Advanced Kotlin for Android #DroidKaigi #DroidKaigiB

DroidKaigi( https://droidkaigi.github.io/2016/ )で発表したスライドです。

Transcript

1. Advanced Kotlin for Android DroidKaigi Feb. 19, 2016 Taro @ngsw_taro
2. • 長澤太郎 - Taro Nagasawa • Twitter: @ngsw_taro • Programmer at M3, Inc. • Kotlin evangelist (unofficial) • Japan Kotlin User Group About me
3. エムスリー株式会社 - M3, Inc. • provide services for health care workers
4. Agenda • What is Kotlin • How to use Kotlin in Android projects • Real world Android Kotlin • Aggressive Kotlin • Summary
5. Agenda • What is Kotlin • How to use Kotlin in Android projects • Real world Android Kotlin • Aggressive Kotlin • Summary interest you in Kotlin
6. Agenda • What is Kotlin • How to use Kotlin in Android projects • Real world Android Kotlin • Aggressive Kotlin • Summary show tips and ideas
7. What is Kotlin
8. Kotlin • target JVM, JavaScript, Android • developed by JetBrains • Statically typed • Object-oriented • Modern grammar & features • The so-called “Better Java”
9. Like this package sample fun main(args: Array<String>) { "world".hello() } fun String.hello() { println("Hello, $this") }
10. Like this package sample fun main(args: Array<String>) { "world".hello() } fun String.hello() { println("Hello, $this") } top level function
11. Like this package sample fun main(args: Array<String>) { "world".hello() } fun String.hello() { println("Hello, $this") } extension function
12. Very easy data class User(val id: String, val name: String) fun loadUser(id: String) { apiClient.getUser(id) .observeOn(AndroidSchedulers.main()) .subscribe { user -> userNameView.text = user.name } }
13. Very easy data class User(val id: String, val name: String) fun loadUser(id: String) { apiClient.getUser(id) .observeOn(AndroidSchedulers.main()) .subscribe { user -> userNameView.text = user.name } } data class
14. Very easy data class User(val id: String, val name: String) fun loadUser(id: String) { apiClient.getUser(id) .observeOn(AndroidSchedulers.main()) .subscribe { user -> userNameView.text = user.name } } function literal
15. Very easy data class User(val id: String, val name: String) fun loadUser(id: String) { apiClient.getUser(id) .observeOn(AndroidSchedulers.main()) .subscribe { user -> userNameView.text = user.name } } property access
16. Very easy data class User(val id: String, val name: String) fun loadUser(id: String) { apiClient.getUser(id) .observeOn(AndroidSchedulers.main()) .subscribe { user -> userNameView.text = user.name } } like properties
17. The time has come!!! • 1.0 was released only a few days ago • Some companies started to use Kotlin • I am writing a Kotlin book now ◦ It will be released by this late summer
18. How to use Kotlin in Android projects
19. (1) start Kotlin in Android Projects
20. Kotlin plugin installation 1. launch Android Studio 2. open “Preferences” 3. click “Install JetBrains plugin…” 4. find “Kotlin” from the list, and click “Install plugin” 5. wait for installation to complete 6. restart AS to enable the plugin
21. convert MainActivity.java to Kotlin code Code menu
22. add config for Kotlin to build.gradle Tools menu
23. add config for Kotlin to build.gradle apply plugin: 'com.android.application' apply plugin: 'kotlin-android'
24. Finish • rename a directory “java” to “kotlin” • options ◦ specify Kotlin version in gradle.properties ◦ make project root depend on Kotlin plugin
25. (2) use Realm and Dagger
26. JSR269 Annotation processing • for generating “Java” code by annotations in compilation time • Useful libraries ◦ Dagger ◦ Realm ◦ Butter Knife ◦ etc...
