Moving away a view smoothly above a UIWebView using insets and auto layout

ViewController.m

//
//  ViewController.m
//  webviewscroll
//
//  Created by Mats Melke on 2014-01-28.
//  Copyright (c) 2014 Mats Melke. All rights reserved.
//

#import "ViewController.h"

#define SYSTEM_VERSION_GREATER_THAN_OR_EQUAL_TO(v)  ([[[UIDevice currentDevice] systemVersion] compare:v options:NSNumericSearch] != NSOrderedAscending)


@interface ViewController ()
@property(strong, nonatomic) IBOutlet UIWebView *webView;
@property(strong, nonatomic) IBOutlet UIView *adView;
@property(nonatomic, strong) id <UIScrollViewDelegate> originalScrollViewDelegate;
@property(nonatomic, strong) UIScrollView *webViewScrollView;
@property(strong, nonatomic) IBOutlet NSLayoutConstraint *adViewTopMarginConstraint;
@property(strong, nonatomic) IBOutlet NSLayoutConstraint *webViewTopMarginConstraint;
@end

@implementation ViewController {
    CGFloat statusBarHeight;
    CGFloat topViewHeight;
}

- (void)viewDidLoad {
    [super viewDidLoad];

    topViewHeight = self.adView.frame.size.height;

    self.adView.translatesAutoresizingMaskIntoConstraints = NO;
    self.webView.translatesAutoresizingMaskIntoConstraints = NO;

    // Shift views in >=IOS7 to prevent the top view to appear beneath the status bar
    if (SYSTEM_VERSION_GREATER_THAN_OR_EQUAL_TO(@"7.0")) {
        statusBarHeight = 20.0;
    } else {
        statusBarHeight = 0.0;
    }

    self.adViewTopMarginConstraint.constant = statusBarHeight;
    self.webViewTopMarginConstraint.constant = 0.0;

    // Get hold of the scrollview in the webview, and replace the scrollview delegate
    for (UIView *subView in self.webView.subviews) {
        if ([subView isKindOfClass:[UIScrollView class]]) {
            _webViewScrollView = (UIScrollView *) subView;
            _originalScrollViewDelegate = _webViewScrollView.delegate;
            _webViewScrollView.delegate = self;
        }
    }

    self.webViewScrollView.contentInset = UIEdgeInsetsMake(topViewHeight, 0.0, 0.0, 0.0);

    // Load an url
    NSURLRequest *requestObj = [NSURLRequest requestWithURL:[NSURL URLWithString:@"http://www.macrumors.com"]];
    [self.webView loadRequest:requestObj];
}


#pragma mark UIGestureRecognizerDelegate impl

- (BOOL)gestureRecognizer:(UIGestureRecognizer *)gestureRecognizer shouldRecognizeSimultaneouslyWithGestureRecognizer:(UIGestureRecognizer *)otherGestureRecognizer {
    return YES;
}

#pragma mark UIScrollViewDelegate impl
// We must propagate all scrollview delegate calls, because we don't really know what Apple's UIWebView
// implementation does with the callback, now and in the future


- (void)scrollViewDidScroll:(UIScrollView *)scrollView {

    if (scrollView == self.webView.scrollView) {
        [self.originalScrollViewDelegate scrollViewDidScroll:scrollView];
        NSLog(@"webview contentoffset = %f, contentSize = %@", scrollView.contentOffset.y, NSStringFromCGSize(scrollView.contentSize));
        if (scrollView.contentOffset.y >= statusBarHeight) {
            // When the webview content has reached the top, we should always place the adView offscreen
            self.adViewTopMarginConstraint.constant = -1.0 * topViewHeight;
        } else if (scrollView.contentOffset.y <= -1.0 * topViewHeight) {
            // The adView should never be moved further down than just below the status bar
            self.adViewTopMarginConstraint.constant = statusBarHeight;
        } else {
            // Move the adView along with the webview scrolling
            self.adViewTopMarginConstraint.constant = -1.0 * (topViewHeight + scrollView.contentOffset.y) + statusBarHeight;
            NSLog(@"adview margin = %f", self.adViewTopMarginConstraint.constant);
        }
    }
}

- (void)scrollViewDidZoom:(UIScrollView *)scrollView {
    if (scrollView == self.webView.scrollView) {
        [self.originalScrollViewDelegate scrollViewDidZoom:scrollView];
    }
}

- (void)scrollViewWillBeginDragging:(UIScrollView *)scrollView {
    if (scrollView == self.webView.scrollView) {
        [self.originalScrollViewDelegate scrollViewWillBeginDragging:scrollView];
    }
}

- (void)scrollViewWillEndDragging:(UIScrollView *)scrollView withVelocity:(CGPoint)velocity targetContentOffset:(inout CGPoint *)targetContentOffset {
    if (scrollView == self.webView.scrollView) {
        [self.originalScrollViewDelegate scrollViewWillEndDragging:scrollView withVelocity:velocity targetContentOffset:targetContentOffset];
    }
}

- (void)scrollViewDidEndDragging:(UIScrollView *)scrollView willDecelerate:(BOOL)decelerate {
    if (scrollView == self.webView.scrollView) {
        [self.originalScrollViewDelegate scrollViewDidEndDragging:scrollView willDecelerate:decelerate];
    }
}

- (void)scrollViewWillBeginDecelerating:(UIScrollView *)scrollView {
    if (scrollView == self.webView.scrollView) {
        [self.originalScrollViewDelegate scrollViewWillBeginDecelerating:scrollView];
    }
}

- (void)scrollViewDidEndDecelerating:(UIScrollView *)scrollView {
    if (scrollView == self.webView.scrollView) {
        [self.originalScrollViewDelegate scrollViewDidEndDecelerating:scrollView];
    }
}

- (void)scrollViewDidEndScrollingAnimation:(UIScrollView *)scrollView {
    if (scrollView == self.webView.scrollView) {
        [self.originalScrollViewDelegate scrollViewDidEndScrollingAnimation:scrollView];
    }
}

- (UIView *)viewForZoomingInScrollView:(UIScrollView *)scrollView {
    if (scrollView == self.webView.scrollView) {
        return [self.originalScrollViewDelegate viewForZoomingInScrollView:scrollView];
    } else {
        // If this controller is used as delegate for any other scrollview than the webview, you should return your zoomable view here
        return nil;
    }
}

- (void)scrollViewWillBeginZooming:(UIScrollView *)scrollView withView:(UIView *)view {
    if (scrollView == self.webView.scrollView) {
        [self.originalScrollViewDelegate scrollViewWillBeginZooming:scrollView withView:view];
    }
}

- (void)scrollViewDidEndZooming:(UIScrollView *)scrollView withView:(UIView *)view atScale:(float)scale {
    if (scrollView == self.webView.scrollView) {
        [self.originalScrollViewDelegate scrollViewDidEndZooming:scrollView withView:view atScale:scale];
    }
}

- (BOOL)scrollViewShouldScrollToTop:(UIScrollView *)scrollView {
    // We need to return YES for the webview (status bar tapping)
    if (scrollView == self.webView.scrollView) {
        return YES;
    } else {
        return NO;
    }

}

- (void)scrollViewDidScrollToTop:(UIScrollView *)scrollView {
    if (scrollView == self.webView.scrollView) {
        [self.originalScrollViewDelegate scrollViewDidScrollToTop:scrollView];
    }
}


@end