在斯威夫特的GCD后派人去吗？

Question

在斯威夫特的GCD后派人去吗？

我经历了iBook来自苹果，却找不到它的任何定义：

有人能解释一下…的结构吗？dispatch_after?

dispatch_after(<#when: dispatch_time_t#>, <#queue: dispatch_queue_t?#>, <#block: dispatch_block_t?#>)

Answer 1

我用dispatch_after通常，我编写了一个顶级实用程序函数来简化语法：func delay(delay:Double, closure:()->()) {     dispatch_after(         dispatch_time(             DISPATCH_TIME_NOW,             Int64(delay * Double(NSEC_PER_SEC))         ),         dispatch_get_main_queue(), closure)}现在你可以这样说话了：delay(0.4) {     // do stuff}哇，一种你可以提高语言的语言。还有比这更好的吗？更新SWIFT 3，Xcode 8种子6既然它们已经改进了调用语法，似乎几乎不值得去费心：func delay(_ delay:Double, closure:@escaping ()->()) {     let when = DispatchTime.now() + delay    DispatchQueue.main.asyncAfter(deadline: when, execute: closure)}

Answer 2

为了扩展Cezary的答案，它将在1纳秒后执行，我必须在4秒半后执行以下操作。let delay = 4.5 * Double(NSEC_PER_SEC)let time = dispatch_time(DISPATCH_TIME_NOW, Int64(delay))dispatch_after(time, dispatch_get_main_queue(),  block)编辑：我发现我的原始代码稍有错误。如果不将nsec_per_sec强制转换为Double，则隐式类型将导致编译错误。如果有人能提出更好的解决方案，我很想听听。=SWIFT 3的更新=在SWIFT 3中，这是非常简单和优雅的：DispatchQueue.main.asyncAfter(deadline: .now() + 4.5) {     // ...}

Answer 3

如果需要使该块失效，您可能需要使用以下命令：typealias dispatch_cancelable_closure = (cancel : Bool) -> Voidfunc delay(time:NSTimeInterval, closure:()->Void) ->  dispatch_cancelable_closure? {     func dispatch_later(clsr:()->Void) {         dispatch_after(             dispatch_time(                 DISPATCH_TIME_NOW,                 Int64(time * Double(NSEC_PER_SEC))             ),             dispatch_get_main_queue(), clsr)     }     var closure:dispatch_block_t? = closure    var cancelableClosure:dispatch_cancelable_closure?     let delayedClosure:dispatch_cancelable_closure = { cancel in         if closure != nil {             if (cancel == false) {                 dispatch_async(dispatch_get_main_queue(), closure!);             }         }         closure = nil         cancelableClosure = nil     }     cancelableClosure = delayedClosure     dispatch_later {         if let delayedClosure = cancelableClosure {             delayedClosure(cancel: false)         }     }     return cancelableClosure;}func cancel_delay(closure:dispatch_cancelable_closure?) {     if closure != nil {         closure!(cancel: true)     }}用途如下let retVal = delay(2.0) {     println("Later")}delay(1.0) {     cancel_delay(retVal)}学分