27. kapt dependencies { // Realm compile "io.realm:realm-android:$version" kapt "io.realm:realm-android:$version" } kapt { generateStubs = true }
28. RealmObject open class User( open var id: Long = 0, @Required open var name: String = "" ): RealmObject()
29. RealmObject open class User( open var id: Long = 0, @Required open var name: String = "" ): RealmObject() provide setter/getter provide default constructor provide default constructor
30. Real world Android Kotlin
31. (1) Extensions
32. Extension function package sample fun main(args: Array<String>) { "world".hello() } fun String.hello() { println("Hello, $this") }
33. (Example) Toast fun Context.toast(message: String, duration: Int = Toast.LENGTH_SHORT) { Toast.makeText(this, message, duration).show() } // in Activity toast("Hello")
34. (Example) Application object val Activity.app: MyApp get() = application as MyApp // in Activity app.component.inject(this)
35. Scope functions provided by the stdlib cf. Kotlin スコープ関数 用途まとめ goo.gl/Ec1Gpi name receiver parameters return let T block: (T)->R R run T block: T.()->R R apply T block: T.()->Unit T with - receiver: T, block: T.()->R R * T and R are any types.
36. (Example) execute Intent startActivity(createIntent(this) .addFlags(Intent.FLAG_ACTIVITY_NEW_TASK) .addFlags(Intent.FLAG_ACTIVITY_CLEAR_TASK) .putExtra("key", "value")) createIntent(this) .addFlags(Intent.FLAG_ACTIVITY_NEW_TASK) .addFlags(Intent.FLAG_ACTIVITY_CLEAR_TASK) .putExtra("key", "value") .let { startActivity(it) }
37. (Example) No longer need fluent interface createIntent(this).run { addFlags(Intent.FLAG_ACTIVITY_NEW_TASK) addFlags(Intent.FLAG_ACTIVITY_CLEAR_TASK) if(value != null) { putExtra("key", value) } startActivity(this) }
38. (Example) new a fragment with arguments class MyFragment: Fragment() { companion object { fun new(foo: Int, bar: Int): MyFragment = MyFragment().apply { arguments = Bundle().apply { putInt("foo", foo) putInt("bar", bar) } } } }
39. (2) Delegated properties
40. delegate other objects to property access class Greeter { val message: String by lazy { "Hello" } } lazy init
41. (Example) Extra fun Activity.stringExtra(name: String): Lazy<String> = lazy { requireNotNull(intent.getStringExtra(name), {"missing"}) } class MyActivity: Activity() { val message: String by stringExtra("message") override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) Log.d("MyActivity", message) } }
42. Kotter Knife • View binding library for Kotlin • developed by Jake Wharton • use delegated properties val submitButton: Button by bindView(R.id.submit) val nameTextView: TextView? by bindOptionalView(R.id.name)
43. (3) Nullable
44. Null-Safety • A mechanism to eliminate NullPointerException val s1: String = null // NG val s2: String? = null // OK s2.toUpperCase() // NG if(s2 != null) s2.toUppserCase() // OK s2?.toUpperCase() // OK
45. let is map, flatMap, ifPresent for the Optional in Java fun reverse(s: String): String {...} val reverse: String? = str?.let { reverse(it) } fun findById(id: Long): User? {...} val user: User? = userId?.let { findById(it) } user?.let { println(it }
46. let is useful, but if here are multiple nullable... foo?.let { foo -> bar?.let { bar -> baz?.let { baz -> execute(foo, bar, baz) } } } deep nesting ugly (´;ω;`)
47. Use if expression if (foo != null && bar != null && baz != null) { execute(foo, bar, baz) }
48. When foo, bar, baz are “var” properies... if (foo != null && bar != null && baz != null) { // NG because they are stil nullable execute(foo, bar, baz) } for { foo <- foo bar <- bar baz <- baz } yield execute(foo, bar, baz) Kotlin dose not have such syntax
49. Answer 1: early returns fun method() { val foo = foo ?: return val bar = bar ?: return val baz = baz ?: return execute(foo, bar, baz) }
