SavedStateHandleDelegate.kt

class SavedStateHandleDelegate<T>(
    private val savedStateHandle: SavedStateHandle,
    private val key: String,
    defaultValue: T,
    initializer: (valueLoadedFromState: T?, setter: (T) -> Unit) -> Unit
) : ReadWriteProperty<Any, T> {
    private val state: MutableState<T>

    init {
        val savedValue = savedStateHandle.get<T>(key)
        state = mutableStateOf(
            savedValue ?: defaultValue
        )
        initializer(savedValue, ::updateValue)
    }

    override fun getValue(thisRef: Any, property: KProperty<*>) = state.value

    override fun setValue(thisRef: Any, property: KProperty<*>, value: T) {
        updateValue(value)
    }

    private fun updateValue(value: T) {
        state.value = value
        savedStateHandle.set(key, value)
    }
}