I see others questions on StackOverflow saying that i need to make sure that the paging is set to off. But I have done this and still it is not called.
Is there any thing i am missing?
Here is the sample project on Github. There is no code in it at all except the code to setup a collection view.
here is the code:
func collectionView(collectionView: UICollectionView, targetContentOffsetForProposedContentOffset proposedContentOffset: CGPoint) -> CGPoint {
return proposedContentOffset
}
As stated in Apple docs,
The proposed point (in the coordinate space of the collection view’s content view) for the upper-left corner of the visible content. This represents the point that the collection view has calculated as the most likely value to use for the animations or layout update.
In other words, it's called when you delete or insert cells to collection view.
You might be thinking of targetContentOffset(forProposedContentOffset:withScrollingVelocity:)
override func targetContentOffset(forProposedContentOffset proposedContentOffset: CGPoint, withScrollingVelocity velocity: CGPoint) -> CGPoint {
var contentOffset = proposedContentOffset
// do something with contentOffset
return contentOffset
}
with isPagingEnabled set to false on the collection view.
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)")
}
I have a view and within an image that works as a button. I would like to know if there is a way to lock the size of the button so that when I zoom in, the view remains small and does not enlarge with the view..
I thought it was hard to manager in the beginning. But finally, if you put the imageView in a UIScrollView, It's not hard to achieve.
The idea is move the buttonView outside of imageView during zooming and when zoom is over, put it back to imageView to pretend nothing happened. I know it's too verbose in programming but actually it works perfectly for your case.
var originalCenter : CGPoint! // The center of ButtonView in imageView.
//All functions are from the UIScrollViewDelegate.
func viewForZooming(in scrollView: UIScrollView) -> UIView?{
originalCenter = buttonView.center // remember the original position.
return imageView
}
func scrollViewWillBeginZooming(_ scrollView: UIScrollView, with view: UIView?) {
buttonView.frame = imageView.convert(buttonView.frame, to: scrollView)
scrollView.addSubview(buttonView)//add to superView of imageImage.
}
func scrollViewDidZoom(_ scrollView: UIScrollView){
buttonView.center = imageView.convert(originalCenter, to: scrollView) //During Zooming, update the buttonView in ScrollView.
}
func scrollViewDidEndZooming(_ scrollView: UIScrollView, with view: UIView?, atScale scale: CGFloat){
buttonView.frame = imageView.convert(buttonView.frame, from: scrollView)
imageView.addSubview(buttonView) //put it back.
}
I know it's better to use a parameter to control such operation. But I have-not found one according to public APIs. Maybe there is a better way, hope this one is your answer too.
Because you called transform for superView. It will make all subViews inside transform together.
You need to remake you views:
SuperView:
- Content view (the image view)
- Border view
- Button close
When you want to zoom the image, you only need to reset the superview frame.
You found a git SPUserResizableView.
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
I have a layout with a UIView at the top of the page and, right below it, I have a UITableView.
What I am wanting to do is to transfer the gesture interactions on the UIView to the UITableView, so when the user makes a drag up/down on the UIView, the UITableView scrolls vertically.
I tried the following code
tableView.gestureRecognizers?.forEach { uiView.addGestureRecognizer($0) }
but it removed the gestureRecognizers from the UITableView somehow :/
Obs.: the UIView cannot be a Header of the UIScrollView
That's Tricky
What is problem ?
Your top view is not allowed to pass through view behind it...
What would be possible solutions
pass all touches to view behind it (Seems to not possible or very tough practically )
Tell window to ignore touches on top view (Easy one)
Second option is better and easy.
So What you need to do is create subclass of UIView and override
override func hitTest(_ point: CGPoint, with event: UIEvent?) -> UIView?
and return nil if you found same view on hitTest action
Here Tested and working example
class PassThroughME : UIView {
override func hitTest(_ point: CGPoint, with event: UIEvent?) -> UIView? {
return super.hitTest(point, with: event) == self ? nil : self
}
}
That's it now use PassThroughME either by adding class to your view in storyboard or programmatically whatever way you have added your view
Check image i have black color view with 0.7 alpha on top still i am able to scroll
Hope it is helpful
I'd like to call or not call a method depending on how fast user has scrolled.
It has to be instantly measured as user's finger goes because the method needs to be either called or ignored the second it starts moving, not when it has stopped.
This works for me.
CGPoint scrollVelocity = [[self.tableView panGestureRecognizer] velocityInView:self.tableView];
NSLog(#"scroll velocity : %f",scrollVelocity.y);
This method exposes the velocity value. It is part of the scroll view delegate.
optional func scrollViewWillEndDragging(_ scrollView: UIScrollView,
withVelocity velocity: CGPoint,
targetContentOffset: UnsafeMutablePointer<CGPoint>){
}