Weird frame calculation for UITabBar

Question

Sometimes the app shrinks the width of the UITabBar, the 4 icons in the screenshot are usually distributed across the whole width.

Is anyone experiencing this and knows why it happens or even better how to fix/avoid it? I think it started happening with Swift, so maybe another of their awesome optimizations?

Also not sure how to reproduce it, happens around twice a week, maybe rotation, segue or app switch.

This screenshot is from an iPhone6 in portrait mode, but happens on other devices too.

Answer 1

I found the same behavior on iOS9 in two cases:

1) while immediate rotation during the pop-navigation in UINavigationController;

2) on rotation from landscape to portrait while watching full-screen video player and closing player after that.

To solve the problem on iOS8+ you should subclass UITabBarController and implement method from UIContentContainer protocol as follows:

- (void)viewWillTransitionToSize:(CGSize)size withTransitionCoordinator:(id<UIViewControllerTransitionCoordinator>)coordinator
{
    [super viewWillTransitionToSize:size withTransitionCoordinator:coordinator];

    if (!self.tabBar.window) return;

    [coordinator animateAlongsideTransition: ^(id<UIViewControllerTransitionCoordinatorContext>  _Nonnull context) {
         CGRect newBounds = self.tabBar.bounds;
         newBounds.size.width = size.width;
         self.tabBar.bounds = newBounds;

         [self.view.superview setNeedsLayout];
     }
                             completion: nil];
}

If you don't write return string you won't fix the 2nd issue.

Adding same in Swift:

extension UITabBarController {
    public override func viewWillTransitionToSize(size: CGSize, withTransitionCoordinator coordinator: UIViewControllerTransitionCoordinator) {
        super.viewWillTransitionToSize(size, withTransitionCoordinator: coordinator)
        if let _ = self.tabBar.window {
            coordinator.animateAlongsideTransition( { (context) in
                self.tabBar.bounds.size.width = size.width
                self.view.superview?.setNeedsLayout()
                }, completion: nil)
        }
    }
}