How to Hide Uinavigationbar 1Px Bottom Line

How to hide UINavigationBar 1px bottom line

For iOS 13:

Use the .shadowColor property

If this property is nil or contains the clear color, the bar displays no shadow

For instance:

let navigationBar = navigationController?.navigationBar
let navigationBarAppearance = UINavigationBarAppearance()
navigationBarAppearance.shadowColor = .clear
navigationBar?.scrollEdgeAppearance = navigationBarAppearance

For iOS 12 and below:

To do this, you should set a custom shadow image. But for the shadow image to be shown you also need to set a custom background image, quote from Apple's documentation:

For a custom shadow image to be shown, a custom background image must
also be set with the setBackgroundImage(_:for:) method. If the default
background image is used, then the default shadow image will be used
regardless of the value of this property.

So:

let navigationBar = navigationController!.navigationBar
navigationBar.setBackgroundImage(#imageLiteral(resourceName: "BarBackground"),
                                                        for: .default)
navigationBar.shadowImage = UIImage()

Above is the only "official" way to hide it. Unfortunately, it removes bar's translucency.

I don't want background image, just color##

You have those options:

Solid color, no translucency:

 navigationBar.barTintColor = UIColor.redColor()
 navigationBar.isTranslucent = false
 navigationBar.setBackgroundImage(UIImage(), for: .default)
 navigationBar.shadowImage = UIImage()

Create small background image filled with color and use it.
Use 'hacky' method described below. It will also keep bar translucent.

How to keep bar translucent?##

To keep translucency you need another approach, it looks like a hack but works well. The shadow we're trying to remove is a hairline UIImageView somewhere under UINavigationBar. We can find it and hide/show it when needed.

Instructions below assume you need hairline hidden only in one controller of your UINavigationController hierarchy.

Declare instance variable:

private var shadowImageView: UIImageView?

Add method which finds this shadow (hairline) UIImageView:

private func findShadowImage(under view: UIView) -> UIImageView? {
    if view is UIImageView && view.bounds.size.height <= 1 {
        return (view as! UIImageView)
    }

    for subview in view.subviews {
        if let imageView = findShadowImage(under: subview) {
            return imageView
        }
    }
    return nil
}

Add/edit viewWillAppear/viewWillDisappear methods:

override func viewWillAppear(_ animated: Bool) {
    super.viewWillAppear(animated)

    if shadowImageView == nil {
        shadowImageView = findShadowImage(under: navigationController!.navigationBar)
    }
    shadowImageView?.isHidden = true
}

override func viewWillDisappear(_ animated: Bool) {
    super.viewWillDisappear(animated)

    shadowImageView?.isHidden = false
}

The same method should also work for UISearchBar hairline,
and (almost) anything else you need to hide :)

Many thanks to @Leo Natan for the original idea!