Google I/O 2018’s Extensions🦔

Kotlin大好き！Kotlin愛好会 vol4で発表しました．
是非Googleさんを参考にしましょう！

Transcript

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9. // Listͱ͔ͰView͕ΨλϯͬͯͳͬͨΓ͢ΔͷΛ๷͙༻ɽ
   inline fun T.executeAfter(block: T.() ->Unit){
   block()
   // ͙͢ʹbinding͍ͤͨ࣌͞ʹ࢖͏ɽ
   executePendingBindings()
   }
   // ࢖༻ྫ
   binding.executeAfter {
   //͜͜Ͱbind͢Δɽ
   event = item
   }
   ᶃ
   

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10. // TransitionΛ஗Ԇͤ͞Δ
    fun Activity.postponeEnterTransition(timeout: Long) {
    postponeEnterTransition()
    window.decorView.postDelayed(timeout) {
    startPostponedEnterTransition()
    }
    }
    // ࢖༻ྫ
    activity?.postponeEnterTransition(500L)
    ᶄ
    

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11. // ॳظԽɼࢀর͕ৗʹγϯάϧεϨουͰ͔͠ߦΘΕͳ͍࣌༻ɽ
    fun lazyFast(operation: () -> T): Lazy =
    lazy(LazyThreadSafetyMode.NONE) {
    operation()
    }
    // SYNCRONIZED: σϑΥϧτɽ୯ҰεϨου͔ΒͷॳظԽͰɼෳ਺εϨου͔Βͷࢀর͕Մೳɽ
    // PUBLICATION: ෳ਺εϨου͔ΒॳظԽ͠Α͏ͱ͢Δࣄ͕Մೳɽ
    // ࢖༻ྫ
    private val day: Int by lazyFast {
    val args = arguments ?: throw
    IllegalStateException("Missing arguments!")
    args.getInt(ARG_INT)
    }
    ᶅ
    

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12. inline fun
    FragmentActivity.viewModelProvider(
    provider: ViewModelProvider.Factory
    ) =
    ViewModelProviders.of(this, provider).get(VM::class.java)
    // ࢖༻ྫ
    // Before
    val viewModel: HogeViewModel =
    ViewModelProviders.of(this, viewModelFactory)
    .get(HogeViewModel::class.java)
    //After
    val viewModel: HogeViewModel =
    viewModelProvider(viewModelFactory)
    ᶆ
    

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13. fun ViewGroup.inflate(
    @LayoutRes layout: Int, attachToRoot: Boolean = false
    ): View {
    return LayoutInflater.from(context)
    .inflate(layout, this, attachToRoot)
    }
    // ࢖༻ྫ
    …
    Holder(
    parent.inflate(VIEW_TYPE_HEADING, false)
    )
    ᶇ
    

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14. inline fun FragmentManager.inTransaction(
    func: FragmentTransaction.() -> FragmentTransaction
    ) {
    beginTransaction().func().commit()
    }
    // ࢖༻ྫ
    supportFragmentManager.inTransaction {
    add(FRAGMENT_ID, fragment)
    }
    ᶈ
    

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15. // enumΫϥεΛbundleʹೖΕΕΔܗʹ͢Δ
    fun > Bundle.putEnum(key: String, value: T) =
    putString(key, value.name)
    // ↑ͰೖΕͨenumΫϥεΛऔΓग़͢
    inline fun > Bundle.getEnum(key: String):
    T = enumValueOf(getString(key))
    // ParcelʹbooleanΛॻ͖ࠐΉ
    fun Parcel.writeBoolean(value: Boolean) = writeInt(if (value)
    1 else 0)
    // ↑Ͱม׵ͨ͠booleanΛಡΈࠐΉ
    fun Parcel.readBoolean() = readInt() != 0
    ᶉ
    

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16. // ࢖༻ྫ
    // ಡΈ΍͍͢ʂ
    pacel.apply {
    writeInt(state)
    writeInt(peekHeight)
    writeBoolean(isFitToContents)
    writeBoolean(isHideable)
    writeBoolean(skipCollapsed)
    writeBoolean(isDraggable)
    }
    

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17. fun MutableLiveData.setValueIfNew(newValue: T) {
    if (this.value != newValue) value = newValue
    }
    fun MutableLiveData.postValueIfNew(newValue: T) {
    if (this.value != newValue) postValue(newValue)
    }
    // ObserverଆͰ൑ఆͨ͠ํ͕҆શͳؾ͕͢Δ͚ͲͲ͏ͳΜͩΖ͏ɽɽ
    ᶊ
    

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18. fun LiveData.map(body: (X) -> Y): LiveData {
    return Transformations.map(this, body)
    }
    fun LiveData.switchMap(body: (X) -> LiveData):
    LiveData {
    return Transformations.switchMap(this, body)
    }
    ᶋ
    

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19. // ࢖༻ྫ
    liveData = parentLiveData.map {
    (it as? Result.Success)?.data?: 0
    }
    liveData = parentLiveData.switchMap {
    if(value == null) dataLiveData else parentLiveData
    }
    // ࠷ॳ֦ுؔ਺ͬͯࣄʹؾ͔ͮͣɼڻ͍ͨɽ
    

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20. val T.checkAllMatched: T
    get() = this
    // ࢖༻ྫ
    // OK
    when (sealed) {
    ONE -> {…}
    TWO -> {…}
    }.checkAllMatch
    // error
    when (sealed) {
    ONE -> {…}
    //TWO -> {…}
    }.checkAllMatch
    ᶌ
    

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22. 5IBOLZPV
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