Succumb to the Kotlin side

Introduction talk to Kotlin for Android developers.

Transcript

1. Succumb to the Kotlin side
2. Who am I?
3. Acknowledge
4. Index
5. Constructors class Person {}
6. Constructors class Person constructor(firstName: String) {}
7. Constructors class Person(firstName: String) {} (if no annotations or visibility modifiers)
8. Constructors class Person(firstName: String) { init { //We can use/initialize firstName here } }
9. Constructors class Person(val firstName: String) {}
10. Constructors class Person(val firstName: String = "Alberto") {}
11. Constructors data class Person(val firstName: String = "Alberto"){}
12. Constructors data class Person(val firstName: String = "Alberto"){} • equals()/hashCode() • toString() of the form "Person(firstName=Alberto)" • componentN() functions • copy()
13. Constructors data class Person(val firstName: String = "Alberto"){} // val alberto = Person() val joe = Person("Joe")
14. Constructors data class Person(val firstName: String = "Alberto"){} // val alberto = Person() val joe = Person("Joe") Ok, but...
15. Constructors data class Person(val firstName: String = "Alberto"){} // val alberto = Person() val joe = Person("Joe") Where´s the “new”?
16. Constructors data class Person(val firstName: String = "Alberto"){} // val alberto = Person() val joe = Person("Joe") Where´s the “new”? and the semicolon!?
17. Functions fun read(items: Array<Int>, offset: Int = 0, length: Int = items.size()) { // ... }
18. Functions fun read(items: Array<Int>, offset: Int = 0, length: Int = items.size()) { // ... } read(ArrayOf(1, 2, 3))
19. Functions fun read(items: Array<Int>, offset: Int = 0, length: Int = items.size()) { // ... } read(ArrayOf(1, 2, 3), length = 1)
20. Control flow (I) var max: Int if (a > b) //do some stuff max = a else //do some stuff max = b
21. Control flow (I) var max: Int if (a > b) //do some stuff max = a else //do some stuff max = b (but… if is now an expression)
22. Control flow (I) var max = if (a > b) //do some stuff a else //do some stuff b (if branches can be blocks, and the last expression is the value of a block)
23. Control flow (I) var max = if (a > b) a else b (and for simpler ifs...)
24. Control flow (I) var max = if (a > b) a else b
25. Control flow (II) switch (x) { 1 -> print("x is 1") 2 -> print("x is 2") }
26. Control flow (II) switch (x) { 1 -> print("x is 1") 2 -> print("x is 2") }
27. Control flow (II) when (x) { 1 -> print("x is 1") 2 -> print("x is 2") }
28. Control flow (II) when (x) { 0, 1 -> print("x is 0 or 1") 2 -> print("x is 2") }
29. Control flow (II) when (x) { in 1..10 -> print("x is in the range") in validNumbers -> print("x is valid") !in 10..20 -> print("x is outside the range") else -> print("none of the above") } (validNumbers is a collection)
30. Control flow (II) val hasPrefix = when(x) { is String -> x.startsWith("prefix") else -> false } (since here when is an expression we’re forced to put the else)
31. Control flow (II) val hasPrefix = when(x) { is String -> x.startsWith("prefix") else -> false } (since here when is an expression we’re forced to put the else)
32. Control flow (extra) if (obj is String) { // At this point obj is magically a String! print(obj.length) }
33. Null safety var a: String = "abc" a = null a.capitalize()
34. Null safety var a: String = "abc" a = null a.capitalize() Kotlin Quiz a) NullPointerException
35. Null safety var a: String = "abc" a = null a.capitalize() Kotlin Quiz a) NullPointerException b) Compilation error
36. Null safety var a: String = "abc" a = null a.capitalize() Kotlin Quiz a) NullPointerException b) Compilation error c) Nothing, the method won´t be executed
37. Null safety var a: String = "abc" a = null a.capitalize() Kotlin Quiz a) NullPointerException b) Compilation error c) Nothing, the method won´t be executed d) Assertion error
38. Null safety var a: String = "abc" a = null a.capitalize() Kotlin Quiz a) NullPointerException b) Compilation error c) Nothing, the method won´t be executed d) Assertion error e) I really think it´s a NullPointerException
39. Null safety var a: String = "abc" a = null // compilation error a.capitalize()
40. Null safety var a: String? = "abc" a = null a.capitalize()
41. Null safety var a: String? = "abc" a = null a.capitalize() // compilation error
42. Null safety var a: String? = "abc" a = null if (a != null) { a.capitalize() }
43. Null safety var a: String? = "abc" a = null if (a != null) { // boring a.capitalize() }
44. Null safety var a: String? = "abc" a = null if (a != null) { // boring a.capitalize() } // 3 lines
45. Null safety var a: String? = "abc" a = null if (a != null) { // boring a.capitalize()// 17 characters for a null-check } // 3 lines
