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]];

在Xamarin Forms中，这对我来说很管用。只需在AppDelegate.cs上添加这个:

UINavigationBar.Appearance.ShadowImage = new UIImage();

快速做这件事的方法:

UINavigationBar.appearance().setBackgroundImage(UIImage(), for: .any, barMetrics: .default)
UINavigationBar.appearance().shadowImage = UIImage()

pxpgraphics的解决方案为Swift 2.0更新

extension UINavigationBar {

    func hideBottomHairline()
    {
        hairlineImageViewInNavigationBar(self)?.hidden = true
    }

    func showBottomHairline()
    {
        hairlineImageViewInNavigationBar(self)?.hidden = false
    }

    private func hairlineImageViewInNavigationBar(view: UIView) -> UIImageView?
    {
        if let imageView = view as? UIImageView where imageView.bounds.height <= 1
        {
            return imageView
        }

        for subview: UIView in view.subviews
        {
            if let imageView = hairlineImageViewInNavigationBar(subview)
            {
                return imageView
            }
        }

        return nil
    }

}

extension UIToolbar
{

    func hideHairline()
    {
        let navigationBarImageView = hairlineImageViewInToolbar(self)?.hidden = true
    }

    func showHairline()
    {
        let navigationBarImageView = hairlineImageViewInToolbar(self)?.hidden = false
    }

    private func hairlineImageViewInToolbar(view: UIView) -> UIImageView?
    {
        if let imageView = view as? UIImageView where imageView.bounds.height <= 1
        {
            return imageView
        }

        for subview: UIView in view.subviews
        {
            if let imageView = hairlineImageViewInToolbar(subview)
            {
                return imageView
            }
        }

        return nil
    }

}

这里有一个非常简单的解决方案:

self.navigationController.navigationBar.clipsToBounds = YES;

酒吧风格的黑色适合我。

[[UINavigationBar appearance] setBarStyle:UIBarStyleBlack];

我拥有的所有属性(以防万一):

    [[UINavigationBar appearance] setBarTintColor:color];
    [[UINavigationBar appearance] setTranslucent:NO];
    [[UINavigationBar appearance] setShadowImage:[UIImage new]];
    [[UINavigationBar appearance] setBarStyle:UIBarStyleBlack];