Intent.putExtras()←これ

Intent.putExtras()←これ Yahoo! JAPAN　森洋之

in the Stone Age

val intent = Intent(this, MyActivity2::class.java) intent.putExtra("foo", "FOO") intent.putExtra("bar", 333) startActivity(intent)

・口伝でのみ伝えられる、必須パラメータ・パラメータの型は、ムラハチレベルの掟

・キモい

・手続き的で、あまり読みたくないコード

拡張関数

inline fun <reified T : Activity> Context.startActivity( noinline extras: (Intent.()
-> Unit)? = null) { val intent = Intent(this, T::class.java) extras?.let { intent.extras() } startActivity(intent) }

startActivity<MyActivity2>{ putExtra("foo", "FOO") putExtra("bar", 333) } ・だいぶ読みやすくなった

startActivity<MyActivity2>{ putExtra("foo", "FOO") putExtra("bar", 333) } ・相変わらず、村の掟ベースのActivity起動

Companion Object

companion object { const val EXTRA_FOO = "foo" const val
EXTRA_BAR = "bar" fun showFoo(context: Context, foo: String, bar: Int) { context.startActivity<MyActivity2> { putExtra(EXTRA_FOO, foo) putExtra(EXTRA_BAR, bar) } } }

MyActivity2.showFoo(this, "FOO", 333) ・型セーフ・Null安全・村の掟からの解放

EXTRA_BAR = "bar" const val EXTRA_HOGE = "foo" const val EXTRA_FUGA = "bar" fun showFoo(context: Context, foo: String, bar: Int) { context.startActivity<MyActivity2> { putExtra(EXTRA_FOO, foo) putExtra(EXTRA_BAR, bar) } } fun showHoge(context: Context, hoge: String, fuga: String) { context.startActivity<MyActivity2> { putExtra(EXTRA_HOGE, hoge) putExtra(EXTRA_FUGA, fuga) } } } 受け付けるパターンが増えると

EXTRA_BAR = "bar" const val EXTRA_HOGE = "foo" const val EXTRA_FUGA = "bar" fun showFoo(context: Context, foo: String, bar: Int) { context.startActivity<MyActivity2> { putExtra(EXTRA_FOO, foo) putExtra(EXTRA_BAR, bar) } } fun showHoge(context: Context, hoge: String, fuga: String) { context.startActivity<MyActivity2> { putExtra(EXTRA_HOGE, hoge) putExtra(EXTRA_FUGA, fuga) } } }

override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) setContentView(R.layout.activity_main2) when { intent.extras.containsKey(EXTRA_FOO)
&& intent.extras.containsKey(EXTRA_BAR) -> { // foo pattern } intent.extras.containsKey(EXTRA_HOGE) && intent.extras.containsKey(EXTRA_FUGA) -> { // hoge pattern } else -> throw IllegalArgumentException("staticメソッドから起動してね ") } }

Sealed Class

private sealed class Extras { data class Foo(val foo :
String, val bar : Int) : Extras(), Parcelable { companion object { @JvmField @Suppress("unused") val CREATOR: Parcelable.Creator<Foo> = object : Parcelable.Creator<Foo> { override fun createFromParcel(source: Parcel): Foo = Foo(source) override fun newArray(size: Int): Array<Foo?> = arrayOfNulls(size) } } protected constructor(parcelIn: Parcel) : this(parcelIn.readString(), parcelIn.readInt()) override fun writeToParcel(dest: Parcel?, flags: Int) { dest?.writeString(foo) dest?.writeInt(bar) } override fun describeContents(): Int = 0 } data class Hoge(val hoge : String, val fuga : String) : Extras(), Parcelable { companion object { @JvmField @Suppress("unused") val CREATOR: Parcelable.Creator<Hoge> = object : Parcelable.Creator<Hoge> { override fun createFromParcel(source: Parcel): Hoge = Hoge(source) override fun newArray(size: Int): Array<Hoge?> = arrayOfNulls(size) } } protected constructor(parcelIn: Parcel) : this(parcelIn.readString(), parcelIn.readString()) override fun writeToParcel(dest: Parcel?, flags: Int) { dest?.writeString(hoge) dest?.writeString(fuga) } override fun describeContents(): Int = 0 } }

private sealed class Extras { data class Foo(val foo :
String, val bar : Int) : Extras(), Parcelable { companion object { @JvmField @Suppress("unused") val CREATOR: Parcelable.Creator<Foo> = object : Parcelable.Creator<Foo> { override fun createFromParcel(source: Parcel): Foo = Foo(source) override fun newArray(size: Int): Array<Foo?> = arrayOfNulls(size) } } protected constructor(parcelIn: Parcel) : this(parcelIn.readString(), parcelIn.readInt()) override fun writeToParcel(dest: Parcel?, flags: Int) { dest?.writeString(foo) dest?.writeInt(bar) } override fun describeContents(): Int = 0 } data class Hoge(val hoge : String, val fuga : String) : Extras(), Parcelable { companion object { @JvmField @Suppress("unused") val CREATOR: Parcelable.Creator<Hoge> = object : Parcelable.Creator<Hoge> { override fun createFromParcel(source: Parcel): Hoge = Hoge(source) override fun newArray(size: Int): Array<Hoge?> = arrayOfNulls(size) } } protected constructor(parcelIn: Parcel) : this(parcelIn.readString(), parcelIn.readString()) override fun writeToParcel(dest: Parcel?, flags: Int) { dest?.writeString(hoge) dest?.writeString(fuga) } override fun describeContents(): Int = 0 } } 論外

Parcelize

private sealed class Extras { @Parcelize data class Foo(val foo
: String, val bar : Int) : Extras(), Parcelable @Parcelize data class Hoge(val hoge : String, val fuga : String) : Extras(), Parcelable } ・Kotlin Android Extensionsで、Parcelableは簡単に作れる・experimental注意

companion object { fun showFoo(context: Context, foo : String, bar
: Int) { context.startActivity<MyActivity2> { putExtra(EXTRAS_KEY, Extras.Foo(foo, bar)) } } fun showHoge(context: Context, hoge : String, fuga : String) { context.startActivity<MyActivity2> { putExtra(EXTRAS_KEY, Extras.Hoge(hoge, fuga)) } } }

override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) setContentView(R.layout.activity_main2) val extras =
intent.getParcelableExtra<Parcelable>(EXTRAS_KEY) ?: throw IllegalArgumentException("staticメソッドから起動してね ") when(extras) { is Extras.Foo -> { // foo pattern } is Extras.Hoge -> { // hoge pattern } } }

委譲Property

class ExtraParcelable : ReadOnlyProperty<Activity, Parcelable> { override fun getValue(thisRef: Activity,
property: KProperty<*>) : Parcelable { return thisRef.intent.getParcelableExtra(EXTRAS_KEY) ?: throw IllegalArgumentException("extra parameter ${property.name} is null") } }

private val extras by ExtraParcelable() override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState) setContentView(R.layout.activity_main2) when(extras) { is Extras.Foo -> { // foo pattern } is Extras.Hoge -> { // hoge pattern } } }

おまけ

改訂版が出ます・2ヶ月半で500ページ書き直します

Intent.putExtras()←これ

Intent.putExtras()←これ

kobito-kaba

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