Something special has to be done to animate a constraint instantiated programmatically?
I instantiate a constraint programmatically as a lazy variable:
private lazy var topConstraint: NSLayoutConstraint = {
let constraint = view.topAnchor.constraint(equalTo: otherView.topAnchor, constant: otherView)
return constraint
}()
Then, I animate a change in the constant of this constraint:
topConstraint.constant = newValue
view.setNeedsLayout()
UIView.animate(withDuration: 1) {
self.view.layoutIfNeeded()
}
It is not working... I also have tried putting the constant setting into the block:
UIView.animate(withDuration: 1) {
self.topConstraint.constant = newValue
self.view.setNeedsLayout()
self.view.layoutIfNeeded()
}
But I achieved nothing at all, I've tried almost all the combinations. The constraint constant is properly changed, but always without animation.
PD: I also gave a shot to UIViewPropertyAnimator.
No need for setNeedsLayout().
self.topConstraint.constant = 0.0
UIView.animate(withDuration: 1.0) {[weak self] in
self?.topConstraint.constant = 10.0
self?.view.layoutIfNeeded()
}
I have UITableView on the left size and plain UIView on the right side in my UIViewController
UITableView connects to .top, .leading and .bottom of
superview
UIView connects to .top, .trailing and .bottom of
superview, also it has .width
And UITableView .leading ==
.trailing of UIView
All these constraints you can see on the screenshot:
Here is my animation code in the controller, as you can see I update .width of UIView and also I cycle the animation.
class ViewController: UIViewController {
#IBOutlet var widthConstaint: NSLayoutConstraint!
#IBOutlet var tableView: UITableView!
#IBOutlet var watchContainerView: UIView!
override func viewDidLoad() {
super.viewDidLoad()
start()
}
func start() {
DispatchQueue.main.asyncAfter(deadline: .now() + 3) {
if self.widthConstaint.constant == 50 {
self.change(width: 100)
} else {
self.change(width: 50)
}
self.start()
}
}
func change(width: CGFloat) {
widthConstaint.constant = width
UIView.animate(withDuration: 1.0) {
self.view.layoutIfNeeded()
}
}
}
extension ViewController: UITableViewDataSource {
func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
let cell = tableView.dequeueReusableCell(withIdentifier: "Cell", for: indexPath)
return cell
}
func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
return 300
}
}
As a result you can see this on .gif, what I should for smooth animation, without this glitch?
UPDATE
I tried to reproduce the UILabel wrong behavior with my own UIView subclass:
class MyView: UIView {
var currentSize: CGSize = .zero
override func layoutSubviews() {
super.layoutSubviews()
guard currentSize != bounds.size else { return }
currentSize = bounds.size
setNeedsDisplay()
}
override func draw(_ rect: CGRect) {
UIColor.purple.setFill()
UIBezierPath(rect: rect).fill()
let square = CGRect(x: rect.width - 50, y: rect.origin.y, width: 50, height: rect.height)
UIColor.blue.setFill()
UIBezierPath(rect: square).fill()
}
}
The view draws a little blue rectangle at its right, as a text. And… well… the animation is also good!
But if I change the contentMode to left (the default value is scaleToFill):
The blue square jumps from one place to the other.
So, I found out this is not only related to the UILabel's textAlignment. It's its combinaison with the default left content mode of the UILabel.
contentMode defines how the content should be adjusted if the content's size and the bounds size are different - this is case during the animation, the view redraws itself with its new size right before being resized.
So
label.contentMode = .left // default
label.textAlignment = .left
will behave as:
label.contentMode = .right
label.textAlignment = .right
PREVIOUS ANSWER
I spent some time on your problem. Guess what?
It's not related to the table view at all. It's because of the .right text alignment of the label.
