设置导航栏的背景颜色和字体

[self.navigationController.navigationBar setBackgroundImage:[UIImage imageNamed:@"OffLineNavView"] forBarMetrics:UIBarMetricsDefault];

[self.navigationController.navigationBar setTitleTextAttributes:[NSDictionary dictionaryWithObjectsAndKeys:[UIColor whiteColor],UITextAttributeTextColor,nil]];

[self.navigationController.navigationBar setTitleTextAttributes:

@{NSFontAttributeName:[UIFont systemFontOfSize:24],

NSForegroundColorAttributeName:[UIColor whiteColor]}];