Swift：将数据传递给捕获上下文的闭包 [英] Swift: Pass data to a closure that captures context

问题描述

我尝试在互联网连接恢复并且 updateOnConnection 变量为true时调用函数。这是我的代码：

  func checkForConnection（）{
 let host =reddit.com
 var context = SCNetworkReachabilityContext（version：0，info：nil，retain：nil，release：nil，copyDescription：nil）
 let reachability = SCNetworkReachabilityCreateWithName（nil，host）！ 
 
如果flags.rawValue == 0，则
中的SCNetworkReachabilitySetCallback（可达性，{（_，flags，_））// {//未连接互联网
 
} else { // internet connected connected 
 if self.updateOnConnection {
 self.refreshWallpaper（）
} 
} 
}，& context）
 
 SCNetworkReachabilityScheduleWithRoLoop（reachability，CFRunLoopGetMain（），kCFRunLoopCommonModes）
} 
  

我的问题是行：

  if self.updateOnConnection {
 self.refreshWallpaper（）
} 
  

导致错误： AC函数指针不能从捕获上下文的闭包形成

我不知道如何检查 updateOnConnection 的状态，并调用 refreshWallpaper（）在闭包中监视互联网连接的变化。如何解决这个问题，或者有一个完全不同的解决方法，我应该使用？

解决方案 http://stackoverflow.com/questions/33260808/swift-proper-use-of-cfnotificationcenteraddobserver-w-callback\">Swift - 正确使用CFNotificationCenterAddObserver w /回调，您必须转换
self 到一个void指针，将其存储在上下文中，
并将其转换回闭包中的一个对象指针：

  func checkForConnection（）{
 
 let host =reddit.com
 var context = SCNetworkReachabilityContext ：nil，retain：nil，release：nil，copyDescription：nil）
 context.info = UnsafeMutablePointer（Unmanaged.passUnretained（self）.toOpaque（））
 
 let reachability = SCNetworkReachabilityCreateWithName ，主机）！ 
 
如果flags.rawValue == 0，则
中的SCNetworkReachabilitySetCallback（可达性，{（_，flags，info））// {//未连接互联网
 
} else { // internet已连接
 let mySelf = Unmanaged< ViewController> .fromOpaque（COpaquePointer（info））。takeUnretainedValue（）
 
如果mySelf.updateOnConnection {
 mySelf.refreshWallpaper 
} 
} 
}，& context）
 
 SCNetworkReachabilityScheduleWithRoLoop（reachability，CFRunLoopGetMain（），kCFRunLoopCommonModes）
} 
  

另请参阅如何将self转换为UnsafeMutablePointer< Void>请键入swift
以了解有关此机制的更多详细信息。

备注： if flags .rawValue == 0 可以表示稍微多一些
优雅为如果flags.isEmpty ，但实际上<如果flags.contains（.Reachable）。

---

更新Swift 3（Xcode 8 beta 6）：

  func checkForConnection（）{
 
 let host =reddit.com
 var context = SCNetworkReachabilityContext（version：0，info：nil，retain：nil，release：nil，copyDescription：nil）
 context.info = UnsafeMutableRawPointer（Unmanaged.passUnretained（self）.toOpaque（））
 
 let reachability = SCNetworkReachabilityCreateWithName（nil，host）！ 
 
在
中的SCNetworkReachabilitySetCallback（reachability，{（_，flags，info）如果let info = info {
 if flags.rawValue == 0 {// internet is not connected 
 
} else {// internet become connected 
 let mySelf = Unmanaged< ViewController> .fromOpaque（info）.takeUnretainedValue（）
 // ... 
} 
} 
}，& context）
 
 SCNetworkReachabilityScheduleWithRunLoop（reachability，CFRunLoopGetMain（），CFRunLoopMode.commonModes.rawValue）
} 
  

I am trying to call a function when the internet connection is restored and the updateOnConnection variable is true. Here is my code:

func checkForConnection() {
    let host = "reddit.com"
    var context = SCNetworkReachabilityContext(version: 0, info: nil, retain: nil, release: nil, copyDescription: nil)
    let reachability = SCNetworkReachabilityCreateWithName(nil, host)!

    SCNetworkReachabilitySetCallback(reachability, { (_, flags, _) in
        if flags.rawValue == 0 { //internet is not connected

        } else { //internet became connected
            if self.updateOnConnection {
                self.refreshWallpaper()
            }
        }
    }, &context)

    SCNetworkReachabilityScheduleWithRunLoop(reachability, CFRunLoopGetMain(), kCFRunLoopCommonModes)
}

My problem is that the lines:

        if self.updateOnConnection {
            self.refreshWallpaper()
        }

cause the error: "A C function pointer cannot be formed from a closure that captures context"

I am not sure how to check the state of updateOnConnection and call refreshWallpaper() in the closure that monitors changes in the internet connection. How can I fix this, or is there a totally different workaround I should be using?

解决方案

Similar as in Swift - Proper use of CFNotificationCenterAddObserver w/callback, you have to convert self to a void pointer, store that in the context, and convert it back to an object pointer in the closure:

func checkForConnection() {

    let host = "reddit.com"
    var context = SCNetworkReachabilityContext(version: 0, info: nil, retain: nil, release: nil, copyDescription: nil)
    context.info = UnsafeMutablePointer(Unmanaged.passUnretained(self).toOpaque())

    let reachability = SCNetworkReachabilityCreateWithName(nil, host)!

    SCNetworkReachabilitySetCallback(reachability, { (_, flags, info) in
        if flags.rawValue == 0 { //internet is not connected

        } else { //internet became connected
            let mySelf = Unmanaged<ViewController>.fromOpaque(COpaquePointer(info)).takeUnretainedValue()

            if mySelf.updateOnConnection {
                mySelf.refreshWallpaper()
            }
        }
        }, &context)

    SCNetworkReachabilityScheduleWithRunLoop(reachability, CFRunLoopGetMain(), kCFRunLoopCommonModes)
}

See also How to cast self to UnsafeMutablePointer<Void> type in swift for more details about this mechanism.

Remark: if flags.rawValue == 0 can be expressed slightly more elegant as if flags.isEmpty, but what you actually should check is if flags.contains(.Reachable).

---

Update for Swift 3 (Xcode 8 beta 6):

func checkForConnection() {

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

    let reachability = SCNetworkReachabilityCreateWithName(nil, host)!

    SCNetworkReachabilitySetCallback(reachability, { (_, flags, info) in
        if let info = info {
            if flags.rawValue == 0 { //internet is not connected

            } else { //internet became connected
                let mySelf = Unmanaged<ViewController>.fromOpaque(info).takeUnretainedValue()
                // ...
            }
        }
    }, &context)

    SCNetworkReachabilityScheduleWithRunLoop(reachability, CFRunLoopGetMain(), CFRunLoopMode.commonModes.rawValue)
}

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