Animating an UIImageView (View) from Point A to Point B with constraints programmatically

Question

I have an image view that I have lined up on the center right of my screen. All is fine when adding the image view by itself with constraints. I need to animate the image view from that original position(Point A) to the bottom portion(Point B) of the screen; the problem is when I try to animate from Point A to Point B, the image view starts off in the upper left hand corner of the screen, like it was simply added with no constraints (as opposed to where I want it starting off in the center) .

Here is the code and some comments:

#define DEGREES_TO_RADIANS(x) (M_PI * x / 180.0) //defined above
- (void)viewDidLoad
{
UIImage *cardFaceDownImage = [UIImage imageNamed:@"b-top@2x.png"];
UIImageView *dealCardDown = [[UIImageView alloc] initWithImage:cardFaceDownImage];
dealCardDown.translatesAutoresizingMaskIntoConstraints = NO;

NSLayoutConstraint *dealCardConstraintY = [NSLayoutConstraint constraintWithItem:dealCardDown attribute:NSLayoutAttributeCenterY relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeCenterY multiplier:1 constant:1];

NSLayoutConstraint *dealCardConstraintX = [NSLayoutConstraint constraintWithItem:dealCardDown attribute:NSLayoutAttributeCenterX relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeCenterX multiplier:1 constant:130];

[self.view addConstraint:dealCardConstraintY];
[self.view addConstraint:dealCardConstraintX];
[self.view addSubview:dealCardDown];

//IF I comment out the below code the UIImageView lines up where I want it (Point A)
//IF I don't coment it out, the imageview starts in the upper left hand corner of the screen
//where it normally would as if just adding an image view programatically without
//constraints would, but it does end up where I want it to (Point B)

[self.view removeConstraint:dealCardConstraintX];
[self.view removeConstraint:dealCardConstraintY];

dealCardConstraintY = [NSLayoutConstraint constraintWithItem:dealCardDown attribute:NSLayoutAttributeCenterY relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeBottom multiplier:1 constant:1];

dealCardConstraintX = [NSLayoutConstraint constraintWithItem:dealCardDown attribute:NSLayoutAttributeCenterX relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeLeft multiplier:1 constant:130];

[self.view addConstraint:dealCardConstraintY];
[self.view addConstraint:dealCardConstraintX];

[self.view setNeedsUpdateConstraints];

[UIView animateWithDuration:2.0 delay:2.0 options:UIViewAnimationCurveEaseIn animations:^(void)
 {
     dealCardDown.transform = CGAffineTransformRotate(dealCardDown.transform, DEGREES_TO_RADIANS(90));

     [self.view layoutIfNeeded];

 }
 completion:^(BOOL finished)
 { 
 }
 ];
 }

..

Answer 1

You need to move change of constraint into animation block, so it will be animated properly. This code works for me well.

- (void)viewDidAppear:(BOOL)animated
{
[super viewDidAppear:animated];

UIView *dealCardDown = [[UIView alloc] initWithFrame:(CGRect){0,0,50,50}];
dealCardDown.backgroundColor = [UIColor redColor];
dealCardDown.translatesAutoresizingMaskIntoConstraints = NO;
NSLayoutConstraint *sizeConstraint = [NSLayoutConstraint constraintWithItem: dealCardDown attribute: NSLayoutAttributeWidth relatedBy: NSLayoutRelationEqual toItem: nil attribute:NSLayoutAttributeNotAnAttribute multiplier: 1 constant: 50];
[dealCardDown addConstraint:sizeConstraint];
sizeConstraint = [NSLayoutConstraint constraintWithItem: dealCardDown attribute: NSLayoutAttributeHeight relatedBy: NSLayoutRelationEqual toItem: nil attribute:NSLayoutAttributeNotAnAttribute multiplier: 1 constant: 50];
[dealCardDown addConstraint:sizeConstraint];
[self.view addSubview:dealCardDown];

NSLayoutConstraint *dealCardConstraintX = [NSLayoutConstraint constraintWithItem:dealCardDown attribute:NSLayoutAttributeCenterX relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeCenterX multiplier:1.f constant:0.f];
NSLayoutConstraint *dealCardConstraintY = [NSLayoutConstraint constraintWithItem:dealCardDown attribute:NSLayoutAttributeBottom relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeBottom multiplier:1.f constant:-self.view.center.y+dealCardDown.frame.size.height/2];


[self.view addConstraint:dealCardConstraintX];
[self.view addConstraint:dealCardConstraintY];
[self.view layoutIfNeeded];

[UIView animateWithDuration:2.0 delay:0.0 options:UIViewAnimationCurveEaseIn animations:^(void)
 {
     dealCardDown.transform = CGAffineTransformRotate(dealCardDown.transform, 90*M_PI/180);
     dealCardConstraintY.constant = 0;
     [self.view layoutIfNeeded];

 }
                 completion:^(BOOL finished)
 { 
 }
 ];
}