objective c - Negative spacer for UIBarButtonItem in navigation bar on iOS 11

Question

In iOS 10 and below, there was a way to add a negative spacer to the buttons array in the navigation bar, like so:

UIBarButtonItem *negativeSpacer = [[UIBarButtonItem alloc] initWithBarButtonSystemItem:UIBarButtonSystemItemFixedSpace target:nil action:nil];
negativeSpacer.width = -8;
self.navigationItem.leftBarButtonItems = @[negativeSpacer, [self backButtonItem]];

This no longer works on iOS 11 (the spacer becomes positive, instead of negative). I have inspected the view hierarchy of the bar button item, and it is now embedded into _UIButtonBarStackView. How to adjust the position of the bar button on iOS 11?

Answer 1

EDIT:

This may no longer work as of iOS 13. You may get the error:

Client error attempting to change layout margins of a private view

OLD ANSWER:

I found a somewhat hacky solution on the Apple developer forums: https://forums.developer.apple.com/thread/80075

It looks like the problem comes from how iOS 11 handles the UIBarButtonItem .fixedSpace buttons and how a UINavigationBar is laid out in iOS 11. The navigation bars now use autolayout and the layout margins to layout the buttons. The solution presented in that post (at the bottom) was to set all the layout margins to some value you want.

class InsetButtonsNavigationBar: UINavigationBar {

    override func layoutSubviews() {
        super.layoutSubviews()

        for view in subviews {
            // Setting the layout margins to 0 lines the bar buttons items up at
            // the edges of the screen. You can set this to any number to change
            // the spacing.
            view.layoutMargins = .zero
        }
    }

}

To use this new nav bar with custom button spacing, you will need to update where you create any navigation controllers with the following code:

let navController = UINavigationController(navigationBarClass: InsetButtonsNavigationBar.self, 
                                                 toolbarClass: UIToolbar.self)
navController.viewControllers = [yourRootViewController]