How do I animate constraint changes

Question

I m updating an old app with an AdBannerView and when there is no ad  it slides off screen  When there is an ad it slides on the screen  Basic stuff   Old style  I set the frame in an animation block  New style  I have a IBOutlet to the auto-layout constraint which determines the Y position  in this case it s distance from the bottom of the superview  and modify the constant   -  void moveBannerOffScreen        UIView animateWithDuration 5 animations             addBannerDistanceFromBottomConstraint constant   -32              bannerIsVisible   FALSE     -  void moveBannerOnScreen        UIView animateWithDuration 5 animations             addBannerDistanceFromBottomConstraint constant   0              bannerIsVisible   TRUE      And the banner moves  exactly as expected  but no animation     UPDATE  I re-watched WWDC 12 talk Best Practices for Mastering Auto Layout which covers animation  It discusses how to update constraints using CoreAnimation       I ve tried with the following code  but get the exact same results   -  void moveBannerOffScreen        addBannerDistanceFromBottomConstraint constant   -32       UIView animateWithDuration 2 animations             self view setNeedsLayout               bannerIsVisible   FALSE     -  void moveBannerOnScreen        addBannerDistanceFromBottomConstraint constant   0       UIView animateWithDuration 2 animations             self view setNeedsLayout               bannerIsVisible   TRUE      On a side note  I have checked numerous times and this is being executed on the main thread

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Swift 4 solution  UIView animate  Three simple steps    Change the constraints  e g    heightAnchor constant   50  Tell the containing view that its layout is dirty and that the autolayout should recalculate the layout   self view setNeedsLayout    In animation block tell the layout to recalculate the layout  which is equivalent of setting the frames directly  in this case the autolayout will set the frames    UIView animate withDuration  0 5        self view layoutIfNeeded        Complete simplest example   heightAnchor constant   50 self view setNeedsLayout   UIView animate withDuration  0 5        self view layoutIfNeeded       Sidenote  There is an optional 0th step - before changing the constraints you might want to call self view layoutIfNeeded   to make sure that the starting point for the animation is from the state with old constraints applied  in case there were some other constraints changes that should not be included in animation    otherConstraint constant   30    this will make sure that otherConstraint won t be animated but will take effect immediately self view layoutIfNeeded    heightAnchor constant   50 self view setNeedsLayout   UIView animate withDuration  0 5        self view layoutIfNeeded       UIViewPropertyAnimator  Since with iOS 10 we got a new animating mechanism - UIViewPropertyAnimator  we should know that basically the same mechanism applies to it  The steps are basically the same   heightAnchor constant   50 self view setNeedsLayout   let animator   UIViewPropertyAnimator duration  0 5  timingParameters  UICubicTimingParameters animationCurve   linear   animator addAnimations       self view layoutIfNeeded     animator startAnimation     Since animator is an encapsulation of the animation  we can keep reference to it and call it later  However  since in the animation block we just tell the autolayout to recalculate the frames  we have to change the constraints before calling startAnimation  Therefore something like this is possible      prepare the animator first and keep a reference to it let animator   UIViewPropertyAnimator duration  0 5  timingParameters  UICubicTimingParameters animationCurve   linear   animator addAnimations       self view layoutIfNeeded         at some other point in time we change the constraints and call the animator heightAnchor constant   50 self view setNeedsLayout   animator startAnimation     The order of changing constraints and starting an animator is important - if we just change the constraints and leave our animator for some later point  the next redraw cycle can invoke autolayout recalculation and the change will not be animated   Also  remember that a single animator is non-reusable - once you run it  you cannot  rerun  it  So I guess there is not really a good reason to keep the animator around  unless we use it for controlling an interactive animation

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Generally  you just need to update constraints and call layoutIfNeeded inside the animation block  This can be either changing the  constant property of an NSLayoutConstraint  adding remove constraints  iOS 7   or changing the  active property of constraints  iOS 8  amp  9    Sample Code    UIView animateWithDuration 0 3 animations           Move to right     self leadingConstraint active   false      self trailingConstraint active   true          Move to bottom     self topConstraint active   false      self bottomConstraint active   true          Make the animation happen      self view setNeedsLayout        self view layoutIfNeeded         Sample Setup     Controversy  There are some questions about whether the constraint should be changed before the animation block  or inside it  see previous answers    The following is a Twitter conversation between Martin Pilkington who teaches iOS  and Ken Ferry who wrote Auto Layout  Ken explains that though changing constants outside of the animation block may currently work  it s not safe and they should really be change inside the animation block  https   twitter com kongtomorrow status 440627401018466305  Animation     Sample Project  Here s a simple project showing how a view can be animated  It s using Objective C and animates the view by changing the  active property of several constraints  https   github com shepting SampleAutoLayoutAnimation

