かゆいところに手が届くKotlin

Kotlin's 8 tips.

Transcript

1. ͔Ώ͍ͱ͜Ζʹ
   ख͕ಧ͘ ,PUMJO
   /JHIU
   
   !NBUUBL
2. ,PUMJOͷศརͳॻ͖ํ
   ͭ঺հ͢ΔΑ
3. MB[Z
   ✨ΪϦΪϦ·Ͱ࣮ߦ͠ͳ͍✨
4. class Person( val firstName: String, val lastName: String ) { val fullName by lazy { “${firstName}, ${lastName}” } } // ͜ͷ࣌఺Ͱ͸ fullName͸ͭ͘ΒΕͳ͍ val person = Person(“John”, “Due”) // ΞΫηεͯ͠ॳΊͯ࡞੒͞ΕΔ println(person.fullName)
5. 
   
   MFU
   
   OJM
   DPBMFTDJOH
   PQFSBUPS
   ✨JGMFUͯ͠ฦΓ஋͕΄͍͠✨
6. // ී௨ͷॻ͖ํ var name: String? = “Kana” var message: String = if (name!=null) “Hello, ${name}!” else “Hello.” // let+null coalescing op var name: String? = “Kana” var message: String = name?.let { “Hello, ${it}!” } ?: “Hello.”
7. 
   
   DMBTTKBWB ✨KBWBͷΫϥεΦϒδΣΫτ͕΄͍͠✨
8. // ී௨ͷॻ͖ํ javaClass<Sample>() // M13Ҏ߱ͷॻ͖ํ Sample::class.java // ࢖͍υίϩɺ(TPOύʔε͢Δͱ͖ͳͲ val gson = Gson() val person = gson.fromJson(“{\”name\”: \”Ocelot\”}”, Person::class.java)
9. 
   
   HFUUFSTFUUFS
   ✨HFUUFSTFUUFS͕͔ΜͨΜʹ͔͚ΔΑ✨
10. // Computed properties class Duration(val interval: Long) { var seconds: Double get() = interval.toDouble() / 1000 set(value) { this.interval = value * 1000 } } // javaͷsetter/getter͕KotlinͩͱpropertyʹͳΔΑ person.name = “John” // person.setName(String name) person.name // person.getName()
11. 
    
    0CKFDU
    ✨4JOHMFUPO͕΄͍͠ʂ✨
12. // java class Singleton { private static Singleton instance = null; public static Singleton getInstance() { if (instance == null) { instance = new Singleton(); } return instance; } } // kotlin object Singleton() // Object͸lazy. ॳճΞΫηεͰOFX͞ΕΔ Singleton
13. // java class NotSingleton { public static void callClassMethod() {} } NotSingleton.callClassMethod(); // kotlin class NotSingleton { companion object { fun callClassMethod() {} } } NotSingleton.callClassMethod()
14. 
    
    UIJT!
    ✨ͲͷUIJT͔໌ࣔͯ͠ΞΫηε͍ͨ͠✨
15. class A { inner class B { fun doit() { val a = this@A // instance of class A val b = this@B // instance of class B } } }
16. 
    
    6OJU
    ✨+BWBͷ7PJEʹରԠ͢Δ΍ͭ✨
17. public open class UpdateModel { // ΠϕϯτΛૹ৴͍͚ͨ͠Ͳɺແҙຯͳ஋ΛૹΓ͍ͨ࣌ͱ͔ val updateEvent by lazy { BehaviorSubject.create<Unit>() } fun update() { // Unit͸ Object. ৽͍͠instanceΛͭ͘Βͳ͍ updateEvent.onNext(Unit) } }
18. 
    
    &YUFOTJPO
    ✨طଘͷΫϥεʹϝιουΛ෇͚଍͍ͨ͠✨
19. // طଘͷΫϥεΛ֦ுग़དྷΔ fun <T> Observable<T?>.notNulls(): Observable<T> { return this.filter { it != null }. map { it!! } } // ΑΓγϯϓϧʹʂ val observable = Observable.just<Int?>(1, null, 2, null) val normal = observable.filter { it != null }. map { it !! } val pretty = observable.notNulls()
20. ͍͡ΐ͏Ͱ͢
    ✨&OKPZ
    LPUMJO✨