You can reproduce the glitch with a simple UILabel:
class ViewController: UIViewController {
let label = UILabel()
var rightConstraint: NSLayoutConstraint!
override func loadView() {
view = UIView()
view.backgroundColor = .white
}
override func viewDidLoad() {
super.viewDidLoad()
setUpView()
start()
}
func start() {
DispatchQueue.main.asyncAfter(deadline: .now() + 3) {
if self.rightConstraint.constant == 50 {
self.change(width: 100)
} else {
self.change(width: 50)
}
self.start()
}
}
func change(width: CGFloat) {
rightConstraint.constant = width
UIView.animate(withDuration: 1.0) {
self.view.layoutIfNeeded()
}
}
func setUpView() {
label.text = "Label"
label.textAlignment = .right
view.addSubview(label)
label.translatesAutoresizingMaskIntoConstraints = false
rightConstraint = view.trailingAnchor.constraint(equalTo: label.trailingAnchor)
rightConstraint.isActive = true
label.leadingAnchor.constraint(equalTo: view.leadingAnchor).isActive = true
label.topAnchor.constraint(equalTo: view.topAnchor).isActive = true
label.bottomAnchor.constraint(equalTo: view.bottomAnchor).isActive = true
label.topAnchor.constraint(equalTo: view.topAnchor).isActive = true
}
}
Why?
To find out the error, I created a UILabel subclass and overrode action(for: CALayer, forKey: String). It's where each UIView decides which animation to apply in response to a property change (ref). I was looking for some weird animation behaviors when a label is inside a table view.
If you print key, you'd see that actions are requested for the position, the bounds and the contents of the label when UIKit is about to commit the animations related to your UIView.animate(withDuration:) call.
In fact, setNeedsDisplay is called each time the size of an UILabel is changed (it makes sens). So I guess there is a conflict between the content redrawing of the label and its frame change.
I think you should recreate the right text alignment of the label without using textAlignment = .right.
Horizontally, pin the label to the right only. When layoutIfNeeded will be called, only the label's position will change, not its content.
As mentioned in the #Gaétanz answer. The abnormal behaviour is due to the Lable inside the cell.
You can remove the glitches by changing the Labels leading constraint relation to >= and change the priority to 999 from 1000.
Please refer the screenshot attached for your reference.
When you add constraint with a priority less than 1000 it will be an optional constraint. Priority 1000 is the required priority for a constraint. Here if you added a priority of 999, all the other constraints with priority 1000 will layout first and the less priority constraint will layout last.
You are changing the width of your side view outside of the animation block. put you widthConstaint.constant = width inside your animation block.
func change(width: CGFloat) {
UIView.animate(withDuration: 1.0) {
self.widthConstaint.constant = width
self.view.layoutIfNeeded()
}
}
According to your code the View is animated but the constraint is not put in the UIView animation block. So it looks like a glitch cause it changes the frame directly. Please try to change the code as below and try.
func change(width: CGFloat) {
UIView.animate(withDuration: 1.0) {
widthConstaint.constant = width
self.tableView.layoutIfNeeded()
self.view.layoutIfNeeded()
}
}
I made an UIScrollView in a XIB for my onboarding. The UIScrollView has 3 onboarding views. Long story short:
This works perfect. However I want the top left and right buttons (Overslaan - Volgende) to animate up / off the screen when the third/last page is on screen. My UIScrollView starts behaving weird when I animate the buttons off:
This is the code im using:
func scrollViewWillEndDragging(_ scrollView: UIScrollView, withVelocity velocity: CGPoint, targetContentOffset: UnsafeMutablePointer<CGPoint>) {
let pageIndex = Int(targetContentOffset.pointee.x / self.frame.width)
pageControl.currentPage = pageIndex
if stepViews[pageIndex] is OnboardingLoginView {
moveControlConstraintsOffScreen()
} else {
moveControlConstraintsOnScreen()
}
UIView.animate(withDuration: 0.5, delay: 0, usingSpringWithDamping: 1, initialSpringVelocity: 1, options: .curveEaseOut, animations: {
self.layoutIfNeeded()
}, completion: nil)
}
I debugged the code and it turns out that setting a new constant for the constraints causes the issue, regardless of the animation block. How do I make the buttons move up/off the screen without my scrollView behaving weird?
It looks like triggering a layout pass is interfering with your scroll view positioning. You could implement func scrollViewDidScroll(_ scrollView: UIScrollView) and try to update the button view on a per-frame basis, without changing Auto Layout constraints. I usually use the transform property for frame changes outside of Auto Layout, since any changes to frame or bounds are overwritten during the next layout pass.
func scrollViewDidScroll(_ scrollView: UIScrollView) {
guard mustBeOnLastPage else {
buttonOne.tranform = .identity
buttonTwo.tranform = .identity
return
}
let offset = scrollView.contentOffset.x
buttonOne.tranform = .init(translationX: 0, y: offset)
buttonTwo.tranform = .init(translationX: 0, y: offset)
}
Old answer
This interpretation is a bit of tangent of what you're asking for.
