if #available(iOS 13.0, *) {
            let appearance = UINavigationBarAppearance()
            appearance.backgroundColor          = Colors.color_app
            appearance.titleTextAttributes      = [.foregroundColor : UIColor.white]
            appearance.largeTitleTextAttributes = [.foregroundColor : UIColor.white]
            appearance.shadowColor = .clear
            appearance.shadowImage = UIImage()
            
            UINavigationBar.appearance().tintColor            = .white
            UINavigationBar.appearance().standardAppearance   = appearance
            UINavigationBar.appearance().compactAppearance    = appearance
            UINavigationBar.appearance().scrollEdgeAppearance = appearance
        } else {
            UINavigationBar.appearance().barTintColor        = Colors.color_app
            UINavigationBar.appearance().tintColor           = .white
            UINavigationBar.appearance().titleTextAttributes = [NSAttributedString.Key.foregroundColor : UIColor.white]
            if #available(iOS 11.0, *) {
                UINavigationBar.appearance().largeTitleTextAttributes = [NSAttributedString.Key.foregroundColor: UIColor.white]
            }
            UINavigationBar.appearance().isTranslucent = false
            
            UINavigationBar.appearance().shadowImage = UIImage()
            UINavigationBar.appearance().setBackgroundImage(UIImage(), for: .default)
        }

在Swift 3中，我们就是这样做的

对于任何视图控制器:

navigationBar.shadowImage = UIImage()
setBackgroundImage(UIImage(), for: .default)

对于整个应用程序:

UINavigationBar.appearance().setBackgroundImage(UIImage(),barMetrics: .Default)
UINavigationBar.appearance().shadowImage = UIImage()

设置背景图像的问题是它消除了模糊。您可以在不设置背景图像的情况下删除它。在这里看到我的答案。

[tabviewController.view setBackgroundColor:[UIColor blackColor]];

对我来说[UIColor blackColor]可能是你的背景色， tabviewController是你的UITabBarController，如果你正在使用它!

想把Serhii回答的Swift版本加进去。我用下面的代码创建了一个uibareextension .swift:

import Foundation
import UIKit

extension UINavigationBar {
    func hideBottomHairline() {
        self.hairlineImageView?.isHidden = true
    }

    func showBottomHairline() {
        self.hairlineImageView?.isHidden = false
    }
}

extension UIToolbar {
    func hideBottomHairline() {
        self.hairlineImageView?.isHidden = true
    }

    func showBottomHairline() {
        self.hairlineImageView?.isHidden = false
    }
}

extension UIView {
    fileprivate var hairlineImageView: UIImageView? {
        return hairlineImageView(in: self)
    }

    fileprivate func hairlineImageView(in view: UIView) -> UIImageView? {
        if let imageView = view as? UIImageView, imageView.bounds.height <= 1.0 {
            return imageView
        }

        for subview in view.subviews {
            if let imageView = self.hairlineImageView(in: subview) { return imageView }
        }

        return nil
    }
}

我也遇到了同样的问题，但没有一个答案真正令人满意。以下是我对Swift3的看法:

func hideNavigationBarLine() {
    navigationController?.navigationBar.setBackgroundImage(UIImage(), for: .default)
    navigationController?.navigationBar.shadowImage = UIImage()
}

只需在viewDidLoad()中调用它。