为什么我得到信息 Enum argument can be null in Java, but exhaustive when contains no null branch in Kotlin？

Question

代码B运行正常，但是代码A出现如下警告提示（可以运行），为什么？

枚举参数在 Java 中可以为 null，但在不包含 null 分支时是详尽无遗的

我认为_playState.value在代码B中也可以为空，我在代码B中使用exhaustive when时是否应该添加空分支？

代码A

private val _selectAction = MutableLiveData<ESelect>()
val selectAction: LiveData<ESelect> = _selectAction

selectAction.observe(mLifecycleOwner) {
   when(it) {               //Enum argument can be null in Java, but exhaustive when contains no null branch                                   
         ESelect.SelectAll    -> binding.chSelect.isChecked = true
         ESelect.UnselectAll  -> binding.chSelect.isChecked = false
         ESelect.NoAction     -> Unit
   }
}



enum class ESelect{
    SelectAll,
    UnselectAll,
    NoAction  
}

代码B

private val _playState=MutableLiveData<EPlayState>()

 override fun playOrPause(filename: String) {
        when (_playState.value) {
           EPlayState.STOPPED -> play(filename)
           EPlayState.PLAYING -> pause()
           EPlayState.PAUSED  -> resume()
        }
    }


enum class EPlayState {
    STOPPED,
    PLAYING,
    PAUSED
}

Answer 1

LiveData写成Java。传递给 observe() 函数的第二个参数是 Java 接口 Observer 的匿名实现。由于 Java 对 Kotlin 中的可空性一无所知，因此假定参数 it 可以为空。

为什么我得到信息 Enum argument can be null in Java, but exhaustive when contains no null branch in Kotlin？

Why do I get the information Enum argument can be null in Java, but exhaustive when contains no null branch in Kotlin?

kotlin

android-livedata