Since it looks like you're using the scroll view in a paging context, I would approach this problem by using UIPageViewController. Since UIPageViewController uses UIScrollView internally, you can observe the contentOffset of the last view in the scroll view to determine how far along the page has scrolled.
Yes, this involves looking inside the view hierarchy, but Apple hasn't changed it for half a decade so you should be safe. Coincidentally, I actually implemented this approach last week and it works like a charm.
If you're interested, I can further expand on this topic. The post that pointed me in the right direction can be found here.
Here is what i do
I can't post image，you can look at this http://i.imgur.com/U7FHoMu.gif
and this is the code
var centerYConstraint: Constraint!
func setupConstraint() {
fadeView.snp.makeConstraints { make in
make.centerX.equalToSuperview()
centerYConstraint = make.centerY.equalToSuperview().constraint
make.size.equalTo(CGSize(width: 50, height: 50))
}
}
func scrollViewWillEndDragging(_ scrollView: UIScrollView, withVelocity velocity: CGPoint,targetContentOffset: UnsafeMutablePointer<CGPoint>) {
let pageIndex = Int(targetContentOffset.pointee.x / self.view.frame.width)
if pageIndex != 1 {
centerYConstraint.update(offset: self.view.frame.height)
} else {
centerYConstraint.update(offset: 0)
}
UIView.animate(withDuration: 0.5, delay: 0, usingSpringWithDamping: 1, initialSpringVelocity: 1, options: .curveEaseOut, animations: {
self.view.layoutIfNeeded()
}, completion: nil)
}
Based on #CloakedEddy's answer I made 2 changes:
1: It seems layoutSubviews is responsible for the weird behaviour. To fix this I prevent the scrollView from calling layoutSubviews all the time:
override func layoutSubviews() {
super.layoutSubviews()
if !didLayoutSubviews {
for index in 0..<stepViews.count {
let page: UIView = stepViews[index]
let xPosition = scrollView.frame.width * CGFloat(index)
page.frame = CGRect(x: xPosition, y: 0, width: scrollView.bounds.width, height: scrollView.frame.height)
scrollView.contentSize.width = scrollView.frame.width * CGFloat(index + 1)
}
didLayoutSubviews = true
}
}
2: If you want to update your views for device orientations:
override func viewWillTransition(to size: CGSize, with coordinator: UIViewControllerTransitionCoordinator) {
super.viewWillTransition(to: size, with: coordinator)
onboardingView.didLayoutSubviews = false
onboardingView.setNeedsLayout()
}
I have a few screens worth of content within my UIScrollView which only scrolls vertically.
I want to programmatically scroll to a view contained somewhere in it's hierarchy.
The UIScrollView move so that the child view is at the top of the UIScrollView (either animated or not)
Here's an extension I ended up writing.
Usage:
Called from my viewController, self.scrollView is an outlet to the UIScrollView and self.commentsHeader is a view within it, near the bottom:
self.scrollView.scrollToView(self.commentsHeader, animated: true)
Code:
You only need the scrollToView method, but leaving in scrollToBottom / scrollToTop methods too as you'll probably need those too, but feel free to delete them.
extension UIScrollView {
// Scroll to a specific view so that it's top is at the top our scrollview
func scrollToView(view:UIView, animated: Bool) {
if let origin = view.superview {
// Get the Y position of your child view
let childStartPoint = origin.convertPoint(view.frame.origin, toView: self)
// Scroll to a rectangle starting at the Y of your subview, with a height of the scrollview
self.scrollRectToVisible(CGRect(x:0, y:childStartPoint.y,width: 1,height: self.frame.height), animated: animated)
}
}
// Bonus: Scroll to top
func scrollToTop(animated: Bool) {
let topOffset = CGPoint(x: 0, y: -contentInset.top)
setContentOffset(topOffset, animated: animated)
}
// Bonus: Scroll to bottom
func scrollToBottom() {
let bottomOffset = CGPoint(x: 0, y: contentSize.height - bounds.size.height + contentInset.bottom)
if(bottomOffset.y > 0) {
setContentOffset(bottomOffset, animated: true)
}
}
}
scrollView.scrollRectToVisible(CGRect(x: x, y: y, width: 1, height:
1), animated: true)
or
scrollView.setContentOffset(CGPoint(x: x, y: y), animated: true)
Another way is
scrollView.contentOffset = CGPointMake(x,y);
and i do it with animated like this
[UIView animateWithDuration:2.0f delay:0 options:UIViewAnimationOptionCurveLinear animations:^{
scrollView.contentOffset = CGPointMake(x, y); }
completion:NULL];
scrollView.setContentOffset(CGPoint, animated: Bool)
Where the point's y coordinate is the y coordinate of the frame of the view you want to show relatively to the scrollView's content view.
