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10 Extension Functions
of Kotlin in Android
Development
@magiepooh
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About me
@magiepooh
@magie_pooh
Takuma Fujita
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Company
CyberAgent, Inc.
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10 Extension Functions
of Kotlin in Android
Development
@magiepooh
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What’s Kotlin?
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Kotlin
• By JetBrains
• Lambdas
• Nullable(NonNull)
• Higher-Order Functions (Stream)
• Extension Functions
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Kotlin
• By JetBrains
• Lambdas -> Retrolambda
• Nullable(NonNull)
• Higher-Order Functions (Stream)
• Extension Functions
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Kotlin
• By JetBrains
• Lambdas -> Retrolambda
• Nullable(NonNull) -> Optional
• Higher-Order Functions (Stream)
• Extension Functions
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Kotlin
• By JetBrains
• Lambdas -> Retrolambda
• Nullable(NonNull) -> Optional
• Higher-Order Functions (Stream) -> RxJava
• Extension Functions
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Kotlin
• By JetBrains
• Lambdas -> Retrolambda
• Nullable(NonNull) -> Optional
• Higher-Order Functions (Stream) -> RxJava
• Extension Functions
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Functions in Kotlin
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Functions in Kotlin
fun sum(a: Int, b: Int): Int {
return a + b
}
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Functions in Kotlin
fun sum(a: Int, b: Int): Int {
return a + b
}
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Functions in Kotlin
fun sum(a: Int, b: Int): Int {
return a + b
}
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Functions in Kotlin
fun sum(a: Int, b: Int): Int {
return a + b
}
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Functions in Kotlin
fun sum(a: Int, b: Int): Int = a + b
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Functions in Kotlin
fun sum(a: Int, b: Int): Int = a + b
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Functions in Kotlin
fun sum(a: Int, b: Int) = a + b
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Extension Functions
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Extension Functions
static void toast(Context context, String text) {
Toast.makeText(context, text, Toast.LENGTH_SHORT).show();
}
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Extension Functions
void toast(Context context, String text) {
Toast.makeText(context, text, Toast.LENGTH_SHORT).show();
}
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Extension Functions
fun toast(Context context, String text) {
Toast.makeText(context, text, Toast.LENGTH_SHORT).show();
}
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Extension Functions
fun toast(Context context, String text) {
Toast.makeText(context, text, Toast.LENGTH_SHORT).show();
}
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Extension Functions
fun toast(context: Context, text: String) {
Toast.makeText(context, text, Toast.LENGTH_SHORT).show()
}
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fun Activity.toast(context: Context, text: String) {
Toast.makeText(context, text, Toast.LENGTH_SHORT).show()
}
Extension Functions
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fun Activity.toast(context: Context, text: String) {
Toast.makeText(context, text, Toast.LENGTH_SHORT).show()
}
Extension Functions
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fun Activity.toast(context: Context, text: String) {
Toast.makeText(this, text, Toast.LENGTH_SHORT).show()
}
Extension Functions
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fun Activity.toast(context: Context, text: String) {
Toast.makeText(this, text, Toast.LENGTH_SHORT).show()
}
Extension Functions
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fun Activity.toast(text: String) {
Toast.makeText(this, text, Toast.LENGTH_SHORT).show()
}
Extension Functions
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fun Activity.toast(text: String) {
Toast.makeText(this, text, Toast.LENGTH_SHORT).show()
}
override fun onCreate(savedInstanceState : Bundle?) {
toast(“Hello, Toast!”)
}
Extension Functions
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fun Activity.toast(text: String) =
Toast.makeText(this, text, Toast.LENGTH_SHORT).show()
override fun onCreate(savedInstanceState : Bundle?) {
toast(“Hello, Toast!”)