50. Answer 2: early returns + “run” fun method() { run { val foo = foo ?: return@run val bar = bar ?: return@run val baz = baz ?: return@run execute(foo, bar, baz) } Log.d(TAG, "done!!!") }
51. Aggressive Kotlin
52. (1) Extensions in a interface
53. RxAndroid + RxLifecycle apiClient.findArticle(id) .compose(bindToLifecycle<Article>()) .observeOn(AndroidSchedulers.main()) .subscribe { articleView.article = it }
54. RxAndroid + RxLifecycle apiClient.findArticle(id) .compose(bindToLifecycle<Article>()) .observeOn(AndroidSchedulers.main()) .subscribe { articleView.article = it } cannot be inferred
55. A extension function is needed apiClient.findArticle(id) .bindToLifecycle() .observeOn(AndroidSchedulers.main()) .subscribe { articleView.article = it }
56. want to use a ActivityLifecycleProvider’s method, but how ? // BOF fun <T> Observable<T>.bindToLifecycle() = compose<T>(???) // EOF ActivityLifecycleProvider# bindToLifecycle
57. define a extension function in a interface // BOF interface RxLifecyclerFeature: ActivityLifecycleProvider { fun <T> Observable<T>.bindToLifecycle() = compose<T>(this@RxLifecyclerFeature.bindToLifecycle()) } // EOF
58. implemtns the interface class MyActivity: RxActivity(), RxLifecycleFeature { fun go() { apiClient.findArticle(id) .bindToLifecycle() .observeOn(AndroidSchedulers.main()) .subscribe { ... } } ...
59. (2) Extensions in a interface which has abstract methods
60. Can such a function be defined? createIntent(this) .addFlags(Intent.FLAG_ACTIVITY_NEW_TASK) .putExtra("key", "value") .startActivity()
61. Can this function be defined? createIntent(this) .addFlags(Intent.FLAG_ACTIVITY_NEW_TASK) .putExtra("key", "value") .startActivity() Intent’s method AND use Activity’s method (i.e. startActivity)
62. define a extension function in a interface // BOF interface IntentFeature { fun Intent.startActivity() { ??? } } // EOF
63. Additionally, define a abstract method // BOF interface IntentFeature { fun startActivity(intent: Intent) fun Intent.startActivity() { startActivity(this) } } // EOF
64. implement the interface class MyActivity: Activity(), IntentFeature { fun go() { createIntent(this) .addFlags(Intent.FLAG_ACTIVITY_NEW_TASK) .putExtra("key", "value") .startActivity() } ...
65. (3) “Double context extensions”
66. Without interfaces version class MyActivity: Activity() { fun go() { createIntent(this) .addFlags(Intent.FLAG_ACTIVITY_NEW_TASK) .putExtra("key", "value") .startActivity() } ...
67. provide a extension property // BOF val Activity.startActivity: Intent.()->Unit get() = { intent -> startActivity(intent) } // EOF
68. provide a extension property // BOF val Activity.startActivity: Intent.()->Unit get() = { intent -> startActivity(intent) } // EOF Activity’s property
69. provide a extension property // BOF val Activity.startActivity: Intent.()->Unit get() = { intent -> startActivity(intent) } // EOF Intent’s method Intent’s method
70. Usage class MyActivity: Activity() { fun go() { createIntent(this) .addFlags(Intent.FLAG_ACTIVITY_NEW_TASK) .putExtra("key", "value") .startActivity() } ...
71. Usage class MyActivity: Activity() { fun go() { createIntent(this) .addFlags(Intent.FLAG_ACTIVITY_NEW_TASK) .putExtra("key", "value") .startActivity() } ... Activity’s property, which returns a Intent’method
72. Usage class MyActivity: Activity() { fun go() { createIntent(this) .addFlags(Intent.FLAG_ACTIVITY_NEW_TASK) .putExtra("key", "value") .startActivity() } ... Method invocation Method invocation
73. I named this pattern “double context extension” • Pros ◦ expressive ◦ keep your code base simple • Cons ◦ Code completion dose not work
74. Summary
75. Summary • Kotlin is a pragmatic language for Android • The time has come! • Getting started is easy • Extensions & scope functions are your friends • It’s easy to deal with nullable • Interfaces make extensions more powerful • “Double context extensions”, my idea
76. Thank you, Enjoy Kotlin