Kotlin for Android: Starting out with confidence

An Introduction to Kotlin for Android Developers presented at GDG Uyo IO Extended Conference

Transcript

1. Kotlin for Android Starting out with confdence Ememobong Akpanekpo @emem_akpanekpo
2. What is Kotlin?
3. What is Kotlin?
4. Why Learn Kotlin?
5. My Journey
6. Google I/O 2017 - Kotlin Support Announcement
7. In my mind
8. I tried Kotlin Developer site
9. try.kotlinlang.org
10. I tried an Online Co
11. Udemy
12. I stole a Kotlin book
14. This one was also awesome Though I never fnished it
16. I decided to CMD +ALT+ SHIFT + K a few fles
18. Eventually I decided to just try write Kotlin code
19. You don’t need to know all the features to write Kotlin code. Learn as you go.
20. Kotlin Things
21. Semicolons - there are none *well unless you want them
22. var / val
23. var = variable value
24. val = constant value
25. var temperature : Int = 1 // has type Int val numberMembers = 5 //automatically inferred type Int val percentage = 80 / 100 percentage = 30 //does not compile var percentage = 80 / 100 percentage = 30 //compiles
26. var temperature : Int = 1 // has type Int val numberMembers = 5 //automatically inferred type Int val percentage = 80 / 100 percentage = 30 //does not compile var percentage = 80 / 100 percentage = 30 //compiles
27. var temperature : Int = 1 // has type Int val numberMembers = 5 //automatically inferred type Int val percentage = 80 / 100 percentage = 30 //does not compile var percentage = 80 / 100 percentage = 30 //compiles
28. var temperature : Int = 1 // has type Int val numberMembers = 5 //automatically inferred type Int val percentage = 80 / 100 percentage = 30 //does not compile var percentage = 80 / 100 percentage = 30 //compiles
29. Nullability
30. The Kotlin Type system distinguishes between references that can hold null and those that can not
31. Avoid NullPointerException *well unless you want them
32. //No Nulls Allowed var average : Double = 1.0 average = 2.0 average = null
33. //No Nulls Allowed var average : Double = 1.0 average = 2.0 average = null //Allows nulls var average : Double? = 1.0 average = 2.0 average = null
34. // Double !! -> NullPointerException val l = name!!.length // Safe Call ?. with chains val name = bob?.department?.head?.name // Elvis Operator val length = b?.length ?: -1
35. // Double Bang !! -> NullPointerException val l = b!!.length // Safe Call ?. with chains val name = bob?.department?.head?.name // Elvis Operator val length = b?.length ?: -1
36. // Double Bang !! -> NullPointerException val l = b!!.length // Safe Call ?. with chains val name = bob?.department?.head?.name // Elvis Operator ?: val length = b?.length ?: -1
37. val name : String? = "hello" name?.let { //Now name is not null at this point textView.text = name } // There are whole bunch more - .with{} .run{} - with slight diferences // Can also just do a normal null check!
38. lateinit
39. class EventsActivity : AppCompatActivity() { private lateinit var recyclerViewAdapter: SimpleAdapter override fun onCreate(savedInstanceState: Bundle?) { // Other initialization stuf recyclerViewAdapter = SimpleAdapter(/*..*/) } }
40. lazy
41. val lazyValue: String by lazy { println("computed!") "Hello" } fun main(args: Array<String>) { println(lazyValue) println(lazyValue) } computed! Hello Hello
42. when
43. when (s) { 1 -> print("x == 1") 2 -> print("x == 2") else -> { // Note the block print("x is neither 1 nor 2") } }
44. enum class Currency { GBP, ZAR; } when (currency) { Currency.GBP -> doSomething() Currency.ZAR -> doAnotherThing() }
45. enum class Currency { GBP, USD, ZAR; } when (currency) { Currency.GBP -> doSomething() Currency.ZAR -> doAnotherThing() }
46. enum class Currency { GBP, USD, ZAR; } when (currency) { Currency.GBP -> doSomething() Currency.ZAR -> doAnotherThing() else -> doNothing() }
47. Functions
48. Functions are frst-class c
49. fun calculateSum(a: Int, b: Int) : Int { return a + b } fun calculateSum(a: Int, b: Int) = a + b
50. fun calculateSum(a: Int, b: Int) : Int { return a + b } fun calculateSum(a: Int, b: Int) = a + b
51. Extension Functions
52. fun String.hello(): String = "Hello " + this // use the new hello() method val hi = "Kotlin !".hello() Hello Kotlin ! fun TextView.getFloatValue() : Float { return 0f } val foat = textViewHello.getFloatValue()
53. fun String.hello(): String = "Hello " + this // use the new hello() method val hi = "Kotlin !".hello() Hello Kotlin ! fun TextView.getFloatValue() : Float { return 0f } val num = textViewHello.getFloatValue()
54. Default Values
55. fun calculateSum(a: Int = 2, b: Int) : Int { return a + b } val sum = calculateSum(b = 3) 5 //Can be done on Constructors as well as functions
56. Higher Order Functions & Lambdas
57. val exampleArray = arrayListOf(3,324,5,6,3,2,6,8,1,2,4,3,2) exampleArray.flter { it % 2 == 0 } [324, 6, 2, 6, 8, 2, 4, 2] val numberList = arrayListOf(1,2,3,4,5,6,7,8,9) numberList.map { it * 2 } .flter { it % 3 == 0} [6, 12, 18]
58. val exampleArray = arrayListOf(3,324,5,6,3,2,6,8,1,2,4,3,2) exampleArray.flter { it % 2 == 0 } [324, 6, 2, 6, 8, 2, 4, 2] val numberList = arrayListOf(1,2,3,4,5,6,7,8,9) numberList.map { it * 2 } .flter { it % 3 == 0} [6, 12, 18]
