A magical bit of Swift (delay)

I recently had the need to delay a call, but only after a very slight delay.

I had a UITableView that when scrolled a certain way would resize itself, and I’d want to have it scroll to it’s top programmatically at that point. But I didn’t want the momentum of a user’s manipulation of the contentOffset to be so great as to make the scrolling to it’s top look out of place and abrupt.

I needed to gate the momentum generated by a user, so I’d want to delay the deactivation of scrollingEnabled. Not immediately, but just by a tiny bit.

I needed a way to do this kind of bizarre thing and found a wonderful bit of code online that does exactly what I want. If I could adjust the speed of setContentOffset:animated I could have done that (perhaps).

When I implemented it, it looked bizarre. It’s  a method inside of another method. The code around it isn’t exactly tight or anything, but the delay call is über cool.

func scrollViewDidScroll(scrollView: UIScrollView) {
    let py = scrollView.contentOffset.y
    if topCollapsed == false && py > 0 {
        topCollapsed = true
        var placeX:CGFloat = 25.0
        for subview in pvs {
            subview.changeToList(false)
            UIView.animateWithDuration(0.2, delay: 0.0, options: UIViewAnimationOptions.CurveLinear, animations: {
                    subview.center = CGPoint(x:placeX, y:25)
                }, completion: {
                    (finished: Bool) -> Void in
            })
            placeX = placeX + 53
         }

         delay(0.06){
            self.myTable.scrollEnabled = false
         }
         compressTop(true)
         ...

Here is that magical bit of code that delays whatever you’d like by a Double.

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

That’s pretty slick, right?