我的Xcode版本:6.3.2
Alamofire 版本:1.2.2(通过 Cocoapods 安装)
为了设置maxConcurrentOperationCount
限制并发操作数NSOperationQueue
,我包裹我的阿拉莫菲尔 https://github.com/Alamofire/AlamofireNSOperation 中的下载请求就像罗布建议的那样 https://stackoverflow.com/a/27022598/1576281.
的基本子类NSOperation
像这样:
class ConcurrentOperation : NSOperation {
override var concurrent: Bool {
return true
}
override var asynchronous: Bool {
return true
}
private var _executing: Bool = false
override var executing: Bool {
get {
return _executing
}
set {
if (_executing != newValue) {
self.willChangeValueForKey("isExecuting")
_executing = newValue
self.didChangeValueForKey("isExecuting")
}
}
}
private var _finished: Bool = false;
override var finished: Bool {
get {
return _finished
}
set {
if (_finished != newValue) {
self.willChangeValueForKey("isFinished")
_finished = newValue
self.didChangeValueForKey("isFinished")
}
}
}
/// Complete the operation
///
/// This will result in the appropriate KVN of isFinished and isExecuting
func completeOperation() {
executing = false
finished = true
}
override func start() {
if (cancelled) {
finished = true
return
}
executing = true
main()
}
}
我的子类包装了一个 Alamofire 下载请求,如下所示:
class DownloadImageOperation : ConcurrentOperation {
let URLString: String
let downloadImageCompletionHandler: (responseObject: AnyObject?, error: NSError?) -> ()
weak var request: Alamofire.Request?
init(URLString: String, downloadImageCompletionHandler: (responseObject: AnyObject?, error: NSError?) -> ()) {
self.URLString = URLString
self.downloadImageCompletionHandler = downloadImageCompletionHandler
super.init()
}
override func main() {
let destination = Alamofire.Request.suggestedDownloadDestination(directory: .DocumentDirectory, domain: .UserDomainMask)
request = Alamofire.download(.GET, URLString, destination).response { (request, response, responseObject, error) in
if self.cancelled {
println("Alamofire.download cancelled while downlading. Not proceed.")
} else {
self.downloadImageCompletionHandler(responseObject: responseObject, error: error)
}
self.completeOperation()
}
}
override func cancel() {
request?.cancel()
super.cancel()
}
}
它覆盖cancel()
并尝试取消 Alamofire 请求NSOperation
取消。
我使用 KVO 观察者来观察完成NSOperationQueue
.
private var testAlamofireContext = 0
class TestAlamofireObserver: NSObject {
var queue = NSOperationQueue()
init(delegate: ImageDownloadDelegate) {
super.init()
queue.addObserver(self, forKeyPath: "operations", options: .New, context: &testAlamofireContext)
}
deinit {
queue.removeObserver(self, forKeyPath: "operations", context: &testAlamofireContext)
}
override func observeValueForKeyPath(keyPath: String, ofObject object: AnyObject, change: [NSObject: AnyObject], context: UnsafeMutablePointer<Void>) {
if context == &testAlamofireContext {
if self.queue.operations.count == 0 {
println("Image Download Complete queue. keyPath: \(keyPath); object: \(object); context: \(context)")
}
} else {
super.observeValueForKeyPath(keyPath, ofObject: object, change: change, context: context)
}
}
}
我开始了这样的下载列表:
func downloadImages() {
let imgLinks = [
"https://farm4.staticflickr.com/3925/18769503068_1fc09427ec_k.jpg",
"https://farm1.staticflickr.com/338/18933828356_4f57420df7_k.jpg",
"https://farm4.staticflickr.com/3776/18945113685_ccec89d67a_o.jpg",
"https://farm1.staticflickr.com/366/18333992053_725f21166e_k.jpg",
"https://farm4.staticflickr.com/3777/18962702032_086453ee7a_k.jpg",
"https://farm1.staticflickr.com/373/18930501406_4753ac021a_k.jpg",
"https://farm1.staticflickr.com/283/18772907409_56ffbe573b_k.jpg",
"https://farm1.staticflickr.com/314/18940901785_b0564b1c9b_o.jpg",
