Kotlin-Multiplatform 中的 CPointer

Question

我找不到任何关于如何在 Kotlin Multiplatform 中获取 CPointer 的示例，现有的文档也没有多大帮助。在我的 iOS 源集中，我需要构建与以下 Swift 代码等效的 Kotlin（仅包括代码的相关部分）：

  ...(hex: String) {

if hex.hasPrefix("#") {
    let start = hex.index(hex.startIndex, offsetBy: 1)
         let scanner = Scanner(string: hexColor)
         var hexNumber: UInt64 = 0



          if scanner.scanHexInt64(&hexNumber) {

            r = CGFloat((hexNumber & 0xff000000) >> 24) / 255
           ....

我遇到问题的具体部分是

scanner.scanHexInt64(&hexNumber)

这是 Kotlin 代码和问题

//input to function - hex: String
    val scanner = NSScanner(hex)
    if (hex.startsWith("#")) {
        scanner.scanLocation = 1u
    }
    var hexNumber : UInt32 = 0u
    /*Type mismatch.
    Required:
    CPointer<UIntVar /* = UIntVarOf<UInt> */>?
    Found:
    UInt32 /* = UInt */
     */
    //HOW TO GET CPOINTER TO hexNumber?
    scanner.scanHexInt(hexNumber)

根据文档：（link)

Pointers and arrays are mapped to CPointer<T>?.

但是如何呢？

Answer 1

找到了我的问题的答案。必须使用

memScoped

。

memScoped {
        var pointed : UIntVar = alloc<UIntVar>()
        scanner.scanHexInt(pointed.ptr)
        val alpha: CGFloat = 1.0
        val pointedValue = pointed.value
        val r: CGFloat = (((pointedValue and 0xFF0000) shr 16)/255.0)
        ....
}

互联网上关于此的唯一来源（关于应用它来获取指针）在这里 - link

memScoped

inline fun <R> memScoped(block: MemScope.() -> R): R
Runs given block providing allocation of memory which will be automatically disposed at the end of this scope

其中，使用扩展函数alloc()得到CVariable

fun <reified T : CVariable> NativePlacement.alloc(): T

然后您可以通过另一个扩展函数访问指针

val <T : CPointed> T.ptr: CPointer<T>

回想起来一切都非常清楚，并且清楚原来以错误的方式解决了问题，希望通过类似CPointer<UInt> = ...的方式获得指针 https://kotlinlang.org/docs/reference/native/c_interop.html

的官方文档

Answer 2

import kotlinx.cinterop.UIntVar
import kotlinx.cinterop.memScoped
import kotlinx.cinterop.ptr
import platform.CoreGraphics.CGFloat
import platform.Foundation.NSScanner
import platform.Foundation.scanHexInt
import platform.UIKit.UIColor
import kotlinx.cinterop.alloc
import kotlinx.cinterop.value

fun hexToUIColor(hexStr: String): UIColor {
    var cString: String = hexStr.toUpperCase()

    if (cString.startsWith("#")) {
        cString = cString.removePrefix("#")
    }

    if (cString.length != 8) {
        return UIColor.grayColor
    }

    var a: UInt
    var r: UInt
    var g: UInt
    var b: UInt

    memScoped {
        val scanner = NSScanner(cString)
        var pointed : UIntVar = alloc<UIntVar>()
        scanner.scanHexInt(pointed.ptr)
        val alpha: CGFloat = 1.0
        val pointedValue: UInt = pointed.value

        a = ((pointedValue and 4278190080u) shl 24) / 255u
        r = ((pointedValue and 16711680u) shl 16) / 255u
        g = ((pointedValue and 65280u) shl 8) / 255u
        b = ((pointedValue and 255u) shl 0) / 255u

        return UIColor(red = r.toDouble(), green = g.toDouble(), blue = b.toDouble(), alpha = a.toDouble())
    }
}

Kotlin-Multiplatform 中的 CPointer

CPointer in Kotlin-Multiplatform

c

kotlin

swift

kotlin-native

kotlin-multiplatform