Dont worry - switch to Kotlin

Transcript

1. Kotlin
2. Why … ? - “To invent the wheel” - Marketing - Сuriosity - “I do not like”
3. Android 1.0 (Apple Pie) - 2008 year - java 6
4. Android 6.0 - 2015 year - java 6* *with pieces of java 7
5. Android 7.0 JAVA 8
6. Lambdas
7. Java 6/7 and
8. What's wrong with java?
9. Create class Person ID + First name + Last name +
10. Create class person
15. Statically typed programming language for the JVM. Android and the browser 100% interoperable with Java
17. What is the difference between Kotlin and Java?
18. KOTLIN CAT JAVA CAT
20. Why do we need Kotlin? • Stuck on java 6 (7) ◦ No streams ◦ No try-with-resources ◦ No lambdas, methods refs -> Use RxJava -> Use Retrolambda -> minSdkVersion = 19 or Retrolambda • Java language problems ◦ “Util Hell” ◦ Nullability problems ◦ Mutability problems ◦ General verbosity of common idioms
21. Syntax Crash Course
22. Syntax Crash Course
23. Syntax Crash Course
24. Syntax Crash Course
25. Kotlin Features String templates Properties Lambdas Inline functions Data class Smart cast Null safety Default values for function parameters Lazy property Extension Functions Equals Single-expression functions When expression let, apply, use, with Collections Kotlin Android Extensions Plugin Anko
26. String templates
27. String templates >
28. Properties
29. Properties
30. Extension Functions What it does ? How?
31. Extension Functions fun showToast(context: Context, @StringRes idRes: Int){ Toast.makeText(context, idRes, Toast.LENGTH_LONG).show() } class MainActivity: AppCompatActivity() { fun showInfo() { showToast(this, R.string.error_network) } }
32. Extension Functions
33. Extension Functions fun Context.showToast(@StringRes idRes: Int){ Toast.makeText(this, idRes, Toast.LENGTH_LONG).show() } class MainActivity: AppCompatActivity() { fun showInfo() { // or this.showToast(R.string.error_network) showToast(R.string.error_network) } }
34. Extension Functions fun Float.dpToPx(): Int { val metrics = Resources.getSystem().displayMetrics val px = this * (metrics.densityDpi / 160f) return Math.round(px) } fun Int.pxToDp(): Int { val metrics = Resources.getSystem().displayMetrics val dp = this / (metrics.densityDpi / 160f) return Math.round(dp) }
35. Lambdas Function that is not declared, but passed immediately as an expression.
36. Lambdas
37. Lambdas
38. Lambdas
39. Lambdas
40. Lambdas
41. Lambdas Expensive operation
42. Lambdas invoke lambda
43. Lambdas invoke lambda
44. Lambdas and Closures
45. Inline functions
46. Creating a new lambda reference
47. Inline functions
48. Data class What it does ? Nothing. Just hold data What it provides ? - getters, setters - equals() / hashCode() - toString - copy() function
49. Data class > Person(id=1, firstName=Bogdan, lastName=Salo)
50. Smart cast
51. Smart cast
52. Smart cast
53. Smart cast smart cast
54. Null safety Kotlin’s type system is aimed to eliminate NullPointerException’s from our code.
55. Null safety
56. Null safety compilation error
57. Null safety
58. Null safety compilation error
59. Null safety
60. Null safety
61. Null safety
62. Null safety
63. Null safety
64. Null safety
65. Default values for function parameters Function parameters can have default values, which are used when a corresponding argument is omitted. This allows for a reduced number of overloads compared to other languages.
66. Default values for function parameters
67. Default values for function parameters
68. Default values for function parameters
69. Default values for function parameters
70. Lazy property Value gets computed only upon first access.
71. Lazy property val preference = getSharedPreferences("pref") override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) val username = preference.getString("username") } crash, require context
72. Lazy property val preference = getSharedPreferences("pref") override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) val username = preference.getString("username") }
73. Lazy property val preference by lazy { getSharedPreferences("pref") } override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) val username = preference.getString("username") }
74. Lazy property val validator: Validator by lazy { Validator(this) } button1.click { validator.validate() } button2.click { validator.validate()}
75. Single-expression functions
76. Single-expression functions
77. Single-expression functions return type is optional
78. Single-expression functions
79. When expression
80. When expression
81. When expression can be anything
82. When expression can be anything
83. When expression
84. When expression
85. When expression
86. When expression
87. let, apply, use, with Higher-order functions - function that takes functions as parameters, or returns a function.