"https://farm1.staticflickr.com/502/18949263495_88d75d2d2f_k.jpg",
"https://farm4.staticflickr.com/3912/18938184302_6e0ca9ad31_k.jpg",
"https://farm1.staticflickr.com/356/18957923475_3dc9df7634_k.jpg",
"https://farm1.staticflickr.com/378/18925014986_e87feca9c7_o.jpg",
"https://farm1.staticflickr.com/461/18949863812_ddf700bd03_o.jpg",
"https://farm1.staticflickr.com/303/18920711216_4684ff4295_k.jpg",
"https://farm1.staticflickr.com/558/18935058546_fc10d10855_k.jpg",
"https://farm1.staticflickr.com/384/18955290345_fb93d17828_o.jpg",
"https://farm1.staticflickr.com/366/18333992053_725f21166e_k.jpg",
"https://farm4.staticflickr.com/3777/18962702032_086453ee7a_k.jpg",
"https://farm1.staticflickr.com/373/18930501406_4753ac021a_k.jpg",
"https://farm1.staticflickr.com/283/18772907409_56ffbe573b_k.jpg",
"https://farm1.staticflickr.com/314/18940901785_b0564b1c9b_o.jpg",
"https://farm1.staticflickr.com/502/18949263495_88d75d2d2f_k.jpg",
"https://farm4.staticflickr.com/3912/18938184302_6e0ca9ad31_k.jpg",
"https://farm1.staticflickr.com/356/18957923475_3dc9df7634_k.jpg",
"https://farm1.staticflickr.com/378/18925014986_e87feca9c7_o.jpg",
"https://farm1.staticflickr.com/461/18949863812_ddf700bd03_o.jpg",
"https://farm1.staticflickr.com/303/18920711216_4684ff4295_k.jpg",
"https://farm1.staticflickr.com/558/18935058546_fc10d10855_k.jpg",
"https://farm1.staticflickr.com/366/18333992053_725f21166e_k.jpg",
"https://farm4.staticflickr.com/3777/18962702032_086453ee7a_k.jpg",
"https://farm1.staticflickr.com/373/18930501406_4753ac021a_k.jpg",
"https://farm1.staticflickr.com/283/18772907409_56ffbe573b_k.jpg",
"https://farm1.staticflickr.com/314/18940901785_b0564b1c9b_o.jpg",
"https://farm1.staticflickr.com/502/18949263495_88d75d2d2f_k.jpg",
"https://farm4.staticflickr.com/3912/18938184302_6e0ca9ad31_k.jpg",
"https://farm1.staticflickr.com/356/18957923475_3dc9df7634_k.jpg",
"https://farm1.staticflickr.com/378/18925014986_e87feca9c7_o.jpg",
"https://farm1.staticflickr.com/461/18949863812_ddf700bd03_o.jpg",
"https://farm1.staticflickr.com/303/18920711216_4684ff4295_k.jpg",
"https://farm1.staticflickr.com/558/18935058546_fc10d10855_k.jpg",
"https://farm4.staticflickr.com/3777/18962702032_086453ee7a_k.jpg",
"https://farm1.staticflickr.com/373/18930501406_4753ac021a_k.jpg",
"https://farm1.staticflickr.com/283/18772907409_56ffbe573b_k.jpg",
"https://farm1.staticflickr.com/314/18940901785_b0564b1c9b_o.jpg",
"https://farm1.staticflickr.com/502/18949263495_88d75d2d2f_k.jpg",
"https://farm4.staticflickr.com/3912/18938184302_6e0ca9ad31_k.jpg",
"https://farm1.staticflickr.com/356/18957923475_3dc9df7634_k.jpg",
"https://farm1.staticflickr.com/378/18925014986_e87feca9c7_o.jpg",
"https://farm1.staticflickr.com/461/18949863812_ddf700bd03_o.jpg",
"https://farm1.staticflickr.com/303/18920711216_4684ff4295_k.jpg",
"https://farm1.staticflickr.com/558/18935058546_fc10d10855_k.jpg",
"https://farm1.staticflickr.com/266/18956724112_6e61a743a5_k.jpg"
]
var testAlamofireObserver = TestAlamofireObserver()
testAlamofireObserver!.queue.maxConcurrentOperationCount = 5
for imgLink in imgLinks {
let operation = DownloadImageOperation(URLString: imgLink) {
(responseObject, error) in
if responseObject == nil {
// handle error here
println("failed: \(error)")
} else {
println("\(responseObject?.absoluteString) downloaded.")
}
}
testAlamofireObserver!.queue.addOperation(operation)
}
}
如果队列完成而没有收到任何取消,则日志输出应为:
2015-06-22 17:11:04.206 RSS Wallpaper Switchr[46250:714702] Optional(Optional("https://farm1.staticflickr.com/461/18949863812_ddf700bd03_o.jpg")) downloaded.