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In the context of constraint animation  I would like to mention a specific situation where I animated a constraint immediately within a keyboard opened notification    Constraint defined a top space from a textfield to top of the container  Upon keyboard opening  I just divide the constant by 2   I was unable to achieve a conistent smooth constraint animation directly within the keyboard notification  About half the times view would just jump to its new position - without animating   It occured to me there might be some additional layouting happening as result of keyboard opening   Adding a simple dispatch after block with a 10ms delay made the animation run every time - no jumping

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There is an article talk about this  http   weblog invasivecode com post 42362079291 auto-layout-and-core-animation-auto-layout-was  In which  he coded like this   -  void handleTapFrom  UIGestureRecognizer   gesture       if   isVisible             isVisible   NO          self topConstraint constant   -44         1          self navbar setNeedsUpdateConstraints       2          UIView animateWithDuration  3 animations                 self navbar layoutIfNeeded      3                   else            isVisible   YES          self topConstraint constant   0            self navbar setNeedsUpdateConstraints            UIView animateWithDuration  3 animations                 self navbar layoutIfNeeded                         Hope it helps

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Swift solution   yourConstraint constant   50 UIView animate withDuration  1 0  animations        yourView layoutIfNeeded

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Step 1  update your constraint self myOutletToConstraint constant   50     New height  for example      Step 2  trigger animation  UIView animateWithDuration 2 0 animations            Step 3  call layoutIfNeeded on your animated view s parent      self view layoutIfNeeded

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Two important notes    You need to call layoutIfNeeded within the animation block   Apple actually recommends you call it once before the animation block to ensure that all pending layout operations have been completed   You need to call it specifically on the parent view  e g  self view   not the child view that has the constraints attached to it   Doing so will update all constrained views  including animating other views that might be constrained to the view that you changed the constraint of  e g  View B is attached to the bottom of View A and you just changed View A s top offset and you want View B to animate with it    Try this   Objective-C  -  void moveBannerOffScreen        self view layoutIfNeeded         UIView animateWithDuration 5         animations                self  addBannerDistanceFromBottomConstraint constant   -32               self view layoutIfNeeded      Called on parent view                 bannerIsVisible   FALSE     -  void moveBannerOnScreen         self view layoutIfNeeded         UIView animateWithDuration 5         animations                self  addBannerDistanceFromBottomConstraint constant   0               self view layoutIfNeeded      Called on parent view                 bannerIsVisible   TRUE      Swift 3  UIView animate withDuration  5        self  addBannerDistanceFromBottomConstraint constant   0     self view layoutIfNeeded

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I appreciate the answer provided  but I think it would be nice to take it a bit further   The basic block animation from the documentation   containerView layoutIfNeeded      Ensures that all pending layout operations have been completed  UIView animateWithDuration 1 0 animations            Make all constraint changes here       containerView layoutIfNeeded      Forces the layout of the subtree animation block and then captures all of the frame changes       but really this is a very simplistic scenario  What if I want to animate subview constraints via the  updateConstraints method   An animation block that calls the subviews updateConstraints method   self view layoutIfNeeded    self subView setNeedsUpdateConstraints    self subView updateConstraintsIfNeeded    UIView animateWithDuration 1 0f delay 0 0f options UIViewAnimationOptionLayoutSubviews animations         self view layoutIfNeeded     completion nil     The updateConstraints method is overridden in the UIView subclass and must call super at the end of the method   -  void updateConstraints          Update some constraints       super updateConstraints       The AutoLayout Guide leaves much to be desired but it is worth reading  I myself am using this as part of a UISwitch that toggles a subview with a pair of UITextFields with a simple and subtle collapse animation  0 2 seconds long   The constraints for the subview are being handled in the UIView subclasses updateConstraints methods as described above

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Working Solution 100  Swift 5 3 i have read all the answers and want to share the code and hierarchy of lines which i have used in all my applications to animate them correctly  Some solutions here are not working  you should check them on slower devices e g iPhone 5 at this moment  self btnHeightConstraint constant   110 UIView animate withDuration  0 27     weak self  in       self  view layoutIfNeeded

