Streamline your Android app API with Kotlin

Since May of 2017, Kotlin became officially acknowledged by Google and promoted to first class citizen when we talk about native Android application development.

Android framework is fully written in Java, which means that in its core there is a lot of APIs that are robust and not so easy/straightforward to use. In this talk, we'll go through tips and tricks how Kotlin can help us to streamline those API-s in our apps and make the code more readable and more easy to use.

Transcript

1. Streamline your Android app API with Kotlin Nebojša Vukšić
 @TheTechW0lf 1
2. SHORT OVERVIEW OF ANDROID HISTORY 2
3. SHORT OVERVIEW OF ANDROID HISTORY 3 2008
 Initial launch 2009 2016 2010 2011 2012 2013 2014 2015 2017 2018
4. 4 2008
 Initial launch 2016 2009 2010 2011 2012 2013 2014 2015 2017 2018 SHORT OVERVIEW OF ANDROID HISTORY
5. 5 2008 2016 2009 Cupcake
 Donut
 Eclair 2010 Froyo
 Gingerbread 2011 Honeycomb 
 Ice Cream Sandwich 2012 Jelly Bean 2013 2014 2015 2017 2018 SHORT OVERVIEW OF ANDROID HISTORY
6. 6 2008 2016 2009 2010 2011 2012 2013 KitKat 2014 2015 2017 2018 SHORT OVERVIEW OF ANDROID HISTORY
7. 7 2008 2016 2009 2010 2011 2012 2013 2014
 Lollipop 2015 2017 2018 SHORT OVERVIEW OF ANDROID HISTORY
8. 8 2008 2016 2009 2010 2011 2012 2013 2014
 Lollipop 2015 2017 2018 SHORT OVERVIEW OF ANDROID HISTORY
9. 9 2008 2016 2009 2010 2011 2012 2013 2014
 Lollipop 2015 2017 2018 SHORT OVERVIEW OF ANDROID HISTORY
10. We are stuck in Java 7 world (few Java 8 features supported by platform) Android API ceremony Unable to extend Android platform types 10 Those backend devs are lucky ☹
11. 11 2008 2016 2009 2010 2011 2012 2013 2014
 Lollipop 2015 2017 2018 SHORT OVERVIEW OF ANDROID HISTORY
12. 12 2008 2016 2009 2010 2011 2012 2013 2014
 Lollipop 2015 2017 2018 SHORT OVERVIEW OF ANDROID HISTORY
13. 13 2008 2016 2009 2010 2011 2012 2013 2014
 Lollipop 2015 2017 2018 SHORT OVERVIEW OF ANDROID HISTORY
14. 14 2008 2016 2009 2010 2011 2012 2013 2014
 Lollipop 2015 2017 2018 7.5 SHORT OVERVIEW OF ANDROID HISTORY
15. 15 2008 2016 2009 2010 2011 2012 2013 2014
 Lollipop 2015 2017 2018 SHORT OVERVIEW OF ANDROID HISTORY
16. 16 2008 2016 Nougat 2009 2010 2011 2012 2013 2014 2015
 Marshmallow 2017 Oreo 2018 SHORT OVERVIEW OF ANDROID HISTORY
17. 17 2008 2016 Nougat 2009 2010 2011 2012 2013 2014 2015
 Marshmallow 2017 Oreo 2018 SHORT OVERVIEW OF ANDROID HISTORY
19. JVM language interoperable with Java 1 Allows extensions of the platform types Provides higher order functions on collections Type safety built in type system Many other modern language features 2 3 4 5 Kotlin 19
20. SHORT HISTORY OF ANDROID 20 2008 2016 Nougat 2009 2010 2011 2012 2013 2014 2015
 Marshmallow 2017 Oreo 2018
21. SHORT HISTORY OF ANDROID 21 2008 2016 Nougat 2009 2010 2011 2012 2013 2014 2015
 Marshmallow 2017 Oreo 2018
22. SHORT HISTORY OF ANDROID 22 2016 Nougat 2012 2013 2014
 Lollipop 2015
 Marshmallow 2017 Oreo 2018 2019
23. SHORT HISTORY OF ANDROID 23 2016 2012 2013 2014 2015 2017 2018 Pie 2019 Q
25. 25 „Android is becoming increasingly Kotlin first platform“ Chat Haase at Google I/O 19
26. Enough of talking, let’s code! 26
27. 27 View.VISIBLE View.INVISIBLE View.GONE View visibility API constants
30. 30 View.VISIBLE View.INVISIBLE View.GONE View visibility api constants
31. if(screen.requiresSearchIcon) { searchIcon.visibility = View.VISIBLE } else { searchIcon.visibility = View.GONE } 31 class Screen(…, val requiresSearchIcon: Boolean, …)
32. { } { } if(screen.requiresSearchIcon) { searchIcon.visibility = View.VISIBLE } else { searchIcon.visibility = View.GONE } 32 class Screen(…, val requiresSearchIcon: Boolean, …)
33. 33 searchIcon.visibility = if(screen.requiresSearchIcon) { View.VISIBLE } else { View.GONE } class Screen(…, val requiresSearchIcon: Boolean, …)
