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Android KTX
A dash of Kotlin makes
all the difference!
@dankim
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Android KTX
A dash of Kotlin makes
all the difference!
@dankim
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What is KTX?
(besides just a cool name)
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Kotlin extensions designed
specifically for Android
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So why should I care?
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Makes Android development more
concise, pleasant, and idiomatic®
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Writing clean, readable code is a
lot easier and a lot more fun
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Android has a long,
colorful history
Android has a long,
colorful history
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view.addOnLayoutChangeListener(object : View.OnLayoutChangeListener {
override fun onLayoutChange(
view: View?,
left: Int,
top: Int,
right: Int,
bottom: Int,
oldLeft: Int,
oldTop: Int,
oldRight: Int,
oldBottom: Int
) {
doSomething()
}
})
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view.addOnLayoutChangeListener(object : View.OnLayoutChangeListener {
override fun onLayoutChange(
view: View?,
left: Int,
top: Int,
right: Int,
bottom: Int,
oldLeft: Int,
oldTop: Int,
oldRight: Int,
oldBottom: Int
) {
doSomething()
}
})
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// Original
view.addOnLayoutChangeListener(object : View.OnLayoutChangeListener {
override fun onLayoutChange(
view: View?,
left: Int,
top: Int,
right: Int,
bottom: Int,
oldLeft: Int,
oldTop: Int,
oldRight: Int,
oldBottom: Int
) {
...
}
})
// KTX
view.doOnNextLayout { doSomething() }
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You can learn a lot
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Are we adding any
new functionality?
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Are we leveraging
Kotlin-specific language features?
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Will the extension be useful
in the long-term?
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Does the extension provide a
meaningful upgrade?
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Is the intent
of the extension clear?
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Enough talk, more code!
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repositories {
google()
}
dependencies {
implementation 'androidx.core:core-ktx:1.0.0'
}
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androidx.core:core-ktx
androidx.fragment:fragment-ktx
androidx.palette:palette-ktx
androidx.sqlite:sqlite-ktx
androidx.collection:collection-ktx
androidx.lifecycle:lifecycle-viewmodel-ktx
androidx.lifecycle:lifecycle-reactivestreams-ktx
android.arch.navigation:navigation-common-ktx
android.arch.navigation:navigation-fragment-ktx
android.arch.navigation:navigation-runtime-ktx
android.arch.navigation:navigation-testing-ktx
android.arch.navigation:navigation-ui-ktx
android.arch.work:work-runtime-ktx
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androidx.core:core-ktx
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androidx.core.animation
androidx.core.content
androidx.core.graphics
androidx.core.graphics.drawable
androidx.core.net
androidx.core.os
androidx.core.preference
androidx.core.text
androidx.core.transition
androidx.core.util
androidx.core.view
androidx.core.widget
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A note about examples
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Named parameters &
default values
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drawable.setBounds(drawable.bounds.left,
drawable.bounds.top,
drawable.bounds.right,
100)
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// Original
drawable.setBounds(drawable.bounds.left,
drawable.bounds.top,
drawable.bounds.right,
100)
// KTX
drawable.updateBounds(bottom = 100)
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// Implementation
fun Drawable.updateBounds(@Px left: Int = bounds.left,
@Px top: Int = bounds.top,
@Px right: Int = bounds.right,
@Px bottom: Int = bounds.bottom) {xx
setBounds(left, top, right, bottom)
}xx
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// Original
animator.addListener(object : Animator.AnimatorListener {
override fun onAnimationEnd(a: Animator?) { ... }
override fun onAnimationStart(a: Animator?) { }
override fun onAnimationCancel(a: Animator?) { }
override fun onAnimationRepeat(a: Animator?) { }
})x
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// Original
animator.addListener(object : Animator.AnimatorListener {
override fun onAnimationEnd(a: Animator?) { ... }
override fun onAnimationStart(a: Animator?) { }
override fun onAnimationCancel(a: Animator?) { }
override fun onAnimationRepeat(a: Animator?) { }
})x
// KTX
animator.addListener(onEnd = { ... })
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// Original
animator.addListener(object : Animator.AnimatorListener {
override fun onAnimationEnd(a: Animator?) { ... }
override fun onAnimationStart(a: Animator?) { }
override fun onAnimationCancel(a: Animator?) { }
override fun onAnimationRepeat(a: Animator?) { }
})
// KTX
animator.addListener(onEnd = { ... })
animator.doOnEnd { ... }
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// Implementation
fun Animator.doOnEnd(crossinline action: (a: Animator) -> Unit) =
addListener(onEnd = action)
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// Implementation
fun Animator.doOnEnd(crossinline action: (a: Animator) -> Unit) =
addListener(onEnd = action)
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// Implementation
inline fun Animator.addListener(
crossinline onEnd: (a: Animator) -> Unit = {},
crossinline onStart: (a: Animator) -> Unit = {},
crossinline onCancel: (a: Animator) -> Unit = {},
crossinline onRepeat: (a: Animator) -> Unit = {}
): Animator.AnimatorListener {x
...
