在iOS8中，如果你设置UINavigationBar。你可以设置酒吧的背景为无边框的素色。

迅速:

UINavigationBar.appearance().translucent = false
UINavigationBar.appearance().barStyle = UIBarStyle.Black
UINavigationBar.appearance().barTintColor = UIColor.redColor()

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。

如果你只是想使用纯色导航条，并且已经在你的故事板中设置了它，在你的AppDelegate类中使用下面的代码通过外观代理删除1像素的边界:

[[UINavigationBar appearance] setBackgroundImage:[[UIImage alloc] init]
                                  forBarPosition:UIBarPositionAny
                                      barMetrics:UIBarMetricsDefault];

[[UINavigationBar appearance] setShadowImage:[[UIImage alloc] init]];

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
  }
}

在AppDelegate中，这已经全局地改变了导航栏的格式:

 func application(application: UIApplication, didFinishLaunchingWithOptions launchOptions: [NSObject: AnyObject]?) -> Bool {

    UINavigationBar.appearance().setBackgroundImage(UIImage(), forBarPosition: UIBarPosition.Any, barMetrics: UIBarMetrics.Default)
    UINavigationBar.appearance().shadowImage = UIImage()
    UINavigationBar.appearance().tintColor = UIColor.whiteColor()
    UINavigationBar.appearance().barTintColor = UIColor.redColor()
    UINavigationBar.appearance().translucent = false
    UINavigationBar.appearance().clipsToBounds = false
    UINavigationBar.appearance().backgroundColor = UIColor.redColor()
    UINavigationBar.appearance().titleTextAttributes = [NSFontAttributeName : (UIFont(name: "FONT NAME", size: 18))!, NSForegroundColorAttributeName: UIColor.whiteColor()] }

还没有在特定的VC上实现任何不同的东西，但这将帮助90%的人

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()