iOS 7 zooming is not working in ScrollView with AutoLayout but working in iOS8/9

Question

I have made a demo for zoom image using UIScrollView. My ViewController only contains one image. The problem is the image cannot zoom in iO7 (I have tested on iPhone4S-iOS7) but work perfectly in iOS8/iOS9.
Any ideas on how to fix it?

Here is my code

#import "ViewController.h"

@interface ViewController ()<UIScrollViewDelegate>
@property (weak, nonatomic) IBOutlet UIScrollView *scrollview;
@property (weak, nonatomic) IBOutlet UIView *contentview;

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
        float minimumScale = [_contentview frame].size.width /[_scrollview frame].size.width;
        _scrollview.maximumZoomScale = 5;  //Change as per you need
        _scrollview.minimumZoomScale = minimumScale;  //Change as you need
        _scrollview.zoomScale = minimumScale;
        _scrollview.delegate =self;
        _scrollview.clipsToBounds = YES;
}

- (UIView *)viewForZoomingInScrollView:(UIScrollView *)scrollView{
    return self.contentview;
}

@end

Here is the layout structure

Screen.png constraint ContentView constraint

ScrollView constraint

Here is my demo project

https://drive.google.com/file/d/0B679aXO0SBmMeUVHTUdOcmxJSXM/view

Answer 1

The height and width constraints are causing this in iOS 7. A workaround would be, removing those constraints for iOS 7 and calculate minimumScale manually. in IOS 8 and above, do not change anything.

- (void)viewDidLoad {
    [super viewDidLoad];

    float minimumScale = 1;

    if (floor(NSFoundationVersionNumber) < NSFoundationVersionNumber_iOS_8_0) {
        [self.view removeConstraints:self.heightWidthConstraints];
        minimumScale = self.scrollview.frame.size.width / self.imageView.image.size.width;
    }

    _scrollview.maximumZoomScale = 5;  //Change as per you need
    _scrollview.minimumZoomScale = minimumScale;  //Change as you need
    //_scrollview.zoomScale = minimumScale;
    _scrollview.delegate = self;
    //_scrollview.clipsToBounds = YES;

    [self.scrollview setZoomScale:minimumScale animated:YES];
}