//导航栏背景
[self.navigationController.navigationBar setBackgroundImage:[UIImage imageNamed:@"nav_bargound.png"] forBarMetrics:UIBarMetricsDefault];
//导航栏底部线
self.navigationController.navigationBar.shadowImage =[UIImage imageNamed:@"nav_bargound.png"];
//导航栏背景
[self.navigationController.navigationBar setBackgroundImage:nil forBarMetrics:UIBarMetricsDefault];
//导航栏底部线
self.navigationController.navigationBar.shadowImage =[UIImage imageNamed:@""];