46. Null safety var a: String? = "abc" a = null a?.capitalize()
47. Null safety var a: String? = "abc" a = null a ?.capitalize()
48. Null safety var a: String? = "abc" a = null a ?.capitalize() // 1 char
49. Null safety var a: String? = "abc" a = null a ?.capitalize() // 1 char, 16 less than before :)
50. Null safety var a: String? = "abc" var b = if (a != null) { a.capitalize() } else { "" }
51. Null safety var a: String? = "abc" var b = a?.capitalize() else ""
52. Null safety var a: String? = "abc" var b = a?.capitalize() else ""
53. Null safety var a: String? = "abc" var b = a?.capitalize() ?: ""
54. Null safety var a: String? = "abc" var b = a?.capitalize() ?: ""
55. Static
56. Static Doesn’t exist
57. Static Doesn’t exist Bye utils?
58. Static Doesn’t exist Bye singleton? Bye utils?
59. Object window.addMouseListener(object : MouseAdapter() { override fun mouseClicked(e: MouseEvent) { // ... } } // This is an Object expression
60. Object object StuffManager { fun registerStuff(stuff: Stuff) { // ... } val allStuffs: Collection<Stuff> get() = // ... } // This is an Object declaration
61. Object object StuffManager { fun registerStuff(stuff: Stuff) { // ... } val allStuffs: Collection<Stuff> get() = // ... } // This is an Object declaration Hello singleton!
62. Object class MyClass { companion object { fun getSomeUtilStuff() { //... } } } Hello utils
63. Object class MyClass { companion object { fun getSomeUtilStuff() { //... } } } Hello utils?
64. Extension Functions // Java code public static void hideImage(ImageView image) { image.setVisibility(View.GONE); image.setImageResource(0); } UiUtils.hideImage(new ImageView(context));
65. Extension Functions // Kotlin magic fun ImageView.hide() { visibility = View.GONE setImageResource(0) }
66. Extension Functions // Kotlin magic fun ImageView.hide() { visibility = View.GONE setImageResource(0) } // import com.xing.core.extensions.hide ImageView(context).hide()
67. Higher-Order Functions fun <T> logException(func: () -> T): T? { try { return func() } catch (ignored: Throwable) { Log.e("ERROR", "...") return null } }
68. Higher-Order Functions fun <T> logException(func: () -> T) = try { return func() } catch (ignored: Throwable) { Log.e("ERROR", "...") return null }
69. Higher-Order Functions inline fun <T> logException(func: () -> T) = try { return func() } catch (ignored: Throwable) { Log.e("ERROR", "...") return null }
70. Higher-Order Functions inline fun <T> logException(func: () -> T) = try { return func() } catch (ignored: Throwable) { Log.e("ERROR", "...") return null } // ... logException({ myDangerousMethod() })
71. Higher-Order Functions inline fun <T> logException(func: () -> T) = try { return func() } catch (ignored: Throwable) { Log.e("ERROR", "...") return null } // ... logException { myDangerousMethod() }
72. Extensions + High-Order = Awesomeness val prefs = context.getSharedPreferences(...) val edit = prefs.edit() edit.putBoolean("enabled", true) edit.commit()
73. Extensions + High-Order = Awesomeness val prefs = context.getSharedPreferences(...) // in some method... edit("enabled", true) fun edit(key: String, value: Boolean) { prefs.edit().putBoolean(key, value).commit() }
74. Extensions + High-Order = Awesomeness val prefs = context.getSharedPreferences(...) // in some method... edit("enabledCount", 1) fun edit(key: String, value: Boolean) { prefs.edit().putBoolean(key, value).commit() }
75. Extensions + High-Order = Awesomeness val prefs = context.getSharedPreferences(...) // in some method... edit("enabledCount", 1) fun edit(key: String, value: Boolean) { prefs.edit().putBoolean(key, value).commit() } fun edit(key: String, value: Int) { prefs.edit().putInt(key, value).commit() }
76. Extensions + High-Order = Awesomeness val prefs = context.getSharedPreferences(...) // in some method... edit("enabledCount", 1F) fun edit(key: String, value: Boolean) { prefs.edit().putBoolean(key, value).commit() } fun edit(key: String, value: Int) { prefs.edit().putInt(key, value).commit() }
77. Extensions + High-Order = Awesomeness val prefs = context.getSharedPreferences(...) // in some method... edit("enabledCount", 1F) fun edit(key: String, value: Boolean) { prefs.edit().putBoolean(key, value).commit() } fun edit(key: String, value: Int) { prefs.edit().putInt(key, value).commit() } fun edit(key: String, value: Float) { prefs.edit().putFloat(key, value).commit() }
78. Extensions + High-Order = Awesomeness val prefs = context.getSharedPreferences(...) // in some method... edit("enabledCount", 1L) fun edit(key: String, value: Boolean) { prefs.edit().putBoolean(key, value).commit() } fun edit(key: String, value: Int) { prefs.edit().putInt(key, value).commit() } fun edit(key: String, value: Float) { prefs.edit().putFloat(key, value).commit() }
