Property delegate useful for Android development. Allows to declare lazily evaluated properties dependant on Activity Context and avoid memory leaks.

LifecycleAwareLazy.kt

class LifecycleAwareLazy<T>(lifecycle: Lifecycle, private val initializer: () -> T) :
        Lazy<T>, GenericLifecycleObserver {

    init {
        lifecycle.addObserver(this)
    }

    private object UNINITIALIZED_VALUE

    private var _value: Any? = UNINITIALIZED_VALUE

    @get:Synchronized
    override val value: T
        get() {
            if (_value === UNINITIALIZED_VALUE) {
                _value = initializer.invoke()
            }
            return _value as T
        }

    override fun isInitialized(): Boolean = _value != UNINITIALIZED_VALUE

    // GenericLifecycleObserver
    override fun onStateChanged(source: LifecycleOwner?,
                                event: Lifecycle.Event?) =
            when (event) {
                Lifecycle.Event.ON_STOP -> {
                    _value = UNINITIALIZED_VALUE
                }
                else -> Unit
            }
}