Question

从类定义开始，如下所示：

class Player {
    var playbackFile: AudioFileID? = nil
    var packetPosition: Int64 = 0
    var numPacketsToRead: UInt32 = 0
    var packetDescs: UnsafeMutablePointer<AudioStreamPacketDescription>? = nil
    var isDone = false
}

然后定义一个回调函数：

let AQOutputCallback: AudioQueueOutputCallback = {(inUserData, inAQ, inCompleteAQBuffer) -> () in
   let aqp = UnsafeMutablePointer<Player>(inUserData).pointee // this gives an error

// more code
}

这导致第二行出错：“无法使用类型为'UnsafeMutableRawPointer？'的参数列表调用类型'UnsafeMutablePointer'的初始值设定项？

如何从“UnsafeMutableRawPointer”类型中正确转换？ Swift 3中的'UnsafeMutablePointer'？

Answer 1

以下修改消除了错误：

let aqp = inUserData!.assumingMemoryBound(to: Player.self).pointee

Answer 2

将MutableRawPointer转换为object，我们使用fromOpaque api

/// Unsafely turns an opaque C pointer into an unmanaged class reference.
///
/// This operation does not change reference counts.
///
///     let str: CFString = Unmanaged.fromOpaque(ptr).takeUnretainedValue()
///
/// - Parameter value: An opaque C pointer.
/// - Returns: An unmanaged class reference to `value`.
public static func fromOpaque(_ value: UnsafeRawPointer) -> Unmanaged<Instance>

示例：

var info:UnsafeMutableRawPointer = ....
let obj = Unmanaged<$AnyObject>.fromOpaque(info).takeUnretainedValue()

将“UnsafeMutableRawPointer”类型的变量强制转换为UnsafeMutablePointer＆lt;＆gt;在Swift 3中

2 个答案: