如何使用實例方法作為只接受func或文字閉包的函數(shù)的回調(diào)在“ViewController.swift”中我創(chuàng)建了這個回調(diào)：func callback(cf:CFNotificationCenter!,
ump:UnsafeMutablePointer<Void>,
cfs:CFString!,
up:UnsafePointer<Void>,
cfd:CFDictionary!) -> Void {}使用此觀察者：CFNotificationCenterAddObserver(CFNotificationCenterGetDarwinNotifyCenter(),
nil,
self.callback,
"myMESSage",
nil,
CFNotificationSuspensionBehavior.DeliverImmediately)導(dǎo)致此編譯器錯誤：“AC函數(shù)指針只能通過對'func'或文字閉包的引用形成”
2 回答
犯罪嫌疑人X
TA貢獻(xiàn)2080條經(jīng)驗 獲得超4個贊
回調(diào)是指向C函數(shù)的指針，在Swift中，您只能傳遞全局函數(shù)或閉包（不捕獲任何狀態(tài)），但不能傳遞實例方法。
所以這確實有效：
CFNotificationCenterAddObserver(CFNotificationCenterGetDarwinNotifyCenter(),
nil,
{ (_, observer, name, _, _) in
print("received notification: \(name)")
},
"myMessage",
nil,
.DeliverImmediately)但由于閉包無法捕獲上下文，因此您無法直接引用self其屬性和實例方法。例如，您無法添加
self.label.stringValue = "got it"// error: a C function pointer cannot be formed from a closure that captures context
在閉包內(nèi)部，在通知到達(dá)時更新UI。
有一個解決方案，但由于Swift嚴(yán)格的類型系統(tǒng)，它有點復(fù)雜。與Swift 2 - UnsafeMutablePointer <Void>中的對象類似，您可以將指針轉(zhuǎn)換 self為void指針，將其作為observer參數(shù)傳遞給注冊，并將其轉(zhuǎn)換回回調(diào)中的對象指針。
class YourClass {
func callback(name : String) {
print("received notification: \(name)")
}
func registerObserver() {
// Void pointer to `self`:
let observer = UnsafePointer<Void>(Unmanaged.passUnretained(self).toOpaque())
CFNotificationCenterAddObserver(CFNotificationCenterGetDarwinNotifyCenter(),
observer,
{ (_, observer, name, _, _) -> Void in
// Extract pointer to `self` from void pointer:
let mySelf = Unmanaged<YourClass>.fromOpaque(
COpaquePointer(observer)).takeUnretainedValue()
// Call instance method:
mySelf.callback(name as String)
},
"myMessage",
nil,
.DeliverImmediately)
}
// ...}閉包充當(dāng)實例方法的“蹦床”。
指針是未保留的引用，因此必須確保在取消分配對象之前刪除觀察者。
Swift 3更新：
class YourClass {
func callback(_ name : String) {
print("received notification: \(name)")
}
func registerObserver() {
// Void pointer to `self`:
let observer = UnsafeRawPointer(Unmanaged.passUnretained(self).toOpaque())
CFNotificationCenterAddObserver(CFNotificationCenterGetDarwinNotifyCenter(),
observer,
{ (_, observer, name, _, _) -> Void in
if let observer = observer, let name = name {
// Extract pointer to `self` from void pointer:
let mySelf = Unmanaged<YourClass>.fromOpaque(observer).takeUnretainedValue()
// Call instance method:
mySelf.callback(name.rawValue as String)
}
},
"myMessage" as CFString,
nil,
.deliverImmediately)
}
// ...}有關(guān)對象指針和C指針之間“橋接”的更多信息，另請參見如何將self轉(zhuǎn)換為UnsafeMutablePointer <Void>鍵入swift。
慕田峪4524236
TA貢獻(xiàn)1875條經(jīng)驗 獲得超5個贊
在我的例子中，我想從我的閉包中調(diào)用的函數(shù)是在AppDelegate中。所以我能夠使用委托從閉包中調(diào)用函數(shù)而不使用self。這是否是一個好主意是具有更多經(jīng)驗的人必須評論的東西。
self.pingSocket = CFSocketCreate(kCFAllocatorDefault, AF_INET, SOCK_DGRAM, IPPROTO_ICMP,CFSocketCallBackType.dataCallBack.rawValue, {socket, type, address, data, info in
//type is CFSocketCallBackType
guard let socket = socket, let address = address, let data = data, let info = info else { return }// stuff deleted, including use of C pointers
let appDelegate = NSApplication.shared.delegate as! AppDelegate
appDelegate.receivedPing(ip: sourceIP, sequence: sequence, id: id)
//}
return
}, &context)extension AppDelegate: ReceivedPingDelegate {
func receivedPing(ip: UInt32, sequence: UInt16, id: UInt16) {
// stuff deleted
}}protocol ReceivedPingDelegate: class {
func receivedPing(ip: UInt32, sequence: UInt16, id: UInt16)}- 2 回答
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