停止dispatch_after [英] Stop dispatch_after

问题描述

我使用动画来指定提示，以帮助延迟交互，方法如下：

I use an animation for specify a tip to help the interaction with delay using these:

 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屏幕，我需要停止此延迟过程。

But, I need to stop this delay process if, before animation start, user touch the screen.

推荐答案

iOS 8和OS X Yosemite引入了 dispatch_block_cancel ，可让您在开始执行之前取消它们

iOS 8 and OS X Yosemite introduced dispatch_block_cancel that allow you to cancel them before they start executing

您在类中声明了一个变量，如下所示：

You declare one variable in class as follows:

var block: dispatch_block_t?

初始化 block 变量并将其提供在 dispatch_after ：

Init block variable and provide it in dispatch_after:

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，您可以按以下步骤取消它：

After that you can cancel it as follows:

dispatch_block_cancel(block!)

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