...
...
...
2015-06-22 17:11:56.979 RSS Wallpaper Switchr[46250:714702] Optional(Optional("https://farm1.staticflickr.com/461/18949863812_ddf700bd03_o.jpg")) downloaded.
2015-06-22 17:11:56.979 RSS Wallpaper Switchr[46250:714702] Image Download Complete queue. keyPath: operations; object: <NSOperationQueue: 0x6180002354a0>{name = 'NSOperationQueue 0x6180002354a0'}; context: 0x000000010007eb70
如果队列收到cancelAllOperations()
,日志输出应该是:
2015-06-22 17:16:29.691 RSS Wallpaper Switchr[46467:720630] Optional(Optional("https://farm1.staticflickr.com/366/18333992053_725f21166e_k.jpg")) downloaded.
2015-06-22 17:16:32.632 RSS Wallpaper Switchr[46467:720630] Alamofire.download cancelled while downlading. Not proceed.
...
...
2015-06-22 17:16:32.642 RSS Wallpaper Switchr[46467:720630] Alamofire.download cancelled while downlading. Not proceed.
2015-06-22 17:16:32.643 RSS Wallpaper Switchr[46467:720630] Image Download Complete queue. keyPath: operations; object: <NSOperationQueue: 0x600000024c20>{name = 'NSOperationQueue 0x600000024c20'}; context: 0x000000010007eb70
然而,如果我改变了maxConcurrentOperationCount
如上所述的非默认值,并且队列接收cancelAllOperations()
,日志变成:
2015-06-22 17:17:56.427 RSS Wallpaper Switchr[46606:722523] Optional(Optional("https://farm4.staticflickr.com/3777/18962702032_086453ee7a_k.jpg")) downloaded.
2015-06-22 17:17:58.675 RSS Wallpaper Switchr[46606:722523] Alamofire.download cancelled while downlading. Not proceed.
...
...
2015-06-22 17:17:58.677 RSS Wallpaper Switchr[46606:722523] Alamofire.download cancelled while downlading. Not proceed.
2015-06-22 17:17:58.678 RSS Wallpaper Switchr[46606:722720] Image Download Complete queue. keyPath: operations; object: <NSOperationQueue: 0x608000424ee0>{name = 'NSOperationQueue 0x608000424ee0'}; context: 0x000000010007eb70
2015-06-22 17:17:58.678 RSS Wallpaper Switchr[46606:722560] Image Download Complete queue. keyPath: operations; object: <NSOperationQueue: 0x608000424ee0>{name = 'NSOperationQueue 0x608000424ee0'}; context: 0x000000010007eb70
2015-06-22 17:17:58.678 RSS Wallpaper Switchr[46606:722574] Image Download Complete queue. keyPath: operations; object: <NSOperationQueue: 0x608000424ee0>{name = 'NSOperationQueue 0x608000424ee0'}; context: 0x000000010007eb70
2015-06-22 17:17:58.678 RSS Wallpaper Switchr[46606:722719] Image Download Complete queue. keyPath: operations; object: <NSOperationQueue: 0x608000424ee0>{name = 'NSOperationQueue 0x608000424ee0'}; context: 0x000000010007eb70
2015-06-22 17:17:58.678 RSS Wallpaper Switchr[46606:722721] Image Download Complete queue. keyPath: operations; object: <NSOperationQueue: 0x608000424ee0>{name = 'NSOperationQueue 0x608000424ee0'}; context: 0x000000010007eb70
2015-06-22 17:17:58.678 RSS Wallpaper Switchr[46606:722572] Image Download Complete queue. keyPath: operations; object: <NSOperationQueue: 0x608000424ee0>{name = 'NSOperationQueue 0x608000424ee0'}; context: 0x000000010007eb70
The KVO observeValueForKeyPath
从多个不同的线程执行。线程的数量可以是可变的。这将导致KVO的完成函数被执行多次。如果我不更改默认值,这种情况就不会发生maxConcurrentOperationCount
或不request?.cancel()
for Alamofire.Request
.
为什么我关心 KVO 完成函数的多次执行?我的目的是启动一个下载队列,当足够的下载完成时,取消剩余的操作,即使是未启动的或正在下载的操作,然后为下载做一些事情。完成函数应该只执行一次,两个因素 (1) 改变了默认值maxConcurrentOperationCount
(2) 不request?.cancel()
for Alamofire.Request
可能与此有关。我想知道为什么以及如何纠正这个问题。