Creating Great APIs With Kotlin

Slides from my talk at Kotlin/Everywhere Floripa:

https://www.meetup.com/GDGFloripa/events/262037183/

Transcript

1. Creating Great APIs With Kotlin David Tiago Conceição Involves Android Dev BR @davidtiagocon
2. Android Development if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) { return context.getResources() .getColor(colorId, context.getTheme()); } else { return context.getResources() .getColor(colorId); }
3. 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); } } }
4. Android Development ColorUtils.getColor(context, R.color.primary_regular)
5. Android Development context.getThemedColor(context, R.color.primary_regular)
6. Android Development
7. 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) }
8. 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) }
9. Extension Functions
10. 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); } }
11. 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); } }
12. Extension Functions ContextExtensionsKt.getThemedColor(context, -500071)
13. 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) }
14. Extension Functions var10000 = VERSION.SDK_INT >= 23 ? context.getResources().getColor(colorId$iv, context.getTheme()) : context.getResources().getColor(colorId$iv);
15. Extension Functions useCase.execute(id, date) .lastElement() .test() .assertDefaultData(pointOfSaleNameFromItinerary) .assertExpectedState(state)
16. Extension Functions useCase.execute(id, date) .lastElement() .test() .assertDefaultData(pointOfSaleNameFromItinerary) .assertExpectedState(state) private fun TestObserver<State>.assertExpectedState( expectedState: SomeInternalState): TestObserver<State> { assertValue { it.someInternalState == expectedState } return this }
17. Extension Properties val <T> List<T>.lastIndex: Int get() = size - 1
18. “Extension based development” Less Utils Less hierarchies More extensions Extensions
19. Kotlin Android Extensions Android KTX Extension Libraries
20. 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
21. 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
22. fun Animation.listener( onAnimationStart: ((Animation) -> Unit)? = null, onAnimationEnd: ((Animation) -> Unit)? = null, onAnimationRepeat: ((Animation) -> Unit)? = null) { ... Default Arguments
23. 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
24. animation.listener(onAnimationEnd = { onViewShowed()}) Named Arguments
25. data class ClassWithManyIntegers( val integerProperty: Int = 0, val anotherIntegerProperty: Int = 0, val someExtraIntegerProperty: Int = 0) Builders
26. data class ClassWithManyIntegers( val integerProperty: Int = 0, val anotherIntegerProperty: Int = 0, val someExtraIntegerProperty: Int = 0) val complexInstance = ClassWithManyIntegers() Builders
27. data class ClassWithManyIntegers( val integerProperty: Int = 0, val anotherIntegerProperty: Int = 0, val someExtraIntegerProperty: Int = 0) val complexInstance = ClassWithManyIntegers( someExtraIntegerProperty = 10) Builders
28. val firstPoint = Point(10, 10) val secondPoint = Point(20, 20) Operations
29. 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
30. val firstPoint = Point(10, 10) val secondPoint = Point(20, 20) val plusPoint = firstPoint + secondPoint Operations
31. 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
32. val (x,y) = firstPoint Operators
33. val (x,y) = firstPoint operator fun Point.component1() = x operator fun Point.component2() = y Operators
34. val viewGroup: ViewGroup = getViewGroup() viewGroup.addView(view) Operators
35. val viewGroup: ViewGroup = getViewGroup() viewGroup += view Operators
36. val viewGroup: ViewGroup = getViewGroup() viewGroup += view operator fun ViewGroup.plusAssign(view: View) = addView(view) Operators
37. val view = viewGroup[0] Operators
38. val view = viewGroup[0] operator fun ViewGroup.get(index: Int): View? = getChildAt(index) Operators
39. for (index in 0 until viewGroup.childCount) { doSomething(viewGroup.getChildAt(index)) } Functions
40. for (index in 0 until viewGroup.childCount) { doSomething(viewGroup.getChildAt(index)) } viewGroup.forEach { view -> doSomething(view) } Functions
41. viewGroup.forEach { view -> doSomething(view) } fun ViewGroup.forEach(onEach: (View) -> Unit) { for (index in 0 until childCount) { onEach(getChildAt(index)) } } Functions
42. viewGroup.forEach { view -> doSomething(view) } fun ViewGroup.forEach(onEach: (View) -> Unit) { for (index in 0 until childCount) { onEach(getChildAt(index)) } } Functions
43. runInDatabaseTransaction { // Some database stuff } Functions
44. fun runInDatabaseTransaction(databaseFunction: (SQLiteDatabase) -> Unit) { val dataBase = getDatabase() try { dataBase.beginTransaction() databaseFunction(dataBase) dataBase.setTransactionSuccessful() } finally { dataBase.endTransaction() } Functions
45. for (index in 0 until viewGroup.childCount) { doSomething(viewGroup.getChildAt(index)) } Functions
46. /** 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
47. val untilRange = 0 until 10 val untilCharRange = 'a' until 'z' val downProgression = 10 downTo 0 Functions
48. //Mockk every { saveEvent(any(), any()) } returns Unit every { mock invoke "openDoor" withArguments listOf("left", "rear") } returns "OK" verify { sendMessageHandler wasNot Called } DSLs
49. //Mockk infix fun returns(returnValue: T) = answers(ConstantAnswer(returnValue)) DSLs
50. class Loading class Error class Success class ViewModel { var currentState: Any = Loading() } State
51. open class PossibleState class Loading : PossibleState() class Error : PossibleState() class Success : PossibleState() class ViewModel { var currentState: PossibleState = Loading() } State
52. sealed class PossibleState { object Loading : PossibleState() object Error : PossibleState() object Success : PossibleState()} class ViewModel { var currentState: PossibleState = PossibleState.Loading } Sealed Classes
53. class Scheduler { fun schedule(delay: Long, action: () -> Unit) { //... } } Argument Types
54. class Scheduler { fun schedule( delay: Long, timeUnit: TimeUnit, action: () -> Unit) { //... } } Argument Types
55. class Minutes(val value: Long) class Scheduler { fun schedule( delay: Minutes, action: () -> Unit) { //... } } Argument Types
56. inline class Minutes(val value: Long) class Scheduler { fun schedule( delay: Minutes, action: () -> Unit) { //... } } Inline classes
57. Extensions Named and Default arguments Operators Higher order functions Infix DSLs Sealed classes Inline classes Wrapping up
58. 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
59. slack.AndroidDevBR.org Android Dev BR
60. Thank you! David Tiago Conceição david.tiago@involves.com.br Android Dev BR @davidtiagoconceicao twitter.com/@davidtiagocon speakerdeck.com/davidtcdeveloper