Here is my answer, this is in swift. This will scroll the pages in scrollview infinitely.
private func startBannerSlideShow()
{
UIView.animate(withDuration: 6, delay: 0.1, options: .allowUserInteraction, animations: {
scrollviewOutlt.contentOffset.x = (scrollviewOutlt.contentOffset.x == scrollviewOutlt.bounds.width*2) ? 0 : scrollviewOutlt.contentOffset.x+scrollviewOutlt.bounds.width
}, completion: { (status) in
self.startBannerSlideShow()
})
}
Updated dyson's answer to behave like UITableView's scrollToRowAtIndexPath:atScrollPosition:animated: since that was my use case:
extension UIScrollView {
/// Scrolls to a subview of the current `UIScrollView `.
/// - Parameters:
/// - view: The subview to which it should scroll to.
/// - position: A constant that identifies a relative position in the `UIScrollView ` (top, middle, bottom) for the subview when scrolling concludes. See UITableViewScrollPosition for descriptions of valid constants.
/// - animated: `true` if you want to animate the change in position; `false` if it should be immediate.
func scrollToView(view: UIView,
position: UITableView.ScrollPosition = .top,
animated: Bool) {
// Position 'None' should not scroll view to top if visible like in UITableView
if position == .none &&
bounds.intersects(view.frame) {
return
}
if let origin = view.superview {
// Get the subview's start point relative to the current UIScrollView
let childStartPoint = origin.convert(view.frame.origin,
to: self)
var scrollPointY: CGFloat
switch position {
case .bottom:
let childEndY = childStartPoint.y + view.frame.height
scrollPointY = CGFloat.maximum(childEndY - frame.size.height, 0)
case .middle:
let childCenterY = childStartPoint.y + view.frame.height / 2.0
let scrollViewCenterY = frame.size.height / 2.0
scrollPointY = CGFloat.maximum(childCenterY - scrollViewCenterY, 0)
default:
// Scroll to top
scrollPointY = childStartPoint.y
}
// Scroll to the calculated Y point
scrollRectToVisible(CGRect(x: 0,
y: scrollPointY,
width: 1,
height: frame.height),
animated: animated)
}
}
/// Scrolls to the top of the current `UIScrollView`.
/// - Parameter animated: `true` if you want to animate the change in position; `false` if it should be immediate.
func scrollToTop(animated: Bool) {
let topOffset = CGPoint(x: 0, y: -contentInset.top)
setContentOffset(topOffset, animated: animated)
}
/// Scrolls to the bottom of the current `UIScrollView`.
/// - Parameter animated: `true` if you want to animate the change in position; `false` if it should be immediate.
func scrollToBottom(animated: Bool) {
let bottomOffset = CGPoint(x: 0,
y: contentSize.height - bounds.size.height + contentInset.bottom)
if (bottomOffset.y > 0) {
setContentOffset(bottomOffset, animated: animated)
}
}
}
swift 5.0 code
extension UIScrollView {
// Scroll to a specific view so that it's top is at the top our scrollview
func scrollToView(view:UIView, animated: Bool) {
if let origin = view.superview {
// Get the Y position of your child view
let childStartPoint = origin.convert(view.frame.origin, to: self)
// Scroll to a rectangle starting at the Y of your subview, with a height of the scrollview
self.scrollRectToVisible(CGRect(x:0, y:childStartPoint.y,width: 1,height: self.frame.height), animated: animated)
}
}
// Bonus: Scroll to top
func scrollToTop(animated: Bool) {
let topOffset = CGPoint(x: 0, y: -contentInset.top)
setContentOffset(topOffset, animated: animated)
}
// Bonus: Scroll to bottom
func scrollToBottom() {
let bottomOffset = CGPoint(x: 0, y: contentSize.height - bounds.size.height + contentInset.bottom)
if(bottomOffset.y > 0) {
setContentOffset(bottomOffset, animated: true)
}
}
}
For me, the thing was the navigation bar which overlapped the small portion of the scrollView content. So I've made 2 things:
Size Inspector - Scroll View - Content Insets --> Change from Automatic to Never.
