试试下面这段代码:

self.navigationController.navigationBar.translucent = YES;

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];

c# / Xamarin解决方案

NavigationController.NavigationBar.SetBackgroundImage(new UIImage(), UIBarMetrics.Default);
NavigationController.NavigationBar.ShadowImage = new UIImage();
NavigationController.NavigationBar.Translucent = true;

这适用于Swift 2.0。

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

另一种方式，为我工作是子类UINavigationBar和留下drawRect方法空!!

@IBDesignable class MONavigationBar: UINavigationBar {


// Only override drawRect: if you perform custom drawing.
// An empty implementation adversely affects performance during animation.
override func drawRect(rect: CGRect) {
    // Drawing code
}}

对于Swift 3.0:

override func viewDidLoad() {
    super.viewDidLoad()

    navigationController?.navigationBar.setBackgroundImage(UIImage(), for: .default)
    navigationController?.navigationBar.shadowImage = UIImage()
    navigationController?.navigationBar.isTranslucent = true
}