Kotlin 靜態初始化中的 ExceptionInInitializerError

Question

我有一個 Kotlin 類，通過一個伴隨對象進行了一些靜態初始化。 但是當我嘗試運行我的應用程序時，我收到了一個 ExceptionInInitializerError 錯誤。

這是堆棧跟蹤：

 Caused by: java.lang.ExceptionInInitializerError
    at com.myapp.model.location.CountryList.getSelectableCountryList(CountryList.kt:19)
    at com.myapp.ui.util.CountryStateSpinnerSet.<init>(CountryStateSpinnerSet.java:43)
    at java.lang.reflect.Constructor.newInstance0(Native Method) 
    at java.lang.reflect.Constructor.newInstance(Constructor.java:343) 
    .
    .
    .
 Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.Object java.util.HashMap.get(java.lang.Object)' on a null object reference
    at com.myapp.model.location.Country.<init>(Country.kt:31)
    at com.myapp.model.location.Country.<init>(Country.kt:17)
    at com.myapp.model.location.Country.<clinit>(Country.kt:19)
    at com.myapp.model.location.CountryList.getSelectableCountryList(CountryList.kt:19) 
    at com.myapp.ui.util.CountryStateSpinnerSet.<init>(CountryStateSpinnerSet.java:43) 
    at java.lang.reflect.Constructor.newInstance0(Native Method) 
    at java.lang.reflect.Constructor.newInstance(Constructor.java:343) 
    .
    .
    .

還有我的兩個班級：

國家列表：

object CountryList {
  val countryList: List<Country>
    get() {
        return listOf(
                Country.UNITED_STATES, Country.CANADA
        )
    }

  @JvmStatic val selectableCountryList: List<Country>
    get() {
        val countryList: MutableList<Country> = mutableListOf(Country.SELECT) <-- the ExceptionInInitializerError occurs on this line
        countryList.addAll(countryList)

        return countryList
    }
}

國家：

data class Country(val name: String, val abbrev: String = ""): Parcelable {
  companion object {
    val SELECT = Country("Select Country")

    val UNITED_STATES = Country("United States", "US")
    val CANADA = Country("Canada", "CA")

    private var countryStateMap: HashMap<Country, StateList> = hashMapOf(
        UNITED_STATES to USStateList(),
        CANADA to CanadaProvinceList()
    )
  }

@IgnoredOnParcel
val stateList: StateList = countryStateMap[this]!!

@IgnoredOnParcel
val selectableStateList: List<State>
    get() = if (null != countryStateMap[this]) {
        countryStateMap[this]!!.selectableStateList
    }
    else {
        throw IllegalStateException("Can't retrieve selectable state list with country: $this")
    }

override fun toString(): String {
    val sb = StringBuilder()
    if (abbrev.isNotEmpty()) {
        sb.append(abbrev)
        sb.append(" - ")
    }
    sb.append(name)
    return sb.toString()
}
}

我是否以錯誤的順序初始化某些東西？

先感謝您。

Answer 1

我假設 Country.SELECT 在訪問時尚未初始化。 嘗試通過添加by lazy來更改初始化順序，這會告訴 kotlin 稍后初始化 CountryList。

object CountryList {
  val countryList: List<Country> by lazy {
     ...

CountryList 將在第一次實際使用時進行初始化。 屆時 Country.SELECT 可用。