如果有人想知道如何在iOS 7+中实现这一点，这里有一个解决方案(iOS 6也兼容)

在objective - c中

[self.navigationBar setBackgroundImage:[UIImage new]
                         forBarMetrics:UIBarMetricsDefault];
self.navigationBar.shadowImage = [UIImage new];
self.navigationBar.translucent = YES;

swift 3 (iOS 10)

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

在swift 2中

self.navigationBar.setBackgroundImage(UIImage(), forBarMetrics: .Default)
self.navigationBar.shadowImage = UIImage()
self.navigationBar.translucent = true

讨论

将导航栏上的半透明设置为YES就可以了，这是由于UINavigationBar文档中讨论的行为。我将在这里报告相关片段:

如果在具有不透明自定义背景图像的导航栏上将此属性设置为YES，则导航栏将对图像应用小于1.0的系统不透明度。

你的意思是完全透明，还是使用照片应用程序中看到的半透明黑色?后者你可以通过设置它的barStyle属性为uibarstyleblack半透明来实现。前……我不太确定。如果您希望其中的项仍然可见，您可能必须在栏的视图层次结构中进行一些挖掘，并删除包含其背景的视图。

IOS7:

self.navigationController.navigationBar.translucent = YES;
self.navigationController.navigationBar.shadowImage = [UIImage new];
self.navigationController.view.backgroundColor = [UIColor clearColor];
[self.navigationController.navigationBar setBackgroundImage:[UIImage new] forBarMetrics:UIBarMetricsDefault];
self.navigationController.navigationBar.backgroundColor = [UIColor clearColor];

这适用于Swift 2.0。

navigationController!.navigationBar.setBackgroundImage(UIImage(), forBarMetrics: UIBarMetrics.Default)
navigationController!.navigationBar.shadowImage = UIImage()
navigationController!.navigationBar.translucent = true

下面的代码扩展了为这个线程选择的顶部答案，以消除底部边框并设置文本颜色:

The last two coded lines of this code set transparency. I borrowed that code from this thread and it worked perfectly! The "clipsToBounds" property was code I found which got rid of the bottom border line with OR without transparency set (so if you decide to go with a solid white/black/etc. background instead, there will still be no border line). The "tintColor" line (2nd coded line) set my back button to a light grey I kept barTintColor as a backup. I don't know why transparency would not work, but if it doesn't, I want my bg white as I used to have it let navigationBarAppearace = UINavigationBar.appearance() navigationBarAppearace.tintColor = UIColor.lightGray navigationBarAppearace.barTintColor = UIColor.white navigationBarAppearace.clipsToBounds = true navigationBarAppearace.isTranslucent = true navigationBarAppearace.setBackgroundImage(UIImage(), for: .default) navigationBarAppearace.shadowImage = UIImage()

在按照上面大家说的去做之后，也就是:

navigationController?.navigationBar.setBackgroundImage(UIImage(), forBarMetrics: .default)
navigationController?.navigationBar.shadowImage = UIImage()
navigationController!.navigationBar.isTranslucent = true

．.． 我的导航栏还是白色的。所以我加了这一行:

navigationController?.navigationBar.backgroundColor = .clear

．.． 果不其然!这似乎奏效了。