取消 Swift 中的定时事件? [英] Cancel a timed event in Swift?

问题描述

我想在事件发生后的 10 秒内运行一段代码，但我希望能够取消它，这样如果在这 10 秒之前发生某些事情，代码将不会在 10 秒过去后运行.

I want to run a block of code in 10 seconds from an event, but I want to be able to cancel it so that if something happens before those 10 seconds, the code won't run after 10 seconds have gone by.

我一直在使用它，但它不能取消:

I've been using this, but it's not cancellable:

static func delay(delay:Double, closure:()->()) {
  dispatch_after(
    dispatch_time(
      DISPATCH_TIME_NOW,
      Int64(delay * Double(NSEC_PER_SEC))
    ),
    dispatch_get_main_queue(), closure
  )
}

我怎样才能做到这一点?

How can I accomplish this?

推荐答案

试试这个(Swift 2.x，请参阅下面 David 对 Swift 3 的回答):

Try this (Swift 2.x, see David's answer below for Swift 3):

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)
    }
}

// usage
let retVal = delay(2.0) {
    println("Later")
}
delay(1.0) {
    cancel_delay(retVal)
}

来自 Waam 的评论:dispatch_after - GCD in swift?

From Waam's comment here: dispatch_after - GCD in swift?

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