Creating Great APIs With Kotlin

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Creating Great APIs With Kotlin David Tiago Conceição Involves Android Dev BR @davidtiagocon

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Android Development if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) { return context.getResources() .getColor(colorId, context.getTheme()); } else { return context.getResources() .getColor(colorId); }

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Android Development public final class ColorUtils { @ColorInt public static int getColor( Context context, @ColorRes int colorId) { if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) { return context.getResources() .getColor(colorId, context.getTheme()); } else { return context.getResources() .getColor(colorId); } } }

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Android Development ColorUtils.getColor(context, R.color.primary_regular)

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Android Development context.getThemedColor(context, R.color.primary_regular)

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Android Development

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Extension Functions @ColorInt fun Context.getThemedColor(@ColorRes colorId: Int) = if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) { this.resources.getColor(colorId, this.theme) } else { this.resources.getColor(colorId) }

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Extension Functions

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Extension Functions public final class ContextExtensionsKt { @ColorInt public static final int getThemedColor(@NotNull Context $this$getThemedColor, @ColorRes int colorId) { return Build.VERSION.SDK_INT >= 23 ? $this$getThemedColor.getResources().getColor(colorId, $this$getThemedColor.getTheme()) : $this$getThemedColor.getResources().getColor(colorId); } }

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Extension Functions ContextExtensionsKt.getThemedColor(context, -500071)

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Extension Functions @ColorInt inline fun Context.getThemedColor(@ColorRes colorId: Int) = if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) { this.resources.getColor(colorId, this.theme) } else { this.resources.getColor(colorId) }

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Extension Functions var10000 = VERSION.SDK_INT >= 23 ? context.getResources().getColor(colorId$iv, context.getTheme()) : context.getResources().getColor(colorId$iv);

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Extension Functions useCase.execute(id, date) .lastElement() .test() .assertDefaultData(pointOfSaleNameFromItinerary) .assertExpectedState(state)

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Extension Functions useCase.execute(id, date) .lastElement() .test() .assertDefaultData(pointOfSaleNameFromItinerary) .assertExpectedState(state) private fun TestObserver.assertExpectedState( expectedState: SomeInternalState): TestObserver { assertValue { it.someInternalState == expectedState } return this }

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Extension Properties val List.lastIndex: Int get() = size - 1

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“Extension based development” Less Utils Less hierarchies More extensions Extensions

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Kotlin Android Extensions Android KTX Extension Libraries

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animation.setAnimationListener(new Animation.AnimationListener() { @Override public void onAnimationEnd(Animation animation) { onViewShowed(); } @Override public void onAnimationStart(Animation animation) {} @Override public void onAnimationRepeat(Animation animation) {} }); Arguments

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fun Animation.listener( onAnimationStart: ((Animation) -> Unit)? = null, onAnimationEnd: ((Animation) -> Unit)? = null, onAnimationRepeat: ((Animation) -> Unit)? = null) { ... Default Arguments

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fun Animation.listener( onAnimationStart: ((Animation) -> Unit)? = null, onAnimationEnd: ((Animation) -> Unit)? = null, onAnimationRepeat: ((Animation) -> Unit)? = null) { this.setAnimationListener(object : Animation.AnimationListener { override fun onAnimationRepeat(animation: Animation?) { onAnimationStart?.invoke(animation!!) ... Default Arguments

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animation.listener(onAnimationEnd = { onViewShowed()}) Named Arguments

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data class ClassWithManyIntegers( val integerProperty: Int = 0, val anotherIntegerProperty: Int = 0, val someExtraIntegerProperty: Int = 0) Builders

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data class ClassWithManyIntegers( val integerProperty: Int = 0, val anotherIntegerProperty: Int = 0, val someExtraIntegerProperty: Int = 0) val complexInstance = ClassWithManyIntegers() Builders

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data class ClassWithManyIntegers( val integerProperty: Int = 0, val anotherIntegerProperty: Int = 0, val someExtraIntegerProperty: Int = 0) val complexInstance = ClassWithManyIntegers( someExtraIntegerProperty = 10) Builders

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val firstPoint = Point(10, 10) val secondPoint = Point(20, 20) Operations

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val firstPoint = Point(10, 10) val secondPoint = Point(20, 20) val firstX = firstPoint.x val firstY = firstPoint.y val secondX = secondPoint.x val secondY = secondPoint.y val plusPoint = Point(firstX + secondX, secondY + secondY) Operations

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val firstPoint = Point(10, 10) val secondPoint = Point(20, 20) val plusPoint = firstPoint + secondPoint Operations

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val firstPoint = Point(10, 10) val secondPoint = Point(20, 20) val plusPoint = firstPoint + secondPoint operator fun Point.plus(another: Point) = Point(x + another.x, y + another.y) Operators