Size Inspector - Constraints- "Align Top to" (Top Alignment Constraints)- Second item --> Change from Superview.Top to Safe Area.Top and the value(constant field) set to 0
For me scrollRectToVisible() didn't work (see here), so I used setContentOffset() and calculated it myself, based on AMAN77's answer:
extension UIScrollView {
func scrollToView(view:UIView, animated: Bool) {
if let superview = view.superview {
let child = superview.convert(view.frame, to: self)
let visible = CGRect(origin: contentOffset, size: visibleSize)
let newOffsetY = child.minY < visible.minY ? child.minY : child.maxY > visible.maxY ? child.maxY - visible.height : nil
if let y = newOffsetY {
setContentOffset(CGPoint(x:0, y: y), animated: animated)
}
}
}
}
It is for a horizontal scroll view, but the same idea can be applied vertically too.
For scroll to top or bottom with completion of the animation
// MARK: - UIScrollView extensions
extension UIScrollView {
/// Animate scroll to bottom with completion
///
/// - Parameters:
/// - duration: TimeInterval
/// - completion: Completion block
func animateScrollToBottom(withDuration duration: TimeInterval,
completion: (()->())? = nil) {
UIView.animate(withDuration: duration, animations: { [weak self] in
self?.setContentOffset(CGPoint.zero, animated: false)
}, completion: { finish in
if finish { completion?() }
})
}
/// Animate scroll to top with completion
///
/// - Parameters:
/// - duration: TimeInterval
/// - completion: Completion block
func animateScrollToBottomTop(withDuration duration: TimeInterval,
completion: (()->())? = nil) {
UIView.animate(withDuration: duration, animations: { [weak self] in
guard let `self` = self else {
return
}
let desiredOffset = CGPoint(x: 0, y: -self.contentInset.top)
self.setContentOffset(desiredOffset, animated: false)
}, completion: { finish in
if finish { completion?() }
})
}
}
It is important to point out for any of you beginners out there that you will need to link the UIScrollView from your story board into you code then use the extension ".nameoffunction"
For example:
you import your UIScrollView to your code and name it bob.
you have an extension script written like the one above by "dyson returns"
you now write in your code:
"bob.scrollToTop"
This attached the extension function "scrollToTop" to you UIScrollView in the storyboard.
Good luck and chin up!
You can use the following method , it works well for me
func scrollViewToTop( _ someView:UIView)
{
let targetViewTop = someView.frame.origin.y
//If you have a complicated hierarchy it is better to
// use someView superview (someView.superview?.frame.origin.y) and figure out your view origin
let viewToTop = targetViewTop - scrollView.contentInset.top
scrollView.setContentOffset(CGPoint(x: 0, y: viewToTop), animated: true)
}
Or you can have as an extension
extension UIScrollView
{
func scrollViewToTop( _ someView:UIView){
let targetViewTop = someView.frame.origin.y
let viewToTop = targetViewTop - self.contentInset.top
self.setContentOffset(CGPoint(x: 0, y: viewToTop), animated: true)
}
}
here are constraints for the scroll view
some screen shots
Screen Shots2
I have view sView inside my ViewController. It height has constraint - I created IBOutlet for this constraint - sViewHeightConstraint. I want to decrease height of sView with animation.
I created function
UIView.animateWithDuration(5.5, animations: {
self.sViewHeightConstraint.constant = 50
})
Height of view is changing but i don't see any animation. What I am doing wrong?
use layoutIfNeeded()
view.layoutIfNeeded() // force any pending operations to finish
UIView.animateWithDuration(0.2, animations: { () -> Void in
self.sViewHeightConstraint.constant = 50
self.view.layoutIfNeeded()
})
swift 3
view.layoutIfNeeded()
sViewHeightConstraint.constant = 50
UIView.animate(withDuration: 1.0, animations: {
self.view.layoutIfNeeded()
})
In case your view updates but animation isn't working, this solution works for me.
UIView.animate(withDuration: 0.2, animations: {
self.sViewHeightConstraint.constant = 50
self.sView.size = CGSize(width: self.sView.frame.width, height: 50)
self.view.layoutIfNeeded()
})