Question

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
}

给出：

'Void'不能转换为'MyObject'

秘诀是什么

更多细节：

我在这里做的是为SCNetworkReachability设置全局回调函数：

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

    let r:Reachability = info.memory
}

然后按如下方式添加回调：

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

这应该工作：将对象指针作为不透明的非托管指针传递回调：

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，这假设存在对该对象的一些强引用只要安装了回调，那么对象就不会解除分配。

更新：请注意，从对象指针到void指针的转换如果你愿意使用＆＃34; unsafe＆＃34;功能：

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

生成的汇编代码 - 据我所见 - 相同。

更新2：有关详细信息，另请参阅How to cast self to UnsafeMutablePointer<Void> type in swift 关于＆＃34;桥接＆＃34;以及一些可以在这里使用的辅助函数。

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()
        // ...
    }
}

Answer 2

struct S {
    var i: Int = 10
}
var first = S()

func foo(contextPtr: UnsafeMutablePointer<Void>){
    let pS = UnsafeMutablePointer<S>(contextPtr)
    pS.memory.i = 100
}
print(first.i) // 10
foo(&first)
print(first.i) // 100

如果我们需要将UnsafeMutablePointer self传递给异步函数

import XCPlayground
XCPlaygroundPage.currentPage.needsIndefiniteExecution = true

import Foundation
// can be struct, class ...
class C {
    let queue = dispatch_queue_create("test", DISPATCH_QUEUE_CONCURRENT)
    var s: String = ""
    func foo() {
        var c = self
        dispatch_async(queue) { () -> Void in
            f(&c)
        }

    }
}

func f(pV: UnsafeMutablePointer<Void>) {
    let pC = UnsafeMutablePointer<C>(pV)
    sleep(1)
    print(pC.memory.s)
}

var c1: C? = C()
c1!.s = "C1"
c1!.foo()        // C1
var c2: C? = C()
c2!.s = "C2"
c2!.foo()        // C2
c1 = nil
c2 = nil
print("test")

Swift 2 - UnsafeMutablePointer <void>到对象

2 个答案: