IOS 在IOS6中设置navigationBar背景图片 会有一条 黑色阴影 --- 解决方案

//给navigationBar设置背景图片
        if ([self.navigationController.navigationBar respondsToSelector:@selector(setBackgroundImage:forBarMetrics:)]) {
            [self.navigationController.navigationBar setBackgroundImage:[UIImage imageNamed:@"nav_bg.png"] 
forBarMetrics:UIBarMetricsDefault];
        }
        self.navigationController.navigationBar.layer.contents = (id)[UIImage imageNamed:@"nav_bg.png"].CGImage;
        
解决方案 1：
        
[self.navigationController.navigationBar.layer setMasksToBounds:YES];       // 剪切掉多余的背景

解决方案 2：

self.navigationController.navigationBar.clipsToBounds = YES;

解决方案 3：

CustomNavBar *navBar = (CustomNavBar *)self.navigationController.navigationBar;
        [navBar setBackgroundImage:[UIImage imageNamed:@"navigation_bar_gray.png"] forBarMetrics:UIBarMetricsDefault];
        navBar.shadowImage = [[UIImage alloc]init]; // this is what acctually removed the shadow under navigation bar