iOS: How does one animate to new autolayout constr

Question

I've never worked with autolayout constraints before. I have a small new app I'm working on and noticed that the NIB's views are defaulting to autolayout. So, I figured I'd take the opportunity to work with it and try to figure out where Apple is going with this.

First challenge:

I need to resize an MKMapView and I'd like to animate it to the new position. If I do this the way I'm used to:

[UIView animateWithDuration:1.2f
     animations:^{
         CGRect theFrame = worldView.frame;
         CGRect newFrame = CGRectMake(theFrame.origin.x, theFrame.origin.y, theFrame.size.width, theFrame.size.height - 170);
         worldView.frame = newFrame;
}];

...then the MKMapView will 'snap' back to its original height whenever a sibling view gets updated (in my case a UISegmentedControl's title is being updated [myUISegmentedControl setTitle:newTitle forSegmentAtIndex:0]).

So, what I think I want to do is change the constraints of the MKMapView from being equal to the parent view's hight to being relative to the top of the UISegmentedControl that it was covering: V:[MKMapView]-(16)-[UISegmentedControl]

What I want is for the MKMapView height to shorten so that some controls beneath the map view are revealed. To do so I think I need to change the constraint from a fixed full size view to one where the bottom is constrained to the top of a UISegmentedControl...and I'd like it to animate as view shrinks to new size.

How does one go about this?

Edit - this animation is not animating though the bottom of the view does move up 170 instantly:

    [UIView animateWithDuration:1.2f
         animations:^{
             self.nibMapViewConstraint.constant = -170;

    }];

and the nibMapViewConstraint is wired up in IB to the bottom Vertical Space constraint.

Answer 1

There is a very good tutorial from apple itself that explain how to use animation with autolayout. Follow this link and then find the video named "Auto layout by example" It gives some interesting stuff about autolayout and the last part is about how to use animation.

Answer 2

Most people use autolayout to layout items on their views and modify the layout constrains to create animations.

An easy way to do this without a lot of code is creating the UIView you want to animate in Storyboard and then creating a hidden UIView where you want the UIView to end. You can use the preview in xcode to make sure both UIViews are where you want them to be. After that, hide the ending UIView and swap the layout constraints.

There is a podfile for swapping layout constrains called SBP if you don't want to write it yourself.

Here's a tutorial.

Answer 3

After updating your constraint:

[UIView animateWithDuration:0.5 animations:^{[self.view layoutIfNeeded];}];

Replace self.view with a reference to the containing view.

Answer 4

I have made this small demo available. It shows how auto-layout constraints can be changed and animated in a very simple example. Simply take a look at the DemoViewController.m.

Answer 5

This works for me (Both iOS7 and iOS8+). Click on the auto layout constraint you would like to adjust (in interface builder e.g top constraint). Next make this an IBOutlet;

@property (strong, nonatomic) IBOutlet NSLayoutConstraint *topConstraint;

Animate upwards;

    self.topConstraint.constant = -100;    
    [self.viewToAnimate setNeedsUpdateConstraints]; 
    [UIView animateWithDuration:1.5 animations:^{
        [self.viewToAnimate layoutIfNeeded]; 
    }];

Animate back to original place

    self.topConstraint.constant = 0;    
    [self.viewToAnimate setNeedsUpdateConstraints];  
    [UIView animateWithDuration:1.5 animations:^{
        [self.viewToAnimate layoutIfNeeded];
    }];

Answer 6

No need to use more IBOutlet reference of the constraint instead of this you can directly access or update already applied constraint either applied by Programmatically or from Interface Builder on any view using the KVConstraintExtensionsMaster library. This library is also managing the Cumulative behavior of NSLayoutConstraint.

To add Height Constraint on containerView

 CGFloat height = 200;
 [self.containerView applyHeightConstrain:height];

To update Height Constraint of containerView with animation

[self.containerView accessAppliedConstraintByAttribute:NSLayoutAttributeHeight completion:^(NSLayoutConstraint *expectedConstraint){
        if (expectedConstraint) {
            expectedConstraint.constant = 100;

            /* for the animation */ 
            [self.containerView  updateModifyConstraintsWithAnimation:NULL];
      }
    }];