swift - 停止 dispatch_after

Question

我使用动画来指定提示，以帮助延迟交互:

 let delay = 1.8 * Double(NSEC_PER_SEC)
    let time = dispatch_time(DISPATCH_TIME_NOW, Int64(delay))
    dispatch_after(time, dispatch_get_main_queue()) {
        //call the method which have the steps after delay.

        self.rain.alpha = 0

        UIView.animateWithDuration(5, animations: {

            self.rain.alpha = 1

        })

        self.tip.startAnimating()

    }

但是，如果在动画开始之前，用户触摸了屏幕，我需要停止这个延迟过程。

Answer 1

iOS 8 和 OS X Yosemite 引入了 dispatch_block_cancel 允许您在它们开始执行之前取消它们

你在类中声明一个变量如下:

var block: dispatch_block_t?

初始化block变量并在dispatch_after中提供:

block = dispatch_block_create(DISPATCH_BLOCK_INHERIT_QOS_CLASS) {
  print("I executed")
}
let time: dispatch_time_t = dispatch_time(DISPATCH_TIME_NOW, Int64(5 * NSEC_PER_SEC))
dispatch_after(time, dispatch_get_main_queue(), block!)

之后您可以按如下方式取消它:

dispatch_block_cancel(block!)