10 Extension Functions of Kotlin in Android Development

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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 = android.R.id.content) = supportFragmentManager .beginTransaction() .add(containerId, fragment) .commit() setFragment(MainFragment.newInstance(), android.R.id.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 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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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 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 !!