}x
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animator.doOnEnd { }
animator.doOnCancel { }
animator.doOnPause { }
animator.doOnRepeat { }
animator.doOnResume { }
animator.doOnStart { }
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transition.addListener(object : Transition.TransitionListener {
override fun onTransitionEnd(t: Transition?) { ... }
override fun onTransitionStart(t: Transition?) { }
override fun onTransitionCancel(t: Transition) { }
override fun onTransitionResume(t: Transition?) { }
override fun onTransitionPause(t: Transition?) { }
})x
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// Original
transition.addListener(object : Transition.TransitionListener {
override fun onTransitionEnd(t: Transition?) { ... }
override fun onTransitionStart(t: Transition?) { }
override fun onTransitionCancel(t: Transition) { }
override fun onTransitionResume(t: Transition?) { }
override fun onTransitionPause(t: Transition?) { }
})x
// KTX
transition.addListener(onEnd = { ... })
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// Original
transition.addListener(object : Transition.TransitionListener {
override fun onTransitionEnd(t: Transition?) { ... }
override fun onTransitionStart(t: Transition?) { }
override fun onTransitionCancel(t: Transition) { }
override fun onTransitionResume(t: Transition?) { }
override fun onTransitionPause(t: Transition?) { }
})
// KTX
transition.addListener(onEnd = { ... })
transition.doOnEnd { ... }
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Operator Overloading
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a++
a--
a + b
a += b
a * b
a / b
a % b
a..b
a in b
a[i]
a[i] = b
...
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bitmap.getPixel(100, 100)
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// Original
bitmap.getPixel(100, 100)
// KTX
bitmap[100, 100]
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// Implementation
inline operator fun Bitmap.get(x: Int, y: Int) = getPixel(x, y)
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// Implementation
inline operator fun Bitmap.get(x: Int, y: Int) = ...
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bitmap.setPixel(100, 100, colorInt)
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// Original
bitmap.setPixel(100, 100, colorInt)
// KTX
bitmap[100, 100] = colorInt
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// Implementation
inline operator fun Bitmap.set(
x: Int,
y: Int,
@ColorInt color: Int) = setPixel(x, y, color)
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// Implementation
inline operator fun Bitmap.set(
x: Int,
y: Int,
@ColorInt color: Int) = setPixel(x, y, color)
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rect.union(rect2)
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// Original
rect.union(rect2)
// KTX
rect + rect2
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// Implementation
inline operator fun Rect.plus(r: Rect): Rect {
return Rect(this).apply {
union(r)
}xx
}xx
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// Implementation
inline operator fun Rect.plus(r: Rect): Rect {
return Rect(this).apply {
union(r)
}x
}x
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menu.removeItem(menuItem.itemId)
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// Original
menu.removeItem(menuItem.itemId)
// KTX
menu -= menuItem
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// Implementation
inline operator fun Menu.minusAssign(item: MenuItem) =
removeItem(item.itemId)
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// Implementation
inline
operator fun Menu.
