导航栏透明

1.

self.navigationController.navigationBar.barTintColor = BACKGROUND_COLOR;//颜色

[[[self.navigationController.navigationBar subviews]objectAtIndex:0] setAlpha:0.1];//透明度

//去掉导航栏的边界黑线

self.navigationController.navigationBar.shadowImage =
[[UIImage alloc] init];

2.

lt_setBackgroundColor http://tech.glowing.com/cn/change-uinavigationbar-backgroundcolor-dynamically/
3.

先做一张全通道全透明的图片1*1的像素就行，取名navigation_bar_background.png作为UINavigationBar的背景色，然后讲barStyle设置成通道就可以了。

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

self.navigationController.navigationBar.barStyle = UIBarStyleBlackTranslucent;

//去掉导航栏的边界黑线

self.navigationController.navigationBar.shadowImage =
[[UIImage alloc] init];