34. searchIcon.isVisible 34 class Screen(…, val requiresSearchIcon: Boolean, …) val View.isVisible: Boolean get() = visibility == View.VISIBLE set(isVisible) { visibility = if(isVisible) View.VISIBLE else View.GONE } searchIcon.visibility = if(screen.requiresSearchIcon) { View.VISIBLE } else { View.GONE }
35. searchIcon.isVisible = screen.requiresSearchIcon class Screen(…, val requiresSearchIcon: Boolean, …) 35 val View.isVisible: Boolean get() = visibility == View.VISIBLE set(isVisible) { visibility = if(isVisible) View.VISIBLE else View.GONE }
36. setPadding( paddingTop, paddingBottom sessionTitleView.setPadding( 10, message.paddingTop, 10, message.paddingBottom) 36
37. inline fun View.updatePadding( left: Int = paddingLeft, top: Int = paddingTop, right: Int = paddingRight, bottom: Int = paddingBottom ) { setPadding(left, top, right, bottom) } sessionTitleView.setPadding( 10, message.paddingTop, 10, message.paddingBottom) 37
38. inline fun View.updatePadding( left: Int = paddingLeft, top: Int = paddingTop, right: Int = paddingRight, bottom: Int = paddingBottom ) { setPadding(left, top, right, bottom) } inline fun View.updatePadding( left: Int = paddingLeft, top: Int = paddingTop, right: Int = paddingRight, bottom: Int = paddingBottom ) { setPadding(left, top, right, bottom) } sessionTitleView.setPadding( 10, message.paddingTop, 10, message.paddingBottom) 38
39. inline fun View.updatePadding( left: Int = paddingLeft, top: Int = paddingTop, right: Int = paddingRight, bottom: Int = paddingBottom ) { setPadding(left, top, right, bottom) } sessionTitleView.updatePadding(left = 10, right = 10) 39
40. inline fun View.updatePadding( left: Int = paddingLeft, top: Int = paddingTop, right: Int = paddingRight, bottom: Int = paddingBottom ) { setPadding(left, top, right, bottom) } sessionTitleView.updatePadding(left = 10, right = 10) 40 inline fun View.updatePadding( left: Int = paddingLeft, top: Int = paddingTop, right: Int = paddingRight, bottom: Int = paddingBottom ) { setPadding(left, top, right, bottom) }
41. sessionTitleView.updatePadding(left = 10, right = 10) 41 Byte code: int leftPadding$iv = 10; int rightPadding$iv = 10; int topPadding$iv = $this$updatePadding$iv.getPaddingTop(); int bottomPadding$iv = $this$updatePadding$iv.getPaddingBottom(); $this$updatePadding$iv.setPadding( leftPadding$iv, topPadding$iv, rightPadding$iv, bottomPadding$iv);
42. val viewModel = ViewModelProviders.of(this).get(SpeakersViewModel::class.java) 42 inline fun <reified T : ViewModel> FragmentActivity.getViewModel(): T = ViewModelProviders.of(this).get(T::class.java) val viewModel = this.getViewModel<SpeakersViewModel>()
43. val viewModel = ViewModelProviders.of(this).get(SpeakersViewModel::class.java) 43 inline fun <reified T : ViewModel> FragmentActivity.getViewModel(): T = ViewModelProviders.of(this).get(T::class.java)
44. 44 inline fun <reified T : ViewModel> FragmentActivity.getViewModel(): T = ViewModelProviders.of(this).get(T::class.java) SpeakersViewModel val viewModel = ViewModelProviders.of(this).get(SpeakersViewModel::class.java)
45. 45 inline fun <reified T : ViewModel> FragmentActivity.getViewModel(): T = ViewModelProviders.of(this).get(T::class.java) val viewModel = getViewModel<SpeakersViewModel>()
46. 46 val viewModel = getViewM
47. 47 viewGroup.isEmpty() viewGroup.isNotEmpty() viewGroup.childCount != 0
48. 48 menu.contains(menuItem) for(index in 0 until menu.size()) { if(menu.getItem(index) == menuItem) { return true } return false }
49. 49 sessionTitle.handler.postDelayed({}, 300)
50. 50 inline fun Handler.postDelayed(delay: Long, crossinline block: () -> Unit) { postDelayed({ block() }, delay) } sessionTitle.handler.postDelayed({}, 300)
51. 51 inline fun Handler.postDelayed(delay: Long, crossinline block: () -> Unit) { postDelayed({ block() }, delay) } sessionTitle.handler.postDelayed(300) { //does something }
52. val color = Color.rgb(255, 64, 129) 52 val red = Color.red(color) val green = Color.green(color) val blue = Color.blue(color) val invColor = Color.rgb(255 - red, 255 - green, 255 - blue)
53. val color = Color.rgb(255, 64, 129) 53 val red, = Color.red(color) val green, = Color.green(color) val blue, = Color.blue(color) val invColor = Color.rgb(255 - red, 255 - green, 255 - blue)
54. val color = Color.rgb(255, 64, 129) 54 val red, = color.red val green, = color.green val blue, = color.blue val invColor = Color.rgb(255 - red, 255 - green, 255 - blue)
55. 55 val red, = color.red val green, = color.green val blue, = color.blue inline val @receiver:ColorInt Int.red: Int get() = Color.red(this) inline val @receiver:ColorInt Int.green: Int get() = Color.green(this) inline val @receiver:ColorInt Int.blue: Int get() = Color.blue(this)
56. val color = Color.rgb(255, 64, 129) 56 val red, = color.red val green, = color.green val blue, = color.blue val invColor = Color.rgb(255 - red, 255 - green, 255 - blue)
57. val color = Color.rgb(255, 64, 129) 57 val red, = color.red val green, = color.green val blue, = color.blue val invColor = Color.rgb(255 - red, 255 - green, 255 - blue)
58. val color = Color.rgb(255, 64, 129) 58 val (red, green, blue) = color val invColor = Color.rgb(255 - red, 255 - green, 255 - blue)
59. 59 data class Color( val red: Int, val green: Int, val blue: Int )
60. val color = Color.rgb(255, 64, 129) 60 val (red, green, blue) = color val invColor = Color.rgb(255 - red, 255 - green, 255 - blue)
61. 61 val (red, green, blue) = color inline operator fun @receiver:ColorInt Int.component1(): Int = this.red inline operator fun @receiver:ColorInt Int.component2(): Int = this.green inline operator fun @receiver:ColorInt Int.component3(): Int = this.blue
62. speakerInputField.addTextChangedListener(object : TextWatcher { override fun afterTextChanged(speakerName: Editable?) { adapter.filterByName(speakerName.toString()) } override fun beforeTextChanged(s: CharSequence?, start: Int, count: Int, after: Int) { //does nothing } override fun onTextChanged(s: CharSequence?, start: Int, before: Int, count: Int) { //does nothing } }) speakerInputField.addTextChangedListener(object : TextWatcher { override fun afterTextChanged(speakerName: Editable?) { adapter.filterByName(speakerName.toString()) } override fun beforeTextChanged(s: CharSequence?, start: Int, count: Int, after: Int) { //does nothing } override fun onTextChanged(s: CharSequence?, start: Int, before: Int, count: Int) { //does nothing } }) 62
63. 63 speakerInputField.addTextChangedListener(object : TextWatcher { override fun afterTextChanged(speakerName: Editable?) { adapter.filterByName(speakerName.toString()) } … })
64. fun EditText.afterTextChanged(block:(String) -> Unit) { addTextChangeListener(object : TextWatcher { override fun afterTextChanged(text: Editable?) { block(text.toString()) } override fun beforeTextChanged(s: CharSequence?, start: Int, count: Int, after: Int) {} override fun onTextChanged(s: CharSequence?, start: Int, before: Int, count: Int) {} }) } speakerInputField.addTextChangedListener(object : TextWatcher { override fun afterTextChanged(speakerName: Editable?) { adapter.filterByName(speakerName.toString()) } … }) speakerInputField.addTextChangedListener(object : TextWatcher { override fun afterTextChanged(speakerName: Editable?) { adapter.filterByName(speakerName.toString()) } … }) 64
65. fun EditText.afterTextChanged(block:(String) -> Unit) { addTextChangeListener(object : TextWatcher { override fun afterTextChanged(text: Editable?) { block(text.toString()) } override fun beforeTextChanged(s: CharSequence?, start: Int, count: Int, after: Int) {} override fun onTextChanged(s: CharSequence?, start: Int, before: Int, count: Int) {} }) } fun EditText.afterTextChanged(block:(String) -> Unit) { addTextChangeListener(object : TextWatcher { override fun afterTextChanged(text: Editable?) { block(text.toString()) } override fun beforeTextChanged(s: CharSequence?, start: Int, count: Int, after: Int) {} override fun onTextChanged(s: CharSequence?, start: Int, before: Int, count: Int) {} }) } speakerInputField.addTextChangedListener(object : TextWatcher { override fun afterTextChanged(speakerName: Editable?) { adapter.filterByName(speakerName.toString()) } … }) speakerInputField.addTextChangedListener(object : TextWatcher { override fun afterTextChanged(speakerName: Editable?) { adapter.filterByName(speakerName.toString()) } … }) 65
