WIP: Delegate which will automatically handle onSaveInstanceState/onRestoreInstanceState of property

SavedStateDelegate.kt

package *

import android.util.*
import androidx.core.os.bundleOf
import androidx.savedstate.SavedStateRegistryOwner
import kotlin.properties.ReadWriteProperty
import kotlin.reflect.KProperty

inline fun <reified T : Any?> SavedStateRegistryOwner.savedState(initValue: T) =
    object : ReadWriteProperty<SavedStateRegistryOwner, T> {
        private var value: T = initValue
        private lateinit var key: String
        private lateinit var mainKey: String

        override fun setValue(thisRef: SavedStateRegistryOwner, property: KProperty<*>, value: T) {
            tryRegister(property.name)
            this.value = value
        }

        override fun getValue(thisRef: SavedStateRegistryOwner, property: KProperty<*>): T {
            tryRegister(property.name)
            value = savedStateRegistry.consumeRestoredStateForKey(mainKey)?.get(key) as? T ?: value
            return value
        }

        private fun tryRegister(propertyName: String) {
            if (::key.isInitialized) return

            key = "savedState.$propertyName"
            mainKey = this@savedState::class.java.name + "." + key
            savedStateRegistry.registerSavedStateProvider(mainKey) {
                bundleOf(key to value)
            }
        }
    }

inline fun <reified T : Any?> SavedStateRegistryOwner.savedState() = savedState<T?>(null)