Swift 2-UnsafeMutablePointer 反对

Question

如果我有类似的方法：

func someMethod(contextPtr: UnsafeMutablePointer<Void>)

我如何从中获取对象contextPtr？

func someMethod(contextPtr: UnsafeMutablePointer<Void>){    
    let object:MyObject = contextPtr.memory
}

给出：

“无效”不能转换为“ MyObject”

秘诀是什么

---

更多详情：

我实际上在这里正在为以下操作设置全局回调函数SCNetworkReachability：

func callback(reachability:SCNetworkReachability, flags: SCNetworkReachabilityFlags, info: UnsafeMutablePointer<Void>) {

    let r:Reachability = info.memory
}

然后添加回调，如下所示：

var context = SCNetworkReachabilityContext(version: 0, info: nil, retain: nil, release: nil, copyDescription: nil)
var s = self
withUnsafeMutablePointer(&s) {
    context.info = UnsafeMutablePointer($0)
}
SCNetworkReachabilitySetCallback(reachability, callback, &context)

Answer 1

这应该起作用：将对象指针作为不透明的非托管指针传递给回调：

context.info = UnsafeMutablePointer(Unmanaged.passUnretained(myObject).toOpaque())
SCNetworkReachabilitySetCallback(reachability, callback, &context)

并通过以下方式检索回调：

func callback(reachability:SCNetworkReachability, flags: SCNetworkReachabilityFlags, info: UnsafeMutablePointer<Void>) {

    let myObject = Unmanaged<MyObject>.fromOpaque(COpaquePointer(info)).takeUnretainedValue()

}

当然，这假定只要安装了回调，就存在对该对象的某些强引用，因此不会释放该对象。

更新： 请注意，如果您愿意使用“不安全”功能，则可以简化从对象指针到void指针以及返回的转换：

context.info = unsafeAddressOf(myObject)
// ...
myObject = unsafeBitCast(info, MyObject.self)

据我所知，生成的汇编代码是相同的。

更新2： 另请参阅如何快速将自身转换为UnsafeMutablePointer
<Void>类型，以获取有关“桥接”和此处可以使用的一些辅助函数的更多信息。

---

Swift 3更新（Xcode 8 beta 6）：

var context = SCNetworkReachabilityContext(version: 0, info: nil, retain: nil, release: nil, copyDescription: nil)
context.info = UnsafeMutableRawPointer(Unmanaged.passUnretained(self).toOpaque())

// ...

func callback(reachability:SCNetworkReachability, flags: SCNetworkReachabilityFlags, info: UnsafeMutableRawPointer?) {
    if let info = info {
        let myObject = Unmanaged<MyObject>.fromOpaque(info).takeUnretainedValue()
        // ...
    }
}