66. fun EditText.afterTextChanged(block:(String) -> Unit) { addTextChangeListener(object : TextWatcher { override fun afterTextChanged(text: Editable?) { block(text.toString()) } override fun beforeTextChanged(s: CharSequence?, start: Int, count: Int, after: Int) {} override fun onTextChanged(s: CharSequence?, start: Int, before: Int, count: Int) {} }) } fun EditText.afterTextChanged(block:(String) -> Unit) { addTextChangeListener(object : TextWatcher { override fun afterTextChanged(text: Editable?) { block(text.toString()) } override fun beforeTextChanged(s: CharSequence?, start: Int, count: Int, after: Int) {} override fun onTextChanged(s: CharSequence?, start: Int, before: Int, count: Int) {} }) } 66 speakerInputField.afterTextChanged { speakerName -> adapter.filterByName(speakerName) }
67. 67 speakerInputField.afterTextChanged { speakerName -> adapter.filterByName(speakerName) } speakerInputField.beforeTextChanged { } speakerInputField.onTextChanged { } speakerInputField.addTextChangeListeners( afterTextChanged = { … }, onTextChanged = { … } )
68. 68 fun EditText.addTextListeners( afterTextChanged: (String) -> Unit = {}, beforeTextChanged: (CharSequence?, Int, Int) -> Unit = {_,_,_ -> }, onTextChanged: (CharSequence?, Int, Int, Int) -> Unit = {_,_,_,_ -> }, ) { addTextChangeListener(object : TextWatcher { override fun afterTextChanged(text: Editable?) { afterTextChanged(text.toString() } override fun beforeTextChanged(s: CharSequence?, start: Int, count: Int, after: Int) { beforeTextChanged(s, start, count) } override fun onTextChanged(s: CharSequence?, start: Int, before: Int, count: Int) { onTextChanged(s, start, before, count) } }) }
69. 69 animator.addListener(object : Animator.AnimatorListener { override fun onAnimationRepeat(animation: Animator?) { } override fun onAnimationEnd(animation: Animator?) { } override fun onAnimationCancel(animation: Animator?) { } override fun onAnimationStart(animation: Animator?) { } })
70. 70 animator.addListener(object : Animator.AnimatorListener { override fun onAnimationRepeat(animation: Animator?) { } override fun onAnimationEnd(animation: Animator?) { } override fun onAnimationCancel(animation: Animator?) { } override fun onAnimationStart(animation: Animator?) { } }) animator.doOnRepeat { } animator.doOnEnd { } animator.doOnCancel { } animator.doOnStart { } animator.addListener(doOnEnd = { }, doOnCancel = { })
71. 71 class SpeakersAdapter : RecyclerView.Adapter<SpeakersAdapter.ViewHolder>() { private val speakerList: MutableList<Speaker> = mutableListOf() override fun onCreateViewHolder(parent: ViewGroup, vt: Int): ViewHolder {...} override fun onBindViewHolder(vHolder: ViewHolder, position: Int) {...} override fun getItemCount(): Int {...} fun addAllSpeakers(speakers: List<Speaker>) { speakerList.clear() speakerList.addAll(speakers) notifyDataSetChanged() } }
72. 72 class SpeakersAdapter : RecyclerView.Adapter<SpeakersAdapter.ViewHolder>() { private val speakerList: MutableList<Speaker> = mutableListOf() override fun onCreateViewHolder(parent: ViewGroup, vt: Int): ViewHolder {...} override fun onBindViewHolder(vHolder: ViewHolder, position: Int) {...} override fun getItemCount(): Int {...} fun addAllSpeakers(speakers: List<Speaker>) { speakerList.clear() speakerList.addAll(speakers) notifyDataSetChanged() } } class SpeakersAdapter : RecyclerView.Adapter<SpeakersAdapter.ViewHolder>() { private val speakerList: MutableList<Speaker> = mutableListOf() override fun onCreateViewHolder(parent: ViewGroup, vt: Int): ViewHolder {...} override fun onBindViewHolder(vHolder: ViewHolder, position: Int) {...} override fun getItemCount(): Int {...} fun addAllSpeakers(speakers: List<Speaker>) { speakerList.clear() speakerList.addAll(speakers) notifyDataSetChanged() } }
