UIImageView with aspect fit working with autolayout

APAspectFitImageView.h

//
//  APAspectFitImageView.h
//  autolayout
//
//  Created by Antol Peshkov on 16.10.14.
//  Copyright (c) 2014 Antol Peshkov. All rights reserved.
//

#import <UIKit/UIKit.h>

@interface APAspectFitImageView : UIImageView

@end

APAspectFitImageView.m

//
//  APAspectFitImageView.m
//
//  Created by Antol Peshkov on 16.10.14.
//  Copyright (c) 2014 Antol Peshkov. All rights reserved.
//

#import "APAspectFitImageView.h"

@interface APAspectFitImageView ()
@property (nonatomic, strong) NSLayoutConstraint *aspectRatio;
@end

@implementation APAspectFitImageView

- (void)awakeFromNib
{
    if (self.contentMode == UIViewContentModeScaleAspectFit) {
        [self updateAspectRatioWithImage:self.image];
    }
}

- (void)setImage:(UIImage *)image
{
    [super setImage:image];
    
    if (self.contentMode == UIViewContentModeScaleAspectFit) {
        [self updateAspectRatioWithImage:image];
    }
}

- (void)updateAspectRatioWithImage:(UIImage *)image
{
    if (self.aspectRatio) {
        [self removeConstraint:self.aspectRatio];
    }
    
    CGFloat aspectRatioValue = image.size.height / image.size.width;
    self.aspectRatio = [NSLayoutConstraint constraintWithItem:self
                                                    attribute:NSLayoutAttributeHeight
                                                    relatedBy:NSLayoutRelationEqual
                                                       toItem:self
                                                    attribute:NSLayoutAttributeWidth
                                                   multiplier:aspectRatioValue
                                                     constant:0.f];
    [self addConstraint:self.aspectRatio];
}

@end