Swift - 正确使用CFNotificationCenterAddObserver w /回调
问题描述
in'ViewController.swift'
创建此回调：
func callback（cf：CFNotificationCenter !, ump：UnsafeMutablePointer< Void>， cfs：CFString !, up：UnsafePointer< Void> ;, cfd：CFDictionary！ - >无效{ } 使用此观察者：
CFNotificationCenterAddObserver（CFNotificationCenterGetDarwinNotifyCenter（）， nil， self.callback，myMESSage， CFNotificationSuspensionBehavior.DeliverImmediately） 导致此编译器错误：
AC函数指针只能通过引用一个'func'或一个文字闭包而形成
想法？
c中的CFNotificationCenterAddObserver（CFNotificationCenterGetDarwinNotifyCenter（），
nil，
{（_，observer，name，_，_）print（received notification：\（name） $ b}，
myMessage，
nil，
.DeliverImmediately）
$ b b
但是因为闭包不能捕获上下文，所以没有直接引用 self 及其属性和实例方法。
例如，您不能添加
self.label.stringValue =got it //错误：不能从捕获上下文的闭包形成C函数指针 当一个通知到达时，UI。
有一个解决方案，但由于
Swift的严格类型系统，它有点复杂。
类似于 Swift 2 - UnsafeMutablePointer< Void>到对象，你可以将指针转换为self 为void指针，传递 observer 参数
到注册，并将其转换回
中的对象指针回调。
class YourClass { func callback（name：String）{ print（received notification：\（name））} func registerObserver（）{ //指向`self`的void指针： let observer = UnsafePointer< Void>（Unmanaged.passUnretained（self）.toOpaque（）） CFNotificationCenterAddObserver（CFNotificationCenterGetDarwinNotifyCenter（）， observer， {（_，observer，name，_，_） - > Void in //提取指针从void指针到`self`： let mySelf = Unmanaged< YourClass> .fromOpaque（ COpaquePointer（observer））。takeUnretainedValue（） //调用实例方法： mySelf .callback（name as String）}，myMessage， nil， .DeliverImmediately）} // .. } 闭包作为实例方法的trampoline / p>
指针是一个未保存的引用，因此必须确保
在释放对象之前被移除。
更新Swift 3：
class YourClass { func callback（_ name：String）{ print（received notification：\（name））} func registerObserver（）{ //指向`self`的指针： let observer = UnsafeRawPointer（Unmanaged.passUnretained（self）.toOpaque（）） CFNotificationCenterAddObserver（CFNotificationCenterGetDarwinNotifyCenter（）， observer， {（_，observer，name，_，_） - > 如果let observer = observer，则let name = name { // void void指针指向`self`指针： let mySelf =非托管< YourClass> .fromOpaque （观察者）.takeUnretainedValue（） //调用实例方法： mySelf.callback（name.rawValue as String）} }，myMessageas CFString， nil， .deliverImmediately）} // ... }
in 'ViewController.swift'
Creating this callback:
func callback(cf:CFNotificationCenter!,
ump:UnsafeMutablePointer<Void>,
cfs:CFString!,
up:UnsafePointer<Void>,
cfd:CFDictionary!) -> Void {
}
Using this observer:
CFNotificationCenterAddObserver(CFNotificationCenterGetDarwinNotifyCenter(),
nil,
self.callback,
"myMESSage",
nil,
CFNotificationSuspensionBehavior.DeliverImmediately)
Results in this compiler error: "A C function pointer can only be formed from a reference to a 'func' or a literal closure"
Thoughts?
The callback is a pointer to a C function, and in Swift you can pass only a global function or a closure (which does not capture any state), but not an instance method.
So this does work:
CFNotificationCenterAddObserver(CFNotificationCenterGetDarwinNotifyCenter(),
nil,
{ (_, observer, name, _, _) in
print("received notification: \(name)")
},
"myMessage",
nil,
.DeliverImmediately)
But since the closure cannot capture context, you have no direct reference to self and its properties and instance methods. For example, you cannot add
self.label.stringValue = "got it"
// error: a C function pointer cannot be formed from a closure that captures context
inside the closure to update the UI when a notification arrived.
There is a solution, but it is a little bit complicated due to Swift's strict type system. Similarly as in Swift 2 - UnsafeMutablePointer<Void> to object, you can convert the pointer to self to a void pointer, pass that as the observer parameter to the registration, and convert it back to an object pointer in the callback.
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)
}
// ...
}
The closure acts as a "trampoline" to the instance method.
The pointer is an unretained reference, therefore you must ensure that the observer is removed before the object is deallocated.
Update for Swift 3:
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)
}
// ...
}
Update for Swift 5:
发送通知
sendNotificationForMessageWithIdentifier(identifier: "broadcastStarted")
func sendNotificationForMessageWithIdentifier(identifier : String) {
let center : CFNotificationCenter = CFNotificationCenterGetDarwinNotifyCenter()
// let userInfo : CFDictionary = CFDictionary(info)
let identifierRef : CFNotificationName = CFNotificationName(identifier as CFString)
CFNotificationCenterPostNotification(center, identifierRef, nil, nil, true)
}
///通知回调
func callback(_ name : String) {
print("received notification: \(name)")
mainView.vedioV.uploadBtn.isHidden = false
///视频预览
DispatchQueue.main.asyncAfter(deadline: .now() + 1) { [weak self] in
let userDefault = UserDefaults.init(suiteName: "group.dc.record")
let pathstr = userDefault?.object(forKey: "videoFilePath")
guard let path = pathstr else {
return
}
self?.vm.urlVedioString = URL(fileURLWithPath: path as! String)
self?.mainView.vedioV.loadImageReview(url: URL(fileURLWithPath: path as! String))
}
}
///通知注册
func registerObserver() {
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<OTCAppealVC>.fromOpaque(observer).takeUnretainedValue()
// Call instance method:
mySelf.callback(name.rawValue as String)
}
},
"broadcastFinished" as CFString,
nil,
.deliverImmediately)
}
通知移除
deinit {
let observer = UnsafeRawPointer(Unmanaged.passUnretained(self).toOpaque())
let cfName: CFNotificationName = CFNotificationName("broadcastFinished" as CFString)
CFNotificationCenterRemoveObserver(CFNotificationCenterGetDarwinNotifyCenter(), observer, cfName, nil)
}
