java - Kotlin JNA 将声明的字段名称设为空列表

Question

下面的代码深受 this answer 的启发。和 this answer ，我试图让它与 Kotlin 语言一起工作，而不是在那里的答案中给出的 Java。

它基本上基于 JNA(Java Native Access)，它本质上是拉取 SYSTEM_BATTERY_STATE从 Windows native 库(在 C++ 上)获取有关笔记本电脑电池的信息。

该代码在 Java 版本中按预期工作，但如果我尝试对 Kotlin 做同样的事情，我会收到一个异常，说声明的字段名称是一个空列表/数组。

fun main() { getBatteryState() }

fun getBatteryState(): SYSTEM_BATTERY_STATE? {
    val batteryState = SYSTEM_BATTERY_STATE()
    val retrieveValue = PowrProf.CallNtPowerInformation(
        5,
        Pointer.NULL,
        0,
        batteryState,
        batteryState.size().toLong()
    )

    return if (retrieveValue == 0) batteryState else null
}

interface PowrProf : StdCallLibrary {
    @Suppress("FunctionName")
    fun CallNtPowerInformation(informationLevel: Int, inBuffer: Pointer?, inBufferLen: Long, outBuffer: SYSTEM_BATTERY_STATE?, outBufferLen: Long): Int

    companion object : PowrProf by Native.load("PowrProf", PowrProf::class.java)!!
}

class SYSTEM_BATTERY_STATE : Structure(ALIGN_MSVC), Structure.ByReference {
    var AcOnLine: Byte = 0
    var BatteryPresent: Byte = 0
    var Charging: Byte = 0
    var Discharging: Byte = 0

    var Spare1_0: Byte = 0
    var Spare1_1: Byte = 0
    var Spare1_2: Byte = 0
    var Spare1_3: Byte = 0

    var MaxCapacity = 0
    var RemainingCapacity = 0
    var Rate = 0

    var EstimatedTime = 0
    var DefaultAlert1 = 0
    var DefaultAlert2 = 0

    override fun getFieldOrder(): List<String> {
        return listOf(
            "AcOnLine", "BatteryPresent", "Charging", "Discharging",
            "Spare1_0", "Spare1_1", "Spare1_2", "Spare1_3",
            "MaxCapacity", "RemainingCapacity", "Rate",
            "EstimatedTime", "DefaultAlert1", "DefaultAlert2"
        )
    }
}

Exception in thread "main" java.lang.Error: Structure.getFieldOrder() on class com.animeshz.github.batteryinfo.SYSTEM_BATTERY_STATE returns names ([AcOnLine, BatteryPresent, Charging, DefaultAlert1, DefaultAlert2, Discharging, EstimatedTime, MaxCapacity, Rate, RemainingCapacity, Spare1_0, Spare1_1, Spare1_2, Spare1_3]) which do not match declared field names ([])
    at com.sun.jna.Structure.getFields(Structure.java:1089)
    at com.sun.jna.Structure.deriveLayout(Structure.java:1232)
    at com.sun.jna.Structure.calculateSize(Structure.java:1159)
    at com.sun.jna.Structure.calculateSize(Structure.java:1111)
    at com.sun.jna.Structure.allocateMemory(Structure.java:414)
    at com.sun.jna.Structure.<init>(Structure.java:205)
    at com.sun.jna.Structure.<init>(Structure.java:193)
    at com.sun.jna.Structure.<init>(Structure.java:180)
    at com.animeshz.github.batteryinfo.SYSTEM_BATTERY_STATE.<init>(SYSTEM_BATTERY_STATE.kt:9)
    at com.animeshz.github.batteryinfo.UtilKt.getBatteryState(util.kt:11)
    at com.animeshz.github.batteryinfo.UtilKt.main(util.kt:60)
    at com.animeshz.github.batteryinfo.UtilKt.main(util.kt)

为什么声明的字段名称是空数组/列表？我该如何解决这个问题？

Answer 1

JNA Structure类使用反射来查找字段名称，这意味着它们必须声明为 public字段/属性。 @JvmField annotation in Kotlin删除 getter 并根据需要公开这些属性。我怀疑这应该对你有用(未经测试):

class SYSTEM_BATTERY_STATE( 
        @JvmField var AcOnLine: Byte = 0,
        @JvmField var BatteryPresent: Byte = 0,
        @JvmField var Charging: Byte = 0,
        @JvmField var Discharging: Byte = 0,

        @JvmField var Spare1_0: Byte = 0,
        @JvmField var Spare1_1: Byte = 0,
        @JvmField var Spare1_2: Byte = 0,
        @JvmField var Spare1_3: Byte = 0,

        @JvmField var MaxCapacity = 0,
        @JvmField var RemainingCapacity = 0,
        @JvmField var Rate = 0,

        @JvmField var EstimatedTime = 0,
        @JvmField var DefaultAlert1 = 0,
        @JvmField var DefaultAlert2 = 0
    ) : Structure(ALIGN_MSVC), Structure.ByReference {

    override fun getFieldOrder() = listOf(
            "AcOnLine", "BatteryPresent", "Charging", "Discharging",
            "Spare1_0", "Spare1_1", "Spare1_2", "Spare1_3",
            "MaxCapacity", "RemainingCapacity", "Rate",
            "EstimatedTime", "DefaultAlert1", "DefaultAlert2"
        )
}