我正在使用 Swift 编写以下代码。这是用于水平滚动的，可以很容易地适应垂直滚动。根据是否启用分页，解决方案会有所不同。两者都在下面给出。
class ScrollViewDelegate : NSObject, UIScrollViewDelegate
{
let maxOffset: CGFloat // offset of the rightmost content (scrollview contentSize.width - frame.width)
var prevOffset: CGFloat = 0 // previous offset (after adjusting the value)
var totalDistance: CGFloat = 0 // total distance it would have moved (had we not restricted)
let reductionFactor: CGFloat = 0.2 // percent of total distance it will be allowed to move (under restriction)
let scaleFactor: CGFloat = UIScreen.mainScreen().scale // pixels per point, for smooth translation in respective devices
init(maxOffset: CGFloat)
{
self.maxOffset = maxOffset // scrollView.contentSize.width - scrollView.frame.size.width
}
func scrollViewDidScroll(scrollView: UIScrollView)
{
let flipped = scrollView.contentOffset.x >= maxOffset // dealing with left edge or right edge rubber band
let currentOffset = flipped ? maxOffset - scrollView.contentOffset.x : scrollView.contentOffset.x // for right edge, flip the values as if screen is folded in half towards the left
if(currentOffset <= 0) // if dragging/moving beyond the edge
{
if(currentOffset <= prevOffset) // if dragging/moving beyond previous offset
{
totalDistance += currentOffset - prevOffset // add the "proposed delta" move to total distance
prevOffset = round(scaleFactor * totalDistance * reductionFactor) / scaleFactor // set the prevOffset to fraction of total distance
scrollView.contentOffset.x = flipped ? maxOffset - prevOffset : prevOffset // set the target offset, after negating any flipping
}
else // if dragging/moving is reversed, though still beyond the edge
{
totalDistance = currentOffset / reductionFactor // set totalDistance from offset (reverse of prevOffset calculation above)
prevOffset = currentOffset // set prevOffset
}
}
else // if dragging/moving inside the edge
{
totalDistance = 0 // reset the values
prevOffset = 0
}
}
}
启用分页后，返回到静止点的弹回似乎无法按预期工作。橡皮筋不是停在页面边界，而是越过它并停在非页面偏移处。如果从边缘拉动是快速轻弹，即使在您抬起手指之后，它也会继续朝那个方向移动，然后再反转方向并回到静止点，就会发生这种情况。如果您只是暂停并离开，甚至将其轻弹回静止点，它似乎工作正常。为了解决这个问题，在下面的代码中，我尝试识别超调的可能性，并在它返回并尝试越过预期的页面边界时强制停止它。
class PageScrollViewDelegate : NSObject, UIScrollViewDelegate
{
let maxOffset: CGFloat // offset of the rightmost content (scrollview contentSize.width - frame.width)
var prevOffset: CGFloat = 0 // previous offset (after adjusting the value)
var totalDistance: CGFloat = 0 // total distance it would have moved (had we not restricted)
let reductionFactor: CGFloat = 0.2 // percent of total distance it will be allowed to move (under restriction)
let scaleFactor: CGFloat = UIScreen.mainScreen().scale // pixels per point, for smooth translation in respective devices
var draggingOver: Bool = false // finger dragging is over or not
var overshoot: Bool = false // is there a chance for page to overshoot page boundary while falling back
init(maxOffset: CGFloat)
{
self.maxOffset = maxOffset // scrollView.contentSize.width - scrollView.frame.size.width
}
func scrollViewWillBeginDragging(scrollView: UIScrollView)
{
draggingOver = false // reset the flags
overshoot = false
}
func scrollViewDidEndDragging(scrollView: UIScrollView, willDecelerate decelerate: Bool)
{
draggingOver = true // finger dragging is over
}
func scrollViewDidScroll(scrollView: UIScrollView)
{
let flipped = scrollView.contentOffset.x >= 0.5 * maxOffset // dealing with left edge or right edge rubber band
let currentOffset = flipped ? maxOffset - scrollView.contentOffset.x : scrollView.contentOffset.x // for right edge, flip the values as if screen is folded in half towards the left
if(currentOffset <= 0) // if dragging/moving beyond the edge
{
if(currentOffset <= prevOffset) // if dragging/moving beyond previous offset
{
overshoot = draggingOver // is content moving farther away even after dragging is over (caused by fast flick, which can cause overshooting page boundary while falling back)
totalDistance += currentOffset - prevOffset // add the "proposed delta" move to total distance
prevOffset = round(scaleFactor * totalDistance * reductionFactor) / scaleFactor // set the prevOffset to fraction of total distance
scrollView.contentOffset.x = flipped ? maxOffset - prevOffset : prevOffset // set the target offset, after negating any flipping
}
else // if dragging/moving is reversed, though still beyond the edge
{
totalDistance = currentOffset / reductionFactor // set totalDistance from offset (reverse of prevOffset calculation above)
prevOffset = currentOffset // set prevOffset
}
}
else // if dragging/moving inside the edge
{
if(overshoot) // if this movement is a result of overshooting
{
scrollView.setContentOffset(CGPointMake(flipped ? maxOffset : 0, scrollView.contentOffset.y), animated: false) // bring it to resting point and stop further scrolling (this is a patch to control overshooting)
}
totalDistance = 0 // reset the values
prevOffset = 0
}
}
}