topLayoutGuide in child view controller

Question

I have a UIPageViewController with translucent status bar and navigation bar. Its topLayoutGuide is 64 pixels, as expected.

However, the ch

Answer 1

While this answer might be correct, I still found myself having to travel the containment tree up to find the right parent view controller and get what you describe as the "real topLayoutGuide". This way I can manually implement automaticallyAdjustsScrollViewInsets.

This is how I'm doing it:

In my table view controller (a subclass of UIViewController actually), I have this:

- (void)viewWillLayoutSubviews {
    [super viewWillLayoutSubviews];

    _tableView.frame = self.view.bounds;

    const UIEdgeInsets insets = (self.automaticallyAdjustsScrollViewInsets) ? UIEdgeInsetsMake(self.ms_navigationBarTopLayoutGuide.length,
                                                                                               0.0,
                                                                                               self.ms_navigationBarBottomLayoutGuide.length,
                                                                                               0.0) : UIEdgeInsetsZero;
    _tableView.contentInset = _tableView.scrollIndicatorInsets = insets;
}

Notice the category methods in UIViewController, this is how I implemented them:

@implementation UIViewController (MSLayoutSupport)

- (id<UILayoutSupport>)ms_navigationBarTopLayoutGuide {
    if (self.parentViewController &&
        ![self.parentViewController isKindOfClass:UINavigationController.class]) {
        return self.parentViewController.ms_navigationBarTopLayoutGuide;
    } else {
        return self.topLayoutGuide;
    }
}

- (id<UILayoutSupport>)ms_navigationBarBottomLayoutGuide {
    if (self.parentViewController &&
        ![self.parentViewController isKindOfClass:UINavigationController.class]) {
        return self.parentViewController.ms_navigationBarBottomLayoutGuide;
    } else {
        return self.bottomLayoutGuide;
    }
}

@end

Hope this helps :)

Answer 2

This is an unfortunate behavior that appears to have been rectified in iOS 11 with the safe-area API revamp. That said, you will always get the correct value off the root view controller. For example, if you want the upper safe area height pre-iOS 11:

Swift 4

let root = UIApplication.shared.keyWindow!.rootViewController!
let topLayoutGuideLength = root.topLayoutGuide.length

Answer 3

The documentation says to use topLayoutGuide in viewDidLayoutSubviews if you are using a UIViewController subclass, or layoutSubviews if you are using a UIView subclass.

If you use it in those methods you should get an appropriate non-zero value.

Documentation link: https://developer.apple.com/library/ios/documentation/UIKit/Reference/UIViewController_Class/Reference/Reference.html#//apple_ref/occ/instp/UIViewController/topLayoutGuide

Answer 4

This has been addressed in iOS 8.

How to set topLayoutGuide position for child view controller

Essentially, the container view controller should constrain the child view controller's (top|bottom|left|right)LayoutGuide as it would any other view. (In iOS 7, it was already fully constrained at a required priority, so this didn't work.)

Answer 5

Swifty implementation of @NachoSoto answer:

extension UIViewController {

    func navigationBarTopLayoutGuide() -> UILayoutSupport {
        if let parentViewController = self.parentViewController {
            if !parentViewController.isKindOfClass(UINavigationController) {
                return parentViewController.navigationBarTopLayoutGuide()
            }
        }

        return self.topLayoutGuide
    }

    func navigationBarBottomLayoutGuide() -> UILayoutSupport {
        if let parentViewController = self.parentViewController {
            if !parentViewController.isKindOfClass(UINavigationController) {
                return parentViewController.navigationBarBottomLayoutGuide()
            }
        }

        return self.bottomLayoutGuide
    }
}