迅捷2-UnsafeMutablePointer< Void>反对 [英] Swift 2 - UnsafeMutablePointer<Void> to object

问题描述

如果我有类似的方法:

func someMethod(contextPtr: UnsafeMutablePointer<Void>)

如何从contextPtr获取对象?

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

给予:

无效"不能转换为"MyObject"

'Void' is not convertible to 'MyObject'

秘诀是什么

更多细节:

我实际上在这里正在为SCNetworkReachability设置全局回调函数:

What I'm actually doing here is setting up a global callback function for 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:

and then adding the callback as follows:

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)

推荐答案

这应该起作用:将对象指针作为不透明的非托管指针传递 到回调:

This should work: pass the object pointer as an opaque unmanaged pointer to the callback:

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

并通过以下方式检索回调:

and retrieve in the callback via:

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

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

}

当然，这假定存在对该对象的一些强引用 只要安装了回调，就不会 释放.

Of course this assumes that some strong reference to the object exists as long as the callback is installed, so that the object is not deallocated.

更新:请注意，这两种从对象指针到空指针的转换 如果您愿意使用不安全"功能，则可以简化往返操作:

Update: Note that both conversions from object pointer to void pointer and back can be simplified if you are willing to use "unsafe" functions:

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

据我所见，生成的汇编代码是相同的.

The generated assembly code is – as far as I can see – identical.

更新2:另请参见如何将自己投射到UnsafeMutablePointer< Void>快速输入以获取更多信息 关于桥接"和一些可以在这里使用的辅助功能.

Update 2: See also How to cast self to UnsafeMutablePointer<Void> type in swift for more information about the "bridging" and some helper functions which can be used here.

迅速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()
        // ...
    }
}

这篇关于迅捷2-UnsafeMutablePointer&lt; Void&gt;反对的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！