}
Extension Functions
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Some Extension Functions
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toVisible
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toVisible
fun View.toVisible() {
visibility = View.VISIBLE
}
textView.toVisible()
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toVisible
fun View.toVisible() {
visibility = View.VISIBLE
}
textView.toVisible()
textView.toGone()
textView.isVisible()
textView.isGone()
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setFragment
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setFragment
fun FragmentActivity.setFragment(fragment: Fragment,
containerId: Int) =
supportFragmentManager
.beginTransaction()
.add(containerId, fragment)
.commit()
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setFragment
fun FragmentActivity.setFragment(fragment: Fragment,
containerId: Int) =
supportFragmentManager
.beginTransaction()
.add(containerId, fragment)
.commit()
setFragment(MainFragment.newInstance(),
android.R.id.content)
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setFragment
fun FragmentActivity.setFragment(fragment: Fragment,
containerId: Int) =
supportFragmentManager
.beginTransaction()
.add(containerId, fragment)
.commit()
setFragment(MainFragment.newInstance(),
android.R.id.content)
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setFragment
fun FragmentActivity.setFragment(fragment: Fragment,
containerId: Int = android.R.id.content) =
supportFragmentManager
.beginTransaction()
.add(containerId, fragment)
.commit()
setFragment(MainFragment.newInstance(),
android.R.id.content)
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setFragment
fun FragmentActivity.setFragment(fragment: Fragment,
containerId: Int = android.R.id.content) =
supportFragmentManager
.beginTransaction()
.add(containerId, fragment)
.commit()
setFragment(MainFragment.newInstance())
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setFragment
fun FragmentActivity.setFragment(fragment: Fragment,
containerId: Int = android.R.id.content) =
supportFragmentManager
.beginTransaction()
.add(containerId, fragment)
.commit()
setFragment(MainFragment.newInstance())
setFragment(MainFragment.newInstance(), R.id.my_content)
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getString
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getString(Java)
getActivity().getResources().getString(resId)
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getString
fun Fragment.getString(@StringRes resId: Int) =
getActivity().getResources().getString(resId)
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getString
fun Fragment.getString(@StringRes resId: Int) =
activity.resources.getString(resId)
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let
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let
public inline fun T.let(f: (T) -> R): R =
f(this)
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let
someObject?.let {
// `it` is non-null
}
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Compat
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isAttachedToWindow
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isAttachedToWindow
fun View.isAttachedToWindowCompat () =
if (Build.VERSION.SDK_INT < 19) {
ViewCompat.isAttachedToWindow(this)
} else {
isAttachedToWindow()
}
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Cast
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WindowManager
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WindowManager(Java)
WindowManager windowManager =
(WindowManager)
getSystemService(Context.WINDOW_SERVICE)
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WindowManager
fun Context.getWindowManager() =
getSystemService(Context.WINDOW_SERVICE)
as WindowManager
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WindowManager
fun Context.getWindowManager() =
getSystemService(Context.WINDOW_SERVICE)
as WindowManager
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WindowManager
fun Context.getWindowManager() =
getSystemService(Context.WINDOW_SERVICE)
as WindowManager
val windowManager = getWindowManager()
val display = windowManager.getDefaultDisplay()
val width = display.width
val height = display.height
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Extension Properties
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WindowManager
fun Context.getWindowManager() =
getSystemService(Context.WINDOW_SERVICE)
as WindowManager
val windowManager = getWindowManager()
val display = windowManager.getDefaultDisplay()
val width = display.width
val height = display.height
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WindowManager
val Context.windowManager =
get() =
getSystemService(Context.WINDOW_SERVICE)
as WindowManager
val windowManager = getWindowManager()
val display = windowManager.getDefaultDisplay()
val width = display.width
val height = display.height
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WindowManager
val Context.windowManager =
get() =
getSystemService(Context.WINDOW_SERVICE)
as WindowManager
val display = windowManager.getDefaultDisplay()
val width = display.width
val height = display.height
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Extends Library
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Glide Extension
http://www.example.com/12345?width=300&height=300
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Glide Extension
http://www.example.com/12345?width=300&height=300
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Glide Extension
