如何将lateinit Kotlin属性设置为null

Question

下面的类有一个非常独特的生命周期,这需要我暂时清空lateinit属性

class SalesController : BaseController, SalesView {
    @Inject lateinit var viewBinder: SalesController.ViewBinder
    @Inject lateinit var renderer: SalesRenderer
    @Inject lateinit var presenter: SalesPresenter
    lateinit private var component: SalesScreenComponent

    override var state = SalesScreen.State.INITIAL  //only property that I want to survive config changes

    fun onCreateView(): View {  /** lateinit variables are set here */ }
    fun onDestroyView() {
         //lateinit variables need to be dereferences here, or we have a memory leak 
         renderer = null!! //here's the problem: throws exception bc it's a non-nullable property

}}

以下是框架使用它的方式.

controller.onCreateView() //same instance of controller
controller.onDestroyView() //same instance of controller
controller.onCreateView() //same instance of controller
controller.onDestroyView() //same instance of controller

我的lateinit属性被匕首注入,我需要将它们设置为null中onDestroyView-或有内存泄漏.然而,就我所知(没有反思)而言,这在kotlin中是不可能的.我可以使这些属性可以为空,但这会破坏Kotlin无效安全的目的.

我不太清楚如何解决这个问题.理想情况下,可能会有某种类型的注释处理器生成java代码以自动清空特定变量onDestroyView？

Answer 1

Kotlin lateinit属性null用作未初始化的标志值,并且没有干净的方法null在lateinit没有反射的属性的支持字段中设置.

但是,Kotlin允许您使用委托属性覆盖属性行为.似乎没有允许它的委托kotlin-stdlib,但如果你需要这个行为,你可以实现自己的委托来做到这一点,为你的utils添加一些代码:

class ResettableManager {
    private val delegates = mutableListOf<ResettableNotNullDelegate<*, *>>()

    fun register(delegate: ResettableNotNullDelegate<*, *>) { delegates.add(delegate) }

    fun reset() { delegatesToReset.forEach { it.reset() } }
}

class Resettable<R, T : Any>(manager: ResettableManager) {
    init { manager.register(this) }

    private var value: T? = null

    operator fun getValue(thisRef: R, property: KProperty<*>): T =
            value ?: throw UninitializedPropertyAccessException()

    operator fun setValue(thisRef: R, property: KProperty<*>, t: T) { value = t }

    fun reset() { value = null }
}

用法:

class SalesController : BaseController, SalesView {
    val resettableManager = ResettableManager()
    @set:Inject var viewBinder: SalesController.ViewBinder by Resettable(resettableManager)
    @set:Inject var renderer: SalesRenderer by Resettable(resettableManager)
    @set:Inject var presenter: SalesPresenter by Resettable(resettableManager)

    fun onDestroyView() {
        resettableManager.reset()
    }
}