If I install your library using pod "UINavigationBar+Addition", it doesn't bring in makeTransparent method in cloned code. probably you need to update code version in your podspec file so it can refer to latest changes.

Hey! I based some swift code off of your code, so here it is :)

import Foundation
import UIKit

extension UINavigationBar {

func hideBottomHairline() {
    var imageView: UIImageView? = findHairlineImageViewunder(self)
    if imageView {
        imageView!.hidden = true
    }
}

func showBottomHairline() {
    var imageView: UIImageView? = findHairlineImageViewunder(self)
    if imageView {
        imageView!.hidden = false
    }
}

func findHairlineImageViewunder(view: UIView) -> UIImageView? {
    if (view is UIImageView) && (1.0 >= view.bounds.size.height) {
        return view as? UIImageView
    }
    for subView: AnyObject in view.subviews {
        var imageView: UIImageView? = findHairlineImageViewunder(subView as UIView)
        if imageView {
            return imageView
        }
    }
    return nil
}

}

Apple's discussion on the matter.

Objective-C does not define linker symbols for each function (or method, in Objective-C) - instead, linker symbols are only generated for each class. If you extend a pre-existing class with categories, the linker does not know to associate the object code of the core class implementation and the category implementation. This prevents objects created in the resulting application from responding to a selector that is defined in the category.

I've forked the repo and added a commit which updates the podspec to include -all_load (along with -objC) when setting OTHER_LDFLAGS to see if this would fix the issue, but when I included my forked version of the pod in a project, I receive the same error.

Any thoughts? Have you guys come across this at all?