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Storyboard  Code  Tips and a few Gotchas  The other answers are just fine but this one highlights a few fairly important gotchas of animating constraints using a recent example  I went through a lot of variations before I realized the following   Make the constraints you want to target into Class variables to hold a strong reference  In Swift I used lazy variables   lazy var centerYInflection NSLayoutConstraint            let temp    self view constraints filter    0 firstItem is MNGStarRating    filter      0 secondItem is UIWebView    filter    0 firstAttribute     CenterY    first         return temp        After some experimentation I noted that one MUST obtain the constraint from the view ABOVE  aka the superview  the two views where the constraint is defined  In the example below  both MNGStarRating and UIWebView are the two types of items I am creating a constraint between  and they are subviews within self view    Filter Chaining  I take advantage of Swift s filter method to separate the desired constraint that will serve as the inflection point  One could also get much more complicated but filter does a nice job here   Animating Constraints Using Swift     Nota Bene - This example is the storyboard code solution and assumes   one has made default constraints in the storyboard  One can then   animate the changes using code    Assuming you create a property to filter with accurate criteria and get to a specific inflection point for your animation  of course you could also filter for an array and loop through if you need multiple constraints    lazy var centerYInflection NSLayoutConstraint         let temp    self view constraints filter    0 firstItem is MNGStarRating    filter      0 secondItem is UIWebView    filter    0 firstAttribute     CenterY    first     return temp              Sometime later      IBAction func toggleRatingView  sender AnyObject        let aPointAboveScene   - max UIScreen mainScreen   bounds width UIScreen mainScreen   bounds height    2 0       self view layoutIfNeeded           Use any animation you want  I like the bounce in springVelocity        UIView animateWithDuration 1 0  delay  0 0  usingSpringWithDamping  0 3  initialSpringVelocity  0 75  options    CurveEaseOut   animations       - gt  Void in            I use the frames to determine if the view is on-screen         if CGRectContainsRect self view frame  self ratingView frame                   in frame   animate away               I play a sound to give the animation some life              self centerYInflection constant   aPointAboveScene             self centerYInflection priority   UILayoutPriority 950             else                  I play a different sound just to keep the user engaged               out of frame   animate into scene             self centerYInflection constant   0             self centerYInflection priority   UILayoutPriority 950              self view setNeedsLayout               self view layoutIfNeeded                  success  - gt  Void in                do something else                      The many wrong turns  These notes are really a set of tips that I wrote for myself  I did all the don ts personally and painfully  Hopefully this guide can spare others    Watch out for zPositioning  Sometimes when nothing is apparently happening  you should hide some of the other views or use the view debugger to locate your animated view  I ve even found cases where a User Defined Runtime Attribute was lost in a storyboard s xml and led to the animated view being covered  while working   Always take a minute to read the documentation  new and old   Quick Help  and headers  Apple keeps making a lot of changes to better manage AutoLayout constraints  see stack views   Or at least the AutoLayout Cookbook  Keep in mind that sometimes the best solutions are in the older documentation videos  Play around with the values in the animation and consider using other animateWithDuration variants  Don t hardcode specific layout values as criteria for determining changes to other constants  instead use values that allow you to determine the location of the view  CGRectContainsRect is one example If needed  don t hesitate to use the layout margins associated with a view participating in the constraint definition  let viewMargins   self webview layoutMarginsGuide  is on example Don t do work you don t have to do  all views with constraints on the storyboard have constraints attached to the property self viewName constraints Change your priorities for any constraints to less than 1000  I set mine to 250  low  or 750  high  on the storyboard   if you try to change a 1000 priority to anything in code then the app will crash because 1000 is required  Consider not immediately trying to use activateConstraints and deactivateConstraints  they have their place but when just learning or if you are using a storyboard using these probably means your doing too much   they do have a place though as seen below  Consider not using addConstraints   removeConstraints unless you are really adding a new constraint in code  I found that most times I layout the views in the storyboard with desired constraints  placing the view offscreen   then in code  I  animate the constraints previously created in the storyboard to move the view around  I spent a lot of wasted time building up constraints with the new NSAnchorLayout class and subclasses  These work just fine but it took me a while to realize that all the