fun RequestManager.loadOptimize(url: String?, width: Int, height: Int):
DrawableTypeRequest =
load(url?.let {
"$it?width=$width&height=$height"
})
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Glide Extension
fun RequestManager.loadOptimize(url: String?, width: Int, height: Int):
DrawableTypeRequest =
load(url?.let {
"$it?width=$width&height=$height"
})
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Glide Extension
fun RequestManager.loadOptimize(url: String?, width: Int, height: Int):
DrawableTypeRequest =
load(url?.let {
"$it?width=$width&height=$height"
})
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Glide Extension
fun RequestManager.loadOptimize(url: String?, width: Int, height: Int):
DrawableTypeRequest =
load(url?.let {
"$it?width=$width&height=$height"
})
Glide.with(context)
.loadOptimize(url, 300, 300)
.into(imageView)
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Listener
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addOnPageChangeListener
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ViewPager#
OnPageChangeListener(Java)
pager.addOnPageChangeListener(new OnPageChangeListener() {
@Override
public void onPageSelected(int position) {
// no op
}
@Override
public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
// no op
}
@Override
public void onPageScrollStateChanged(int state) {
onStateChange(state);
}
});
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ViewPager#
OnPageChangeListener(Java)
pager.addOnPageChangeListener(new OnPageChangeListener() {
@Override
public void onPageSelected(int position) {
// no op
}
@Override
public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
// no op
}
@Override
public void onPageScrollStateChanged(int state) {
onStateChange(state);
}
});
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ViewPager#
OnPageChangeListener(Java)
pager.addOnPageChangeListener(new OnPageChangeListener() {
@Override
public void onPageSelected(int position) {
// no op
}
@Override
public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
// no op
}
@Override
public void onPageScrollStateChanged(int state) {
onStateChange(state);
}
});
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fun ViewPager.addOnPageChangeListener(
onPageScrolled: (position: Int, positionOffset: Float, positionOffsetPixels: Int) -> Unit = {
position, positionOffset, positionOffsetPixels ->
},
onPageScrollStateChanged: (state: Int) -> Unit = {},
onPageSelected: (position: Int) -> Unit = {}
) = addOnPageChangeListener(object : ViewPager.OnPageChangeListener {
override fun onPageScrolled(position: Int, positionOffset: Float, positionOffsetPixels: Int) {
onPageScrolled(position, positionOffset, positionOffsetPixels)
}
override fun onPageScrollStateChanged(state: Int) {
onPageScrollStateChanged(state)
}
override fun onPageSelected(position: Int) {
onPageSelected(position)
}
})
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OnPageChangeListener(Java)
pager.addOnPageChangeListener(new OnPageChangeListener() {
@Override
public void onPageSelected(int position) {
// no op
}
@Override
public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
// no op
}
@Override
public void onPageScrollStateChanged(int state) {
onStateChange(state);
}
});
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Extends
addOnPageChangeListener
pager.addOnPageChangeListener(onPageScrollStateChanged = {
onStateChange(state)
})
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Extends
addOnPageChangeListener
pager.addOnPageChangeListener(onPageScrollStateChanged = {
onStateChange(state)
})
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Animator
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Animator(Java)
anim.addListener(new AnimatorListener() {
...
@Override
public void onAnimationEnd(Animator animation) {
animDrawable.stop()
}
...
});
anim.setDuration(300)
.start();
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Animator
fun Animator.addListener(
onAnimationStart: (Animator) -> Unit = {},
onAnimationEnd: (Animator) -> Unit = {},
onAnimationCancel: (Animator) -> Unit = {},
onAnimationRepeat: (Animator) -> Unit = {}): Animator {
addListener(object : Animator.AnimatorListener {
override fun onAnimationStart(animation: Animator) {
onAnimationStart(animation)
}
// …..
})
return this
}
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Animator
fun Animator.addListener(
onAnimationStart: (Animator) -> Unit = {},
onAnimationEnd: (Animator) -> Unit = {},
onAnimationCancel: (Animator) -> Unit = {},
onAnimationRepeat: (Animator) -> Unit = {}): Animator {
addListener(object : Animator.AnimatorListener {
override fun onAnimationStart(animation: Animator) {
onAnimationStart(animation)
}
// …..
})
return this
}
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Animator
fun Animator.addListener(
onAnimationStart: (Animator) -> Unit = {},
onAnimationEnd: (Animator) -> Unit = {},
onAnimationCancel: (Animator) -> Unit = {},
onAnimationRepeat: (Animator) -> Unit = {}): Animator {
addListener(object : Animator.AnimatorListener {
override fun onAnimationStart(animation: Animator) {
onAnimationStart(animation)
}
// …..
})
return this
}
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Animator
anim
.addListener(onAnimationEnd = { animDrawable.stop() })
.setDuration(300)
.start();
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Animator
anim
.addListener(onAnimationEnd = { animDrawable.stop() })
.setDuration(300)
.start();
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Thank you !!