73. 73 class SpeakersAdapter : RecyclerView.Adapter<SpeakersAdapter.ViewHolder>() { … fun addAllSpeakers(speakers: List<Speaker>) { speakerList.clear() speakerList.addAll(speakers) notifyDataSetChanged() } }
74. 74 class SpeakersAdapter : RecyclerView.Adapter<SpeakersAdapter.ViewHolder>() { … fun addAllSpeakers(speakers: List<Speaker>) { speakerList.clear() speakerList.addAll(speakers) notifyDataSetChanged() } } inline fun RecyclerView.Adapter.notifyDataSetChangedAfter(action:() -> Unit){ action() notifyDataSetChanged() }
75. 75 class SpeakersAdapter : RecyclerView.Adapter<SpeakersAdapter.ViewHolder>() { … fun addAllSpeakers(speakers: List<Speaker>) { speakerList.clear() speakerList.addAll(speakers) notifyDataSetChanged() } } inline fun RecyclerView.Adapter.notifyDataSetChangedAfter(action:() -> Unit){ action() notifyDataSetChanged() } inline fun RecyclerView.Adapter.notifyDataSetChangedAfter(action:() -> Unit){ action() notifyDataSetChanged() } class SpeakersAdapter : RecyclerView.Adapter<SpeakersAdapter.ViewHolder>() { … fun addAllSpeakers(speakers: List<Speaker>) { speakerList.clear() speakerList.addAll(speakers) notifyDataSetChanged() } }
76. 76 inline fun RecyclerView.Adapter.notifyDataSetChangedAfter(action:() -> Unit){ action() notifyDataSetChanged() } inline fun RecyclerView.Adapter.notifyDataSetChangedAfter(action:() -> Unit){ action() notifyDataSetChanged() } class SpeakersAdapter : RecyclerView.Adapter<SpeakersAdapter.ViewHolder>() { … fun addAllSpeakers(speakers: List<Speaker>) = notifyDataSetChangedAfter { speakerList.clear() speakerList.addAll(speakers) } }
77. 77 inline fun RecyclerView.Adapter.notifyDataSetChangedAfter(action:() -> Unit){ action() notifyDataSetChanged() } fun addAllSpeakers(speakers: List<Speaker>) = notifyDataSetChangedAfter { speakerList.clear() speakerList.addAll(speakers) } inline fun RecyclerView.Adapter.notifyDataSetChangedAfter(action:() -> Unit){ action() notifyDataSetChanged() }
78. Guidelines 78
79. Make sure you are adding value to your code 79 Guidelines
80. 80 inline fun View.onClick(crossinline block: (View) -> Unit) { setOnClickListener { block(this} } } searchIcon.setOnClickListener { //do something }
81. 81 inline fun View.onClick(crossinline block: (View) -> Unit) { setOnClickListener { block(this} } } searchIcon.onClick { //do something }
82. Make sure you are adding value to your code 82 Guidelines
83. 83 •make sure you are adding value to your code Guidelines
84. Prefer readability over conciseness 84 Guidelines
85. 85 •make sure you are adding value to your code •prefer readability over conciseness Guidelines
86. 86 •make sure you are adding value to your code •prefer readability over conciseness Guidelines
87. Be careful with optimizations 87 Guidelines
88. 88 •make sure you are adding value to your code •prefer readability over conciseness •be careful with optimizations Guidelines
89. Leverage features unique to Kotlin 89
90. Use extension functions and properties to alias robust API 90 Leverage features unique to Kotlin
91. Leverage features unique to Kotlin 91 •use extension functions and properties to alias robust API
92. Leverage features unique to Kotlin 92 •use extension functions and properties to alias robust API •use inline modifier
93. Use inline modifier 93 Unless it causes an increase in code size and allocation
94. Leverage features unique to Kotlin 94 •use extension functions and properties to alias robust API •use inline modifier
95. Leverage features unique to Kotlin 95 •use extension functions and properties to alias robust API •use inline modifier •use reified types
96. Leverage features unique to Kotlin 96 •use extension functions and properties to alias robust API •use inline modifier •use reified types •use object destructuring
98. Questions?.Answers!! 98
99. Thank you and have a nice Kotlin! @TheTechW0lf 99