设置全局导航栏颜色，标题大小和UIBarButtonItem字体大小

swift：

UINavigationBar.appearance().barTintColor = UIColor.init(red: 47, green: 48, blue: 52)

UINavigationBar.appearance().tintColor = UIColor.whiteColor()

UINavigationBar.appearance().titleTextAttributes = [NSFontAttributeName: UIFont.boldSystemFontOfSize(18),NSForegroundColorAttributeName: UIColor.whiteColor()]

UIBarButtonItem.appearance().setTitleTextAttributes([NSFontAttributeName: UIFont.boldSystemFontOfSize(15),NSForegroundColorAttributeName: UIColor.whiteColor()], forState: UIControlState.Normal)

oc：

#pragma mark -  设置全局返回按钮，无文字

[[UIBarButtonItem appearance] setBackButtonTitlePositionAdjustment:UIOffsetMake(0, -60) forBarMetrics:UIBarMetricsDefault];

如果需要设置导航栏颜色，使barItem颜色也被渲染了，可以这样设置（就可以保证barItem里面图片的颜色不被渲染了）
self.navigationItem.rightBarButtonItem = [[UIBarButtonItem alloc] initWithImage: [[UIImage imageNamed: @"xiaoxi_icon"] imageWithRenderingMode: UIImageRenderingModeAlwaysOriginal] style: UIBarButtonItemStylePlain target: self action: @selector(a)];

如果导航栏与view出现了空隙。需要把系统默认设置空隙值关掉

#pragma 设置控制器，出现默认知道空隙
self.automaticallyAdjustsScrollViewInsets = NO;