constraints that I needed already existed in the storyboard  If you build constraints in code then most certainly use this method to aggregate your constraints    Quick Sample Of Solutions to AVOID when using Storyboards  private var  nc  NSLayoutConstraint           lazy var newConstraints  NSLayoutConstraint               if   self  nc isEmpty                return self  nc                    let viewMargins   self webview layoutMarginsGuide         let minimumScreenWidth   min UIScreen mainScreen   bounds width UIScreen mainScreen   bounds height           let centerY   self ratingView centerYAnchor constraintEqualToAnchor self webview centerYAnchor          centerY constant   -1000 0         centerY priority    950          let centerX    self ratingView centerXAnchor constraintEqualToAnchor self webview centerXAnchor          centerX priority    950           if let buttonConstraints   self originalRatingViewConstraints  filter                  0 firstItem is UIButton     0 secondItem is UIButton                            self  nc appendContentsOf buttonConstraints                      self  nc append  centerY          self  nc append  centerX           self  nc append  self ratingView leadingAnchor constraintEqualToAnchor viewMargins leadingAnchor  constant  10 0           self  nc append  self ratingView trailingAnchor constraintEqualToAnchor viewMargins trailingAnchor  constant  10 0           self  nc append  self ratingView widthAnchor constraintEqualToConstant  minimumScreenWidth - 20 0            self  nc append  self ratingView heightAnchor constraintEqualToConstant 200 0            return self  nc           If you forget one of these tips or the more simple ones such as where to add the layoutIfNeeded  most likely nothing will happen  In which case you may have a half baked solution like this      NB - Take a moment to read the AutoLayout Section Below and the   original guide  There is a way to use these techniques to supplement   your Dynamic Animators    UIView animateWithDuration 1 0  delay  0 0  usingSpringWithDamping  0 3  initialSpringVelocity  1 0  options    CurveEaseOut   animations       - gt  Void in                             if self starTopInflectionPoint constant  lt  0                      -3000                   offscreen                 self starTopInflectionPoint constant   self navigationController  navigationBar bounds height    0                 self changeConstraintPriority  self starTopInflectionPoint   value  UILayoutPriority 950   forView  self ratingView                 else                    self starTopInflectionPoint constant   -3000                  self changeConstraintPriority  self starTopInflectionPoint   value  UILayoutPriority 950   forView  self ratingView                               success  - gt  Void in                do something else                    Snippet from the AutoLayout Guide  note the second snippet is for using OS X   BTW - This is no longer in the current guide as far as I can see   The preferred techniques continue to evolve   Animating Changes Made by Auto Layout  If you need full control over animating changes made by Auto Layout  you must make your constraint changes programmatically  The basic concept is the same for both iOS and OS X  but there are a few minor differences   In an iOS app  your code would look something like the following    containerView layoutIfNeeded      Ensures that all pending layout operations have been completed  UIView animateWithDuration 1 0 animations            Make all constraint changes here       containerView layoutIfNeeded      Forces the layout of the subtree animation block and then captures all of the frame changes       In OS X  use the following code when using layer-backed animations    containterView layoutSubtreeIfNeeded    NSAnimationContext runAnimationGroup   NSAnimationContext  context          context setAllowsImplicitAnimation  YES           Make all constraint changes here       containerView layoutSubtreeIfNeeded         When you aren   t using layer-backed animations  you must animate the constant using the constraint   s animator     constraint animator  setConstant 42     For those who learn better visually check out this early video from Apple   Pay Close Attention  Often in documentation there are small notes or pieces of code that lead to bigger ideas  For example attaching auto layout constraints to dynamic animators is a big idea   Good Luck and May the Force be with you

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Working and just tested solution for Swift 3 with Xcode 8 3 3   self view layoutIfNeeded   self calendarViewHeight constant   56 0  UIView animate withDuration  0 5  delay  0 0  options  UIViewAnimationOptions curveEaseIn  animations            self view layoutIfNeeded          completion  nil    Just keep in mind that self calendarViewHeight is a constraint referred to a customView  CalendarView   I called the  layoutIfNeeded   on self view and NOT on self calendarView  Hope this help

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I was trying to animate Constraints and was not really easy to found a good explanation   What other answers are saying is totally true  you need to call  self view layoutIfNeeded   inside  animateWithDuration  animations   However  the other important point is to have pointers for every NSLayoutConstraint you want to animate   I created an example in GitHub

[ios] How do I animate constraint changes?

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