minusAssign(item: MenuItem) =
removeItem(item.itemId)
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Destructuring
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val lat = location.latitude
val long = location.longitude
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// Original
val lat = location.latitude
val long = location.longitude
// KTX
val (lat, long) = location
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// Implementation
inline operator fun Location.component1() = this.latitude
inline operator fun Location.component2() = this.longitude
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// Implementation
inline operator fun Location.component1() = this.latitude
inline operator fun Location.component2() = this.longitude
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val left = rect.left
val top = rect.top
val right = rect.right
val bottom = rect.bottom
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// Original
val left = rect.left
val top = rect.top
val right = rect.right
val bottom = rect.bottom
// KTX
val (left, top, right, bottom) = rect
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inline operator fun Rect.component1() = this.left
inline operator fun Rect.component2() = this.top
inline operator fun Rect.component3() = this.right
inline operator fun Rect.component4() = this.bottom
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inline operator fun Rect.component1() = this.left
inline operator fun Rect.component2() = this.top
inline operator fun Rect.component3() = this.right
inline operator fun Rect.component4() = this.bottom
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val red = colorInt.red
val green = colorInt.green
val blue = colorInt.blue
val alpha = colorInt.alpha
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// Original
val red = colorInt.red
val green = colorInt.green
val blue = colorInt.blue
val alpha = colorInt.alpha
// KTX
val (red, green, blue, alpha) = colorInt
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// Implementation
fun @receiver:ColorInt Int.component1() = (this shr 24) and 0xff
fun @receiver:ColorInt Int.component2() = (this shr 16) and 0xff
fun @receiver:ColorInt Int.component3() = (this shr 8) and 0xff
fun @receiver:ColorInt Int.component4() = this and 0xffx
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// Implementation
fun @receiver:ColorInt Int.component1() = (this shr 24) and 0xff
fun @receiver:ColorInt Int.component2() = (this shr 16) and 0xff
fun @receiver:ColorInt Int.component3() = (this shr 8) and 0xff
fun @receiver:ColorInt Int.component4() = this and 0xffx
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Pseudo Collections
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viewGroup.childCount != 0
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// Original
viewGroup.childCount != 0
// KTX
viewGroup.isEmpty()
viewGroup.isNotEmpty()
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// Implementation
inline fun ViewGroup.isEmpty() = childCount == 0
inline fun ViewGroup.isNotEmpty() = childCount != 0
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for (index in 0 until viewGroup.childCount) {
doSomething(viewGroup.getChildAt(index))
}
x
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// Original
for (index in 0 until viewGroup.childCount) {
doSomething(viewGroup.getChildAt(index))
}
x
// KTX
viewGroup.forEach { doSomething() }
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// Implementation
inline fun ViewGroup.forEach(action: (view: View) -> Unit) {
for (index in 0 until childCount) {
action(getChildAt(index))
}
x
}
x
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// Implementation
inline fun ViewGroup.forEach(action: (view: View) -> Unit) {
for (index in 0 until childCount) {
action(getChildAt(index))
}
x
}
x
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viewGroup.indexOfChild(view) != -1
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// Original
viewGroup.indexOfChild(view) != -1
// KTX
viewGroup.contains(view)
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// Implementation
inline operator fun ViewGroup.contains(view: View) =
indexOfChild(view) != -1
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// Implementation
inline operator fun ViewGroup.contains(view: View) =
indexOfChild(view) != -1
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viewGroup.contains(view.textView)
viewGroup.forEach { ... }
viewGroup.forEachIndexed { index, view -> ... }
viewGroup.size
viewGroup.isEmpty()
viewGroup.isNotEmpty()
val view = viewGroup[0]
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for (index in 0 until menu.size()) {
if (menu.getItem(index) == menuItem) {
return true
}
x
}
x
return false
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// Original
for (index in 0 until menu.size()) {
if (menu.getItem(index) == menuItem) {
return true
}
x
}
x
return false
// KTX
menu.contains(menuItem)
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// Implementation
operator fun Menu.contains(item: MenuItem): Boolean {
for (index in 0 until size()) {
if (getItem(index) == item) {
return true
}
x
}
x
return false
}
x
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// Implementation
operator fun Menu.contains(item: MenuItem): Boolean {
for (index in 0 until size()) {
if (getItem(index) == item) {
return true
}
x
}
x
return false
}
x
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menu.contains(menuItem)
menu.size
menu.isEmpty()
menu.isNotEmpty()
menu.forEach { ... }
menu.forEachIndexed { i, item -> ... }
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Making Life Easier /
Discoverability
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Bitmap.createBitmap(100,
100,
Bitmap.Config.ARGB_8888,
true,
ColorSpace.get(ColorSpace.Named.SRGB))
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// Original
Bitmap.createBitmap(100,
100,
Bitmap.Config.ARGB_8888,
true,
ColorSpace.get(ColorSpace.Named.SRGB))
// KTX
createBitmap(100, 100)
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// Implementation
inline fun createBitmap(
width: Int,
height: Int,
