从iOS 13开始，就有一个系统API来设置或删除阴影

UIKit使用shadowImage和shadowColor属性来确定阴影的 外观。当shadowImage为nil时，该工具条显示默认的着色阴影 根据shadowColor属性中的值。如果shadowColor为nil或 包含clearColor颜色，条显示没有阴影。

    let appearance = UINavigationBarAppearance()
    appearance.shadowImage = nil
    appearance.shadowColor = nil
    navigationController.navigationBar.standardAppearance = appearance

https://developer.apple.com/documentation/uikit/uibarappearance/3198009-shadowimage

以上问题的答案

//删除1px的导航条线

[[UINavigationBar appearance] setBackgroundImage:[[UIImage alloc]init] forBarMetrics:UIBarMetricsDefault];
[[UINavigationBar appearance] setShadowImage:[[UIImage alloc] init]];
[[UINavigationBar appearance] setTranslucent:NO];
[[UINavigationBar appearance] setTintColor:[UIColor yourColor]];

简单的解决方案

   let navigationBar = self.navigationController?.navigationBar
    navigationBar?.setBackgroundImage(UIImage(), forBarPosition: UIBarPosition.Any, barMetrics: UIBarMetrics.Default)
    navigationBar?.shadowImage = UIImage()

Swift 4测试 单线解决方案

在Viewdidload () 将导航控制器的用户默认值设置为true

override func viewDidLoad() {
    super.viewDidLoad()

    self.navigationController?.navigationBar.setValue(true, forKey: "hidesShadow")

}

pxpgraphics对Swift 3.0的回答。

import Foundation
import UIKit

extension UINavigationBar {

  func hideBottomHairline() {
    let navigationBarImageView = hairlineImageViewInNavigationBar(view: self)
    navigationBarImageView!.isHidden = true
  }

  func showBottomHairline() {
    let navigationBarImageView = hairlineImageViewInNavigationBar(view: self)
    navigationBarImageView!.isHidden = false
  }

  private func hairlineImageViewInNavigationBar(view: UIView) -> UIImageView? {
    if view is UIImageView && view.bounds.height <= 1.0 {
      return (view as! UIImageView)
    }

    let subviews = (view.subviews as [UIView])
    for subview: UIView in subviews {
      if let imageView: UIImageView = hairlineImageViewInNavigationBar(view: subview) {
        return imageView
      }
    }
    return nil
  }
}

extension UIToolbar {

  func hideHairline() {
    let navigationBarImageView = hairlineImageViewInToolbar(view: self)
    navigationBarImageView!.isHidden = true
  }

  func showHairline() {
    let navigationBarImageView = hairlineImageViewInToolbar(view: self)
    navigationBarImageView!.isHidden = false
  }

  private func hairlineImageViewInToolbar(view: UIView) -> UIImageView? {
    if view is UIImageView && view.bounds.height <= 1.0 {
      return (view as! UIImageView)
    }

    let subviews = (view.subviews as [UIView])
    for subview: UIView in subviews {
      if let imageView: UIImageView = hairlineImageViewInToolbar(view: subview) {
        return imageView
      }
    }
    return nil
  }
}

我的方法:

UINavigationBar.appearance().setBackgroundImage(
            UIImage(),
            forBarPosition: .Any,
            barMetrics: .Default)
    var _width:CGFloat! = self.navigationController?.navigationBar.layer.frame.width
            var _height:CGFloat! = self.navigationController?.navigationBar.layer.frame.height
            var navBarBg = UIView(frame:CGRectMake(0, 0, _width, _height))
            //solid color for bg
            navBarBg.backgroundColor = UIColor.orangeColor()
            view.addSubview(navBarBg)