88. let (scope function)
89. let Preferences.getUser().let { showUserName(it.name) showUserEmail(it.email) }
90. let supportActionBar?.let { it.setTitle(R.string.basket) it.setDisplayShowTitleEnabled(true) it.setHomeButtonEnabled(true) it.setDisplayHomeAsUpEnabled(true) }
91. with
92. with recyclerView.setHasFixedSize(true) recyclerView.addItemDecoration(createDecorator()) recyclerView.layoutManager = LinearLayoutManager(context) recyclerView.adapter = myAdapter
93. with with (recyclerView) { recyclerView.setHasFixedSize(true) recyclerView.addItemDecoration(createDecorator()) recyclerView.layoutManager = LinearLayoutManager(context) recyclerView.adapter = myAdapter }
94. with with (recyclerView) { recyclerView.setHasFixedSize(true) recyclerView.addItemDecoration(createDecorator()) recyclerView.layoutManager = LinearLayoutManager(context) recyclerView.adapter = myAdapter } not need
95. with with (recyclerView) { setHasFixedSize(true) addItemDecoration(createDecorator()) layoutManager = LinearLayoutManager(context) adapter = myAdapter }
96. with with (recyclerView) { setHasFixedSize(true) addItemDecoration(createDecorator()) layoutManager = LinearLayoutManager(context) adapter = myAdapter }
97. with inline fun <T: BaseInteractor> withInteractor(receiver: T, block: T.() -> Unit) = receiver.block() withInteractor(loginInteractor) { loginCustomer(password, username) .execute({ onLoginSuccess(it) }, { ErrorHandler.onError(router, it) }) }
98. apply
99. apply SomeModel() .apply { isHeader = true } .apply { nameHeader = "I`m header" }
100. use (try with resources function)
101. use (try with resources function) fun countUsers(): Long { val database = openDatabase() val result = database.count("users") database.close() return result } need to close
102. use (try with resources function) fun countUsers(): Long { val database = openDatabase() val result = database.count("users") database.close() return result } fun countUsers() = openDatabase().use { it.count("users") } need to close
103. use (try with resources function) fun countUsers(): Long { val database = openDatabase() val result = database.count("users") database.close() return result } fun countUsers() = openDatabase().use { it.count("users") } automatically close database
104. Collections
105. Collections no such method
106. Collections > [1, null, 2, null, 3, 4, 5, 6, 7, 8, 9]
107. Collections > [1, 2, 3, 4, 5, 6, 7, 8, 9]
108. Collections > [2, 4, 6, 8]
109. Collections > [8, 6, 4, 2]
110. Collections enum
111. Collections enum
112. Collections getOrElse() find() filter() filterNot() filterNotNull() flatMap() take() takeLast() sortBy() sumBy() sortByDescending() groupBy() map() mapNotNull() all() any() maxBy() minBy() minWith() zip() ….
113. findViewById()
114. Kotlin Android Extensions Plugin What it does ? How?
115. Kotlin Android Extensions Plugin buildscript { dependencies { classpath "org.jetbrains.kotlin:kotlin-android-extensions:$kotlin_version" } } apply plugin: 'kotlin-android-extensions'
116. Kotlin Android Extensions Plugin // R.layout.activity_order_info import kotlinx.android.synthetic.main.activity_order_info.*
117. Kotlin Android Extensions Plugin // R.layout.activity_order_info import kotlinx.android.synthetic.main.activity_order_info.* public class OrderInfoActivity: AppCompatActivity() { override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) setContentView(R.layout.activity_order_info) txtTitle.text = "Hello, Kotlin!" btnHello.setOnClickListener {...} } }
118. Kotlin Android Extensions Plugin // R.layout.activity_order_info import kotlinx.android.synthetic.main.activity_order_info.* public class OrderInfoActivity: AppCompatActivity() { override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) setContentView(R.layout.activity_order_info) txtTitle.text = "Hello, Kotlin!" btnHello.setOnClickListener {...} } } <Button android:id="@+id/btnHello" android:layout_width="match_parent" android:layout_height="wrap_content"/>
119. Anko What it does ?
120. Intents
121. Intents
122. Some useful intents
123. Services
124. Services
125. Async
126. Async
127. Compatibility with Java - 100% - Kotlin can call any method from Java - Java can call any function from Kotlin - Add Kotlin to an existing Java project is very simple
128. Thank you for attention!