config: Bitmap.Config = Bitmap.Config.ARGB_8888,
hasAlpha: Boolean = true,
colorSpace: ColorSpace = ColorSpace.get(ColorSpace.Named.SRGB)
): Bitmap {
return Bitmap.createBitmap(width,
height,
config,
hasAlpha,
colorSpace)
}x
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// Implementation
inline fun createBitmap(
width: Int,
height: Int,
config: Bitmap.Config = Bitmap.Config.ARGB_8888,
hasAlpha: Boolean = true,
colorSpace: ColorSpace = ColorSpace.get(ColorSpace.Named.SRGB)
): Bitmap {
return Bitmap.createBitmap(width,
height,
config,
hasAlpha,
colorSpace)
}x
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val bitmap = Bitmap.createBitmap(100, 100, Bitmap.Config.ARGB_8888)
val canvas = Canvas(bitmap)
canvas.translate(-view.scrollX.toFloat(), -view.scrollY.toFloat())
view.draw(canvas)
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// Original
val bitmap = Bitmap.createBitmap(100, 100, Bitmap.Config.ARGB_8888)
val canvas = Canvas(bitmap)
canvas.translate(-view.scrollX.toFloat(), -view.scrollY.toFloat())
view.draw(canvas)
// KTX
view.drawToBitmap()
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sharedPrefs.edit()
.putBoolean(key, value)
.apply()
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// Original
sharedPrefs.edit()
.putBoolean( key, value
x
)
.apply()
// KTX
sharedPrefs.edit { putBoolean(key, value) }
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val builder = SpannableStringBuilder()
val start = builder.length
builder.append("Hello")
builder.setSpan(
StyleSpan(Typeface.BOLD),
start,
builder.length,
Spanned.SPAN_INCLUSIVE_EXCLUSIVE
)x
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// Original
val builder = SpannableStringBuilder()
val start = builder.length
builder.append("Hello")
builder.setSpan(
StyleSpan(Typeface.BOLD),
start,
builder.length,
Spanned.SPAN_INCLUSIVE_EXCLUSIVE
)x
// KTX
builder.bold { append("Hello") }
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// Original
val builder = SpannableStringBuilder()
val start = builder.length
builder.append("Hello")
builder.setSpan(
StyleSpan(Typeface.BOLD),
start,
builder.length,
Spanned.SPAN_INCLUSIVE_EXCLUSIVE
)x
// KTX
builder.bold { append("Hello") }
builder.bold { italic { underline { append("Hello") } } }
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bundle.putString("Hello", “KotlinConf")
bundle.putInt((“Kotlin"), 100)
bundle.putBoolean("Java", false)x
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// Original
bundle.putString("Hello", "KotlinConf")
bundle.putInt(("Kotlin"), 100)
bundle.putBoolean("Java", false)x
// KTX
bundleOf("Hello" to "KotlinConf", "Kotlin" to 100, "Java" to true)
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// Implementation
fun bundleOf(vararg pairs: Pair) = Bundle(pairs.size).apply {
for ((key, value) in pairs) {
when (value) {
null -> putString(key, null) // Any nullable type will suffice.
// Scalars
is Boolean -> putBoolean(key, value)
is Byte -> putByte(key, value)
is Char -> putChar(key, value)
is Double -> putDouble(key, value)
is Float -> putFloat(key, value)
is Int -> putInt(key, value)
is Long -> putLong(key, value)
is Short -> putShort(key, value)
// References
is Bundle -> putBundle(key, value)
is CharSequence -> putCharSequence(key, value)
is Parcelable -> putParcelable(key, value)
// Scalar arrays
is BooleanArray -> putBooleanArray(key, value)
is ByteArray -> putByteArray(key, value)
is CharArray -> putCharArray(key, value)
is DoubleArray -> putDoubleArray(key, value)
is FloatArray -> putFloatArray(key, value)
is IntArray -> putIntArray(key, value)
is LongArray -> putLongArray(key, value)
is ShortArray -> putShortArray(key, value)
// Reference arrays
is Array<*> -> {
val componentType = value::class.java.componentType
@Suppress("UNCHECKED_CAST") // Checked by reflection.
when {
Parcelable::class.java.isAssignableFrom(componentType) -> {
putParcelableArray(key, value as Array)
}
String::class.java.isAssignableFrom(componentType) -> {
putStringArray(key, value as Array)
}
CharSequence::class.java.isAssignableFrom(componentType) -> {
putCharSequenceArray(key, value as Array)
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db.beginTransaction()
try {
...x
db.setTransactionSuccessful()
} finally {
db.endTransaction()
}x
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// Original
db.beginTransaction()
try {
...x
db.setTransactionSuccessful()
} finally {
db.endTransaction()
}x
// KTX
db.transaction { ... }
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ContextCompat.getSystemService(this, AlarmManager::class.java)
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// Original
ContextCompat.getSystemService(this, AlarmManager::class.java)
// KTX
getSystemService()
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view.postDelayed({ ... }, 200)
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// Original
view.postDelayed({ ... }, 200)
// KTX
view.postDelayed(200) { ... }
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Things to keep in mind
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Conflicts with your own
extensions?
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What’s good for core-ktx is not a
value judgement on all extensions
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Should I still use Anko &
Kotlin Android Extensions?
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KEEP-110
https://github.com/Kotlin/KEEP/issues/110
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Contributing to KTX
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AOSP
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They're "just" extensions
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Low barrier to entry
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Don't be discouraged by "no"
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Start with discussion
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AOSP:
https://android.googlesource.com/platform/frameworks/support/
Issue tracker:
https://issuetracker.google.com/issues?q=componentid:
396204%20status:open
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Thank you!
@dankim