whatswrong?

#import "ViewController.h"

@interface ViewController ()
@property (nonatomic) IBOutlet UIScrollView *myScrollView;

@end

@implementation ViewController
@synthesize myScrollView;

- (void)mySetup {
    myScrollView = [[UIScrollView alloc] initWithFrame:CGRectMake(0, 0, self.view.frame.size.width, (self.view.frame.size.height/2))];
    myScrollView.backgroundColor = [UIColor redColor];
    NSLayoutConstraint *widthConstraint = [NSLayoutConstraint constraintWithItem:self.view
                                                                       attribute:NSLayoutAttributeWidth
                                                                       relatedBy:NSLayoutRelationEqual
                                                                          toItem:myScrollView
                                                                       attribute:NSLayoutAttributeWidth
                                                                      multiplier:1.0
                                                                        constant:0];

    NSLayoutConstraint *heightConstraint = [NSLayoutConstraint constraintWithItem:self.view
                                                                       attribute:NSLayoutAttributeHeight
                                                                       relatedBy:NSLayoutRelationEqual
                                                                          toItem:myScrollView
                                                                       attribute:NSLayoutAttributeHeight
                                                                      multiplier:1.0
                                                                        constant:0];

    myScrollView.translatesAutoresizingMaskIntoConstraints = NO;
    NSLog( @"WHATDOWEHAVE %@", widthConstraint );
    [self.view addSubview:myScrollView];
    [self.view addConstraints:@[widthConstraint, heightConstraint]];


}


- (void)viewDidLoad {
    [super viewDidLoad];
    [self mySetup];
//    [self.view addSubview:myScrollView];

}

- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}

@end