利用Kotlin属性委托获取Activity传递的参数

ActivityKt.kt

import android.app.Activity
import android.content.Context
import android.content.Intent
import android.os.Bundle
import android.os.Parcelable
import kotlin.properties.ReadOnlyProperty
import kotlin.reflect.KProperty

class ActivityOptions {
    var flags: Int = 0

    fun flag(flag: Int) {
        flags = flags or flag
    }
}

class ExtrasBuilder {
    val bundle = Bundle()

    fun int(key: String, value: Int) = bundle.putInt(key, value)
    fun long(key: String, value: Long) = bundle.putLong(key, value)
    fun string(key: String, value: String) = bundle.putString(key, value)
    fun boolean(key: String, value: Boolean) = bundle.putBoolean(key, value)
    fun parcelable(key: String, value: Parcelable) = bundle.putParcelable(key, value)
}

inline fun <reified T : Activity> Context.startActivity(
    options: ActivityOptions.() -> Unit = {},
    extras: ExtrasBuilder.() -> Unit
) {
    val opts = ActivityOptions().apply(options)
    val bundle = ExtrasBuilder().apply(extras).bundle
    startActivity(
        Intent(this, T::class.java).apply {
            addFlags(opts.flags)
            putExtras(bundle)
        }
    )
}

inline fun <reified T : Any> Activity.optionalExtras(key: String, defaultValue: T) =
    OptionalIntentExtra(key, defaultValue)

class OptionalIntentExtra<T : Any>(
    private val key: String, private val defaultValue: T
) : ReadOnlyProperty<Activity, T> {

    override fun getValue(thisRef: Activity, property: KProperty<*>): T {
        return thisRef.intent.extras?.get(key) as? T ?: defaultValue
    }
}

inline fun <reified T : Any> Activity.requiredExtra(key: String) = RequiredIntentExtra<T>(key)

class RequiredIntentExtra<T : Any>(
    private val key: String
) : ReadOnlyProperty<Activity, T> {

    override fun getValue(thisRef: Activity, property: KProperty<*>): T {
        return thisRef.intent.extras?.get(key) as? T ?: error("Missing required intent extra: $key")
    }
}