斯威夫特：將數據傳遞到捕獲方面

Question

我試圖調用一個函數在恢復網絡連接時和updateOnConnection變量是真封閉。這裏是我的代碼：

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) 
} 

我的問題是，該行：

 if self.updateOnConnection { 
      self.refreshWallpaper() 
     } 

原因錯誤：「A C function pointer cannot be formed from a closure that captures context」

我不知道如何檢查的updateOnConnection和呼叫狀態refreshWallpaper()在閉包中監視互聯網連接的變化。我該如何解決這個問題，還是應該使用完全不同的解決方法？

Answer 1

在How to use instance method as callback for function which takes only func or literal closure相似，你必須 self轉換爲一個空指針，商店的背景下， 並將其轉換回一個對象指針在封閉：

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) 
} 

參見How to cast self to UnsafeMutablePointer<Void> type in swift 有關此機制的更多詳細信息。

注：if flags.rawValue == 0可表現稍微 優雅如if flags.isEmpty，但你實際上應該檢查 是if flags.contains(.Reachable)。

---

更新夫特3（Xcode的8個β6）：

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) 
}