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val (x,y) = firstPoint Operators

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val (x,y) = firstPoint operator fun Point.component1() = x operator fun Point.component2() = y Operators

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val viewGroup: ViewGroup = getViewGroup() viewGroup.addView(view) Operators

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val viewGroup: ViewGroup = getViewGroup() viewGroup += view Operators

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val viewGroup: ViewGroup = getViewGroup() viewGroup += view operator fun ViewGroup.plusAssign(view: View) = addView(view) Operators

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val view = viewGroup[0] Operators

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val view = viewGroup[0] operator fun ViewGroup.get(index: Int): View? = getChildAt(index) Operators

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for (index in 0 until viewGroup.childCount) { doSomething(viewGroup.getChildAt(index)) } Functions

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for (index in 0 until viewGroup.childCount) { doSomething(viewGroup.getChildAt(index)) } viewGroup.forEach { view -> doSomething(view) } Functions

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viewGroup.forEach { view -> doSomething(view) } fun ViewGroup.forEach(onEach: (View) -> Unit) { for (index in 0 until childCount) { onEach(getChildAt(index)) } } Functions

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viewGroup.forEach { view -> doSomething(view) } fun ViewGroup.forEach(onEach: (View) -> Unit) { for (index in 0 until childCount) { onEach(getChildAt(index)) } } Functions

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runInDatabaseTransaction { // Some database stuff } Functions

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fun runInDatabaseTransaction(databaseFunction: (SQLiteDatabase) -> Unit) { val dataBase = getDatabase() try { dataBase.beginTransaction() databaseFunction(dataBase) dataBase.setTransactionSuccessful() } finally { dataBase.endTransaction() } Functions

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for (index in 0 until viewGroup.childCount) { doSomething(viewGroup.getChildAt(index)) } Functions

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/** Returns a range from this value up to but excluding the specified [to] value. * If the [to] value is less than or equal to `this` value, then the returned range is empty.*/ public infix fun Int.until(to: Int): IntRange { if (to <= Int.MIN_VALUE) return IntRange.EMPTY return this .. (to - 1).toInt() } Functions

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val untilRange = 0 until 10 val untilCharRange = 'a' until 'z' val downProgression = 10 downTo 0 Functions

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//Mockk every { saveEvent(any(), any()) } returns Unit every { mock invoke "openDoor" withArguments listOf("left", "rear") } returns "OK" verify { sendMessageHandler wasNot Called } DSLs

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//Mockk infix fun returns(returnValue: T) = answers(ConstantAnswer(returnValue)) DSLs

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class Loading class Error class Success class ViewModel { var currentState: Any = Loading() } State

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open class PossibleState class Loading : PossibleState() class Error : PossibleState() class Success : PossibleState() class ViewModel { var currentState: PossibleState = Loading() } State

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sealed class PossibleState { object Loading : PossibleState() object Error : PossibleState() object Success : PossibleState()} class ViewModel { var currentState: PossibleState = PossibleState.Loading } Sealed Classes

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class Scheduler { fun schedule(delay: Long, action: () -> Unit) { //... } } Argument Types

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class Scheduler { fun schedule( delay: Long, timeUnit: TimeUnit, action: () -> Unit) { //... } } Argument Types

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class Minutes(val value: Long) class Scheduler { fun schedule( delay: Minutes, action: () -> Unit) { //... } } Argument Types

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inline class Minutes(val value: Long) class Scheduler { fun schedule( delay: Minutes, action: () -> Unit) { //... } } Inline classes

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Extensions Named and Default arguments Operators Higher order functions Inﬁx DSLs Sealed classes Inline classes Wrapping up

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How to know more? ● Extensions: kotlinlang.org/docs/reference/extensions.html ● Kotlin Android Extensions: kotlinlang.org/docs/tutorials/android-plugin.html ● Android KTX: developer.android.com/kotlin/ktx ● Keywords and Operators: kotlinlang.org/docs/reference/keyword-reference.html ● Functions: kotlinlang.org/docs/reference/functions.html ● MockK: mockk.io ● Sealed Classes: kotlinlang.org/docs/reference/sealed-classes.html ● KotlinConf 2018 - Representing State: the Kotlin Edition by Christina Lee: www.youtube.com/watch?v=-lVVfxsRjcY ● Inline classes: kotlinlang.org/docs/reference/inline-classes.html

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slack.AndroidDevBR.org Android Dev BR

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Thank you! David Tiago Conceição [email protected] Android Dev BR @davidtiagoconceicao twitter.com/@davidtiagocon speakerdeck.com/davidtcdeveloper