///隐藏navigationBar导航栏线(直接写在UINavigationController-viewDidLoad方法里面即可)
UIView *backgroundView = [self.navigationBar subviews].firstObject;
_lineView = backgroundView.subviews.firstObject;
_lineView.hidden = YES;
原文：http://www.cnblogs.com/wangkejia/p/7634818.html