifact with Kotlin extensions

• ???

inline fun CharSequence.isDigitsOnly() = TextUtils.isDigitsOnly(this)

val onlyDigits = phoneNumber.isDigitsOnly()

class TextUtils { static boolean isDigitsOnly(CharSequence str) { int len = str.length(); // … }Y }Z

inline fun CharSequence.isDigitsOnly() = TextUtils.isDigitsOnly(this)

val onlyDigits = phoneNumber.isDigitsOnly()

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()

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()

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()

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()

class TextUtils { @ExtensionFunction static boolean isDigitsOnly(@NonNull CharSequence str) { int len = str.length(); // … }Y }Z

val onlyDigits = phoneNumber.isDigitsOnly()

class TextUtils { @ExtensionFunction static boolean isDigitsOnly(@NonNull CharSequence str) { int len = str.length(); // … }Y }Z

val onlyDigits = phoneNumber.isDigitsOnly()

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)

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

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

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

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) }A

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) }A

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

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 update

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)

update

KEEP-110

KEEP-110

• @ExtensionFunction / @ExtensionProperty — Turn a static

method with at least one argument into an extension function or an

extension property.

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.

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.

Building Kotlin-friendly libraries

• Port public API or entire library to Kotlin

• Ship sibling artifact with Kotlin extensions

• ???

Building Kotlin-friendly libraries

• Port public API or entire library to Kotlin

• Ship sibling artifact with Kotlin extensions

• KEEP-110 annotations

Android KTXAndroid frameworkcorecore-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

https://github.com/Kotlin/KEEP/issues/110

Jake Wharton

Thank you

@JakeWharton

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