取消Swift中的定时事件？

试试看（Swift 2.x，请参阅下面有关Swift 3的David的回答）：

typealias dispatch_cancelable_closure = (cancel : Bool) -> ()func delay(time:NSTimeInterval, closure:()->()) ->  dispatch_cancelable_closure? {    func dispatch_later(clsr:()->()) {        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 let clsr = closure { if (cancel == false) {     dispatch_async(dispatch_get_main_queue(), clsr); }        }        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)    }}// usagelet retVal = delay(2.0) {    println("Later")}delay(1.0) {    cancel_delay(retVal)}