自定义UINavigationController背景

转载自：http://blog.youkuaiyun.com/lovenjoe/article/details/7646301

 Activity *activity = [[Activity alloc]initWithStyle:UITableViewStylePlain];

    UINavigationController *activityNav = [[UINavigationController alloc]initWithRootViewController:activity];

    activityNav.navigationBar.barStyle = UIBarStyleBlack;

    [activityNav.navigationBar setBackgroundImage:[UIImage imageNamed:@"0.png"] forBarMetrics:UIBarMetricsDefault ];