对于任何想在Swift 2.x中这样做的人:

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

或Swift 3.x:

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

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

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
}}

试试下面这段代码:

self.navigationController.navigationBar.translucent = YES;

extension UINavigationBar {
var isTransperent: Bool {
        get {
            return false // Just to satisfy property
        }
        set {
            if newValue {
                self.shadowImage = UIImage()
                self.isTranslucent = true
                self.setBackgroundImage(UIImage(), for: .default)
            } else {
                self.shadowImage = UIImage()
                self.isTranslucent = false
                self.setBackgroundImage(nil, for: .default)
            }
        }
    }
}