I have a list of cells of varying height, and I want the scroll to top perfectly at the top of a cell.
For this I can use
func scrollViewWillEndDragging(_ scrollView: UIScrollView, withVelocity velocity: CGPoint, targetContentOffset: UnsafeMutablePointer<CGPoint>) {
And I can set the targetContentOffset to the top of a cells frame.
However if cells yet to be laid out have a height different from their estimated height, then this destination cells origin will change, and I don't get a chance to account for this.
Is there anyway to land perfectly on a cell after a scroll when the origin can change?
Related
I’m trying to implement a custom top bar that behaves similarly to the iOS 11+ large title navigation bar, where the large title section of the bar collapses when scrolling down the content:
The difference is that my bar needs a custom height and also a bottom section that doesn’t collapse when scrolled. I managed to get that part working:
The bar is implemented using a UIStackView & with some non-required layout constraints, but I believe its internal implementation is not relevant. The most important thing is that the height of the bar is tied to scrollview's top contentInset. These are driven by scrollview's contentOffset in UIScrollViewDelegate.scrollViewDidScroll method:
func scrollViewDidScroll(_ scrollView: UIScrollView) {
let topInset = (-scrollView.contentOffset.y).limitedBy(topBarHeightRange)
// changes both contentInset and scrollIndicatorInsets
adjustTopContentInset(topInset)
// changes top bar height
heightConstraint?.constant = topInset
adjustSmallTitleAlpha()
}
topBarHeightRange stores the minimum and maximum bar height
One thing that I'm having a problem with is that when the user stops scrolling the scrollview, it's possible that the bar will end up in a semi-collapsed state. Again, let's look at the desired behavior:
Content offset is snapped to either the compact or expanded height, whichever is "closer". I'm trying to achieve the same in UIScrollViewDelegate.scrollViewWillEndDragging method:
func scrollViewWillEndDragging(_ scrollView: UIScrollView,
withVelocity velocity: CGPoint,
targetContentOffset: UnsafeMutablePointer<CGPoint>) {
let targetY = targetContentOffset.pointee.y
// snaps to a "closer" value
let snappedTargetY = targetY.snappedTo([topBarHeightRange.lowerBound, topBarHeightRange.upperBound].map(-))
targetContentOffset.pointee.y = snappedTargetY
print("Snapped: \(targetY) -> \(snappedTargetY)")
}
The effect is far from perfect:
When I look at the printout it shows that the targetContentOffset is modified correctly. However, visually in the app the content offset is snapped only to the compact height but not to the expanded height (you can observe that the large "Title" label ends up being cut in half instead of back to the "expanded" position.
I suspect this issue has something to do with changing the contentInset.top while the user is scrolling, but I can't figure out how to fix this behavior.
It's a bit hard to explain the problem, so I hope the GIFs help. Here's the repo: https://github.com/AleksanderMaj/ScrollView
Any ideas how to make the scrollview/bar combo snap to compact/expanded height properly?
I took a look at your project and liked your implementation.
I came up with a solution in your scrollViewWillEndDragging method by adding the following code at the end of method:
if abs(targetY) < abs(snappedTargetY) {
scrollView.setContentOffset(CGPoint(x: 0, y: snappedTargetY), animated: true)
}
Basically, if the scroll down amount is not worth hiding the large title (it happens if targetY is less than snappedTargetY) then just scroll to value of snappedTargetY to show the large title back.
Seems to be working for now, but let me know if you encounter any bugs or find a way to improve.
Whole scrollViewWillEndDragging method:
func scrollViewWillEndDragging(_ scrollView: UIScrollView,
withVelocity velocity: CGPoint,
targetContentOffset: UnsafeMutablePointer<CGPoint>) {
let targetY = targetContentOffset.pointee.y
// snaps to a "closer" value
let snappedTargetY = targetY.snappedTo([topBarHeightRange.lowerBound, topBarHeightRange.upperBound].map(-))
targetContentOffset.pointee.y = snappedTargetY
if abs(targetY) < abs(snappedTargetY) {
scrollView.setContentOffset(CGPoint(x: 0, y: snappedTargetY), animated: true)
}
print("Snapped: \(targetY) -> \(snappedTargetY)")
}
In my UIViewController I have a UICollectionView. The delegate is set properly. It just works fine. isPagingEnabled is set to true. But now I want to change the paging-positions I tried it within scrollViewWillEndDragging, because in the documentation it says:
Your application can change the value of the targetContentOffset parameter to adjust where the scrollview finishes its scrolling animation.
