如何检测UIScrollView何时完成滚动在Swift中

Question

从各方面来看，Ashley Smart（How to detect when a UIScrollView has finished scrolling）提出的Obj-C中的这个问题是一个很好的解决方案。

-(void)scrollViewDidScroll:(UIScrollView *)sender 
{   
[NSObject cancelPreviousPerformRequestsWithTarget:self];
    //ensure that the end of scroll is fired.
    [self performSelector:@selector(scrollViewDidEndScrollingAnimation:) withObject:nil afterDelay:0.3]; 

...
}

-(void)scrollViewDidEndScrollingAnimation:(UIScrollView *)scrollView
{
    [NSObject cancelPreviousPerformRequestsWithTarget:self];
...
}

但是，我需要一个解决方案，在Swift中。

似乎由Matt（dispatch_after - GCD in swift?）贡献的优秀延迟功能可能会有所帮助。

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

并实施为......

delay(0.4) {
    // do stuff
}

但我还是没把它放在一起。有帮助吗？

Answer 1

委托方法告诉您何时完成

func scrollViewDidEndDecelerating(scrollView: UIScrollView) {
    self.stoppedScrolling()
}

func scrollViewDidEndDragging(scrollView: UIScrollView, willDecelerate decelerate: Bool) {
    if !decelerate {
        self.stoppedScrolling()
    }
}

func stoppedScrolling() {
    println("Scroll finished")
}

Answer 2

如果用户缓慢滚动，则不会调用scrollViewDidEndDecelerating。这是斯威夫特的Ashley Smart asnwear

func scrollViewDidScroll(_ scrollView: UIScrollView) {
    NSObject.cancelPreviousPerformRequests(withTarget: self)
    perform(#selector(UIScrollViewDelegate.scrollViewDidEndScrollingAnimation), with: nil, afterDelay: 0.3)
}

func scrollViewDidEndScrollingAnimation(_ scrollView: UIScrollView) {
    NSObject.cancelPreviousPerformRequests(withTarget: self)
// Call your function here
}

Answer 3

有一种UIScrollViewDelegate的方法可以用来检测（或更好地说'预测'）滚动真的完成时：

func scrollViewWillEndDragging(_ scrollView: UIScrollView, withVelocity velocity: CGPoint, targetContentOffset: UnsafeMutablePointer<CGPoint>)

当滚动真的完成时，UIScrollViewDelegate可用于检测（或更好地说'预测'）。

在我的情况下，我使用水平滚动如下（在Swift 3中）：

func scrollViewWillEndDragging(_ scrollView: UIScrollView, withVelocity velocity: CGPoint, targetContentOffset: UnsafeMutablePointer<CGPoint>) {
    perform(#selector(self.actionOnFinishedScrolling), with: nil, afterDelay: Double(velocity.x))
}
func actionOnFinishedScrolling() {
    print("scrolling is finished")
    // do what you need
}

Answer 4

您需要检查用户是否已停止拖动，以及在用户停止拖动后视图是否仍在减速：

func scrollViewDidEndDragging(_ scrollView: UIScrollView, willDecelerate decelerate: Bool) {
    if collectionView.isDecelerating == false {
        // Perform whichever function you desire for when scrolling has stopped
    }
}

func scrollViewDidEndDecelerating(_ scrollView: UIScrollView) {
    // Perform whichever function you desire for when scrolling has stopped
}

Answer 5

Swift版本：

注意：您提到的答案是可能的解决方案，因案例而异

func scrollViewDidScroll(_ scrollView: UIScrollView) {

        // YOUR CODE........
        NSObject.cancelPreviousPerformRequests(withTarget: self)
        self.perform(#selector(scrollViewDidEndScrollingAnimation(_:)), with: scrollView, afterDelay: 0.3)
    }

    func scrollViewDidEndScrollingAnimation(_ scrollView: UIScrollView) {


        // YOUR CODE ........
        NSObject.cancelPreviousPerformRequests(withTarget: self)
    }