Animated Constraints

ViewController.m

@interface ViewController ()

@property (weak, nonatomic) IBOutlet UISwitch *modeSwitch;

@property (weak, nonatomic) IBOutlet UIView *yellowView;

@property (weak, nonatomic) IBOutlet UIView *blueView;

@property (weak, nonatomic) IBOutlet NSLayoutConstraint *viewSpacingContraint;

@property (weak, nonatomic) IBOutlet NSLayoutConstraint *blueViewConstraint;

@end

@implementation ViewController

NSString *modeUserDefaultKey = @”modeUserDefaultKey”;

– (void)viewDidLoad {

    [super viewDidLoad];

    NSUserDefaults *defaults = [NSUserDefaults standardUserDefaults];

    self.modeSwitch.on = [defaults boolForKey:modeUserDefaultKey];

    [self updateConstraintsForMode];

}

– (IBAction)enableMode:(UISwitch *)sender {

    NSUserDefaults *defaults = [NSUserDefaults standardUserDefaults];

    [defaults setBool:sender.isOn forKey:modeUserDefaultKey];

    [defaults synchronize];

    [self.view layoutIfNeeded];

    [UIView animateWithDuration:1.0 animations:^{

        [self updateConstraintsForMode];

        [self.view layoutIfNeeded];

    }];

}

– (void)updateConstraintsForMode {

    if (self.modeSwitch.isOn) {

        self.viewSpacingContraint.constant = 8.0;

        self.blueViewConstraint.priority = UILayoutPriorityDefaultHigh+1;

    } else {

        self.viewSpacingContraint.constant = self.view.frame.size.width;

        self.blueViewConstraint.priority = UILayoutPriorityDefaultHigh–1;

    }

}

@end