This functions is called properly but the only thing happens when I want to set a new Endpoint, the UICollectionView scrolls to 0.
This is my code:
func scrollViewWillEndDragging(_ scrollView: UIScrollView, withVelocity velocity: CGPoint, targetContentOffset: UnsafeMutablePointer<CGPoint>) {
print(scrollView.contentOffset, "actual Offset")
print(targetContentOffset.pointee, "future offset")
targetContentOffset.pointee = CGPoint(x: 100, y: 0)
print(targetContentOffset.pointee, "new future offset")
}
At the print("new future offset"), it prints the right value. So it seems the value is mutated after this function.
func targetContentOffset(forProposedContentOffset proposedContentOffset: CGPoint,
withScrollingVelocity velocity: CGPoint) -> CGPoint
Description:
If you want the scrolling behavior to snap to specific boundaries, you
can override this method and use it to change the point at which to
stop. For example, you might use this method to always stop scrolling
on a boundary between items, as opposed to stopping in the middle of
an item.
Override this layout method instead of directly changing value of targetContentOffset.
If you want the scrolling behavior to snap to specific boundaries, you can override this method and use it to change the point at which to stop. For example, you might use this method to always stop scrolling on a boundary between items, as opposed to stopping in the middle of an item.
Docs:
https://developer.apple.com/documentation/uikit/uicollectionviewlayout/1617729-targetcontentoffset
Currently tableview cells look like this: current cell image When my app first opens it looks like the picture on the left and when I scroll one page down it looks like the picture on the right.
However I want it to look like a carousel: like this
I want it so when it I scroll (paging enabled) the bottom cell comes to middle cell spot, and the new bottom cell is at the old bottom cell spot, and the middle cell is at the top cell spot.
Possible Solutions/Questions:
How would I make the UITableViewCells infinitely loop, and thus start off with the ability to scroll up and down, since the last cell would be above the first cell to begin with. Right now there is no cell above the first one, which poses a problem.
CODE:
func scrollViewWillEndDragging(_ scrollView: UIScrollView, withVelocity velocity: CGPoint, targetContentOffset: UnsafeMutablePointer<CGPoint>) {
targetContentOffset.pointee.y = self.tableView.contentOffset.y + 100
}
I want to basically snap the bottom card/ top card that is swiping to the middle of the screen.
Can anybody help me please?:)
How can I set constraints in a storyboard for Page Control Indicator so when I am listing my collectionView pages the indicator isn't moving.
I've tried setting constraints for page control indicator, but there is just option to set it with cell frame. So when I list a collection view indicator appears again and again on each new page.
Screenshot:
You have to set the currentpage in the pageControl. The best is at the function scrollViewWillEndDragging:
override func scrollViewWillEndDragging(_ scrollView: UIScrollView, withVelocity velocity: CGPoint, targetContentOffset: UnsafeMutablePointer<CGPoint>) {
let pageNumber = Int(targetContentOffset.pointee.x / view.frame.width)
pageControl.currentPage = pageNumber
}
then it will work :)
Trying to set targetContentOffset in scrollview delegate method to snap tableView to desired position(top,middle,bottom),but after snap action the tableView decelerate to the position but its not finishing animation very fast it gets slow down after few seconds.i tried to change the speed by putting some lower number (0.97,0.96…..) but still its is same,I have also tried putting the same content in UIView animation block but there is no change in speed? How Can I speed up deceleration Rate more than UIScrollViewDecelerationRateFast?
tableView.decelerationRate = UIScrollViewDecelerationRateFast
var scrollRect:CGRect = scrollView.frame;
func scrollViewWillEndDragging(scrollView: UIScrollView, withVelocity velocity: CGPoint, targetContentOffset: UnsafeMutablePointer<CGPoint>) {
scrollRect.origin.y = self.getNextPosition(position, previousPosition: self.previousPosition, fastScroll: isFastScroll! , andScrollDirection: self.scrollDirection!,isFrameChanged:frameChanged)
targetContentOffset.memory.y = scrollRect.origin.y
}