79. Extensions + High-Order = Awesomeness inline fun SharedPreferences.inEdit( func: () -> Unit) { val editor = edit() func() editor.commit() }
80. Extensions + High-Order = Awesomeness inline fun SharedPreferences.inEdit( func: () -> Unit) { val editor = edit() func() editor.commit() } prefs.inEdit { prefs.putBoolean(...) }
81. Extensions + High-Order = Awesomeness inline fun SharedPreferences.inEdit( func: () -> Unit) { val editor = edit() func() editor.commit() } prefs.inEdit { prefs.putBoolean(...) }
82. Extensions + High-Order = Awesomeness inline fun SharedPreferences.inEdit( func: (SharedPreferences.Editor) -> Unit) { val editor = edit() func() editor.commit() } prefs.inEdit { prefs.putBoolean(...) }
83. Extensions + High-Order = Awesomeness inline fun SharedPreferences.inEdit( func: (SharedPreferences.Editor) -> Unit) { val editor = edit() func(editor) editor.commit() } prefs.inEdit { prefs.putBoolean(...) }
84. Extensions + High-Order = Awesomeness inline fun SharedPreferences.inEdit( func: (SharedPreferences.Editor) -> Unit) { val editor = edit() func(editor) editor.commit() } prefs.inEdit { editor -> editor.putBoolean(...) }
85. Extensions + High-Order = Awesomeness inline fun SharedPreferences.inEdit( func: (SharedPreferences.Editor) -> Unit) { val editor = edit() func(editor) editor.commit() } prefs.inEdit { it.putBoolean(...) }
86. Extensions + High-Order = Awesomeness inline fun SharedPreferences.inEdit( func: SharedPreferences.Editor.() -> Unit) { val editor = edit() func(editor) editor.commit() } prefs.inEdit { it.putBoolean(...) }
87. Extensions + High-Order = Awesomeness inline fun SharedPreferences.inEdit( func: SharedPreferences.Editor.() -> Unit) { val editor = edit() editor.func() editor.commit() } prefs.inEdit { it.putBoolean(...) }
88. Extensions + High-Order = Awesomeness inline fun SharedPreferences.inEdit( func: SharedPreferences.Editor.() -> Unit) { val editor = edit() editor.func() editor.commit() } prefs.inEdit { putBoolean(...) }
89. And more...
90. And more... Because… why not?
91. Android extensions import kotlinx.android.synthetic.main.activity_main.* class MyActivity : Activity() { override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) setContentView(R.layout.activity_main) // Instead of findView(R.id.textView) as TextView textView.text = "Hello, world!" } }
92. Examples (1) Bundle args = getArguments() if (args != null) { String data = args.getString(DATA_ARG) if (data != null) { data.getBytes() } }
93. Examples (1) Bundle args = getArguments() if (args != null) { String data = args.getString(DATA_ARG) if (data != null) { data.getBytes() } }
94. Examples (1) getArguments()?.getString(DATA_ARG)?.getBytes()
95. Examples (2) imm = getContext().getSystemService(Context.INPUT_METHOD_SERVICE) as InputMethodManager imm.hideSoftInputFromWindow(yourEditText.getWindowToken(), 0)
96. Examples (2) fun View.hideKeyboard() { imm = getContext().getSystemService( Context.INPUT_METHOD_SERVICE) as InputMethodManager imm.hideSoftInputFromWindow(getWindowToken(), 0) }
97. Examples (2) fun View.hideKeyboard() { imm = getContext().getSystemService( Context.INPUT_METHOD_SERVICE) as InputMethodManager imm.hideSoftInputFromWindow(getWindowToken(), 0) } yourEditText.hideKeyboard()
98. Examples (3) Bundle bigBundle = Bundle() bigBundle.putString(/**/) bigBundle.putInt(/**/) bigBundle.putString(/**/) bigBundle.putString(/**/)
99. Examples (3) Bundle bigBundle = Bundle() bigBundle.apply { putString(/**/) putInt(/**/) putString(/**/) putString(/**/) //… }
100. What can be optimized • Every Utils class • Duplicated boilerplate code ◦ Model classes ◦ Actions we do in single objects (Picasso) • Whenever you have to write the same word multiple times (almost)
101. Some cons (because nobody is perfect)
102. Some cons (because nobody is perfect)
103. Some cons (because nobody is perfect)
104. Some cons (because nobody is perfect)
105. Some cons (because nobody is perfect)
106. Some cons (because nobody is perfect)
107. Is it worth? Well, that's up to one person…
108. Is it worth? Well, that's up to one person…
109. Is it worth? Well, that's up to one person… (and your coworkers)
110. Is it worth? Well, that's up to one person… (and your coworkers) (and your tech lead)
111. Is it worth? Well, that's up to one person… (and your coworkers) (and your tech lead) (and you might want to tell your PO as well…)
112. Is it worth? Well, that's up to one person… (and your coworkers) (and your tech lead) (and you might want to tell your PO as well…) (yeah, better create a meeting for that)
113. Is it worth? Well, that's up to one person… (and your coworkers) (and your tech lead) (and you might want to tell your PO as well…) (yeah, better create a meeting for that) Silver Bullet principle
114. Links
115. Q&A