59. fun calcPercentage(value: Int, onComplete: (output : Double) -> Unit) { val calculation = value / 100.0 onComplete(calculation) } //called in onCreate or wherever calculatePercentage(2) { Log.d("MainActivity", "Calculation Complete: $it") } Calculation Complete: 0.02
60. fun calcPercentage(value: Int, onComplete: (input : Double) -> Unit) { val calculation = value / 100.0 onComplete(calculation) } //called in onCreate or wherever calcPercentage(2) { Log.d("MainActivity", "Calculation Complete: $it") } Calculation Complete: 0.02
61. fun <T> executeWork(job: () -> T) : T { Log.d(TAG, "Work started") val result = job() Log.d(TAG, "Work Fin") return result } val number = executeWork { 100 * 5 } Log.d(TAG, "Result: $number") val stringCalc = executeWork { "Rebecca".plus(" Hello") } Log.d(TAG, "String: $stringCalc") Work started Work Fin Result: 500 Work started Work Fin String: Rebecca Hello
62. fun <T> executeWork(job: () -> T) : T { Log.d(TAG, "Work started") val result = job() Log.d(TAG, "Work Fin") return result } val number = executeWork { 100 * 5 } Log.d(TAG, "Result: $number") val stringCalc = executeWork { "Rebecca".plus(" Hello") } Log.d(TAG, "String: $stringCalc") Work started Work Fin Result: 500 Work started Work Fin String: Rebecca Hello
63. fun <T> executeWork(job: () -> T) : T { Log.d(TAG, "Work started") val result = job() Log.d(TAG, "Work Fin") return result } val number = executeWork { 100 * 5 } Log.d(TAG, "Result: $number") val stringCalc = executeWork { "Rebecca".plus(" Hello") } Log.d(TAG, "String: $stringCalc") Work started Work Fin Result: 500 Work started Work Fin String: Rebecca Hello
64. Classes
65. class Admin : User { val name: String val age: Int constructor(name : String, age : Int){ this.name =name this.age = age } fun isAdult(): Boolean { return age >= 18 } }
66. class Admin(val name: String, val age: Int) : User { fun isAdult(): Boolean { return age >= 18 } }
67. class Admin(val name: String, val age: Int) : User { fun isAdult() = age >= 18 }
68. Data Classes
69. // data classes data class Admin(val name: String, val age: Int) // Automatically generates: - toString() - hashCode() / equals() - copy()
70. Coroutines *Experimental
71. Simplify Async Programming Lightweight thread *Spin up 1mil coroutines easily
72. Coroutines are computations that can be suspended without blocking a thread. https://kotlinlang.org/docs/tutorials/coroutines-basic-jvm.html
73. //onCreate job = launch(background) { val result = requestData() launch(UI) { textViewHello.text = result } } //suspend function suspend fun requestData(): String { delay(3000) return "DONE" } //onDestroy job.cancel()
74. //onCreate job = launch(background) { val result = requestData() launch(UI) { textViewHello.text = result } } //suspend function suspend fun requestData(): String { delay(3000) return "DONE" } //onDestroy job.cancel()
75. //onCreate job = launch(background) { val result = requestData() launch(UI) { textViewHello.text = result } } //suspend function suspend fun requestData(): String { delay(3000) return "DONE" } //onDestroy job.cancel()
76. https://kotlinlang.org/docs/tutorials/c oroutines-basic-jvm.html
77. Android KTX
78. github.com/android/android-ktx
79. A set of Kotlin extensions for Android
80. //Before sharedPreferences.edit() .putBoolean("key", value) .apply() //After - with Android KTX sharedPreferences.edit { putBoolean("key", value) }
81. //Before view.viewTreeObserver.addOnPreDrawListener( object : ViewTreeObserver.OnPreDrawListener { override fun onPreDraw(): Boolean { viewTreeObserver.removeOnPreDrawListener(this) actionToBeTriggered() return true } }) //After - with Android KTX view.doOnPreDraw { actionToBeTriggered() }
82. val (a,r,g,b) = Color.MAGENTA val drawable = customDrawable.toBitmap() canvas.withTranslation(x, y) { // block } val (year, month, day) = LocalDate.now()
83. The difcult bits *for me...
84. Mocking - All classes in Kotlin are final unless you tell it otherwise (ie mark it as open ) - Workarounds but seem unnecessary https://antonioleiva.com/mockito-2-kotlin/ http://hadihariri.com/2016/10/04/Mocking-Kotlin-With-Mockito/
85. Tooling IntelliJ is great… but it doesn’t write all the code. Battled with Lambda syntax, it sometimes doesn’t fll in all the blanks nicely Solution - Write it in Java, then copy paste the java into your Kotlin fle and it’ll auto convert
86. Nothing, Unit & Any Nothing - never returns - ie infnite loop or exception throwing Unit - default return type for a function Any - Default Super Type (similar to Java’s Object type) http://natpryce.com/articles/000818.html
87. Resources
88. Online Courses O’Reilly Introduction to Kotlin Udacity Kotlin Course https://www.youtube.com/reUdsults?search_query=Kotlin+on+Android
89. Practise Kotlin Koans https://try.kotlinlang.org Kotlin REPL Kotlin Android Codelab
90. try.kotlinlang.org
93. Books • Kotlin in Action - Svetlana Isakova - Dmitry Jemerov • Kotlin for Android Developers - Some common patterns etc
94. Online Community kotlinweekly.net talkingkotlin.com reddit.com/r/kotlin
95. Just start writing Kotlin code
96. Thank you! Questions? Ememobong Akpanekpo @emem_akpanekpo