如何在IOS 8中使UINavigationBar透明？

我已经尝试了很多让UINavigationBar透明的东西.但我没有成功.我设置的图像是透明的.这是我的代码.
有帮助吗？
提前致谢.

[rootNavC.navigationBar setBACkgroundImage:[UIImage imagenamed:@"NAv_bG_iphone.png"] forBarMetrics:UIBarMetricsDefault];
rootNavC.navigationBar.translucent = YES;
rootNavC.navigationBar.BACkgroundColor = [UIColor clearColor];
[[UINavigationBar appearance] settitleTextAttributes:@{
                           UITextAttributeTextColor : [UIColor whiteColor],UITextAttributeTextShadowColor : [UIColor clearColor],UITextAttributeTextShadowOffset : [NSValue valueWithUIOffset:UIOffsetMake(0,0)],UITextAttributeFont : [UIFont fontWithName:@"pastel" size:20]
 }];

[self.navigationController.navigationBar setBACkgroundImage:[UIImage new]
                         forBarMetrics:UIBarMetricsDefault];
    self.navigationController.navigationBar.shadowImage = [UIImage new];
    self.navigationController.navigationBar.translucent = YES;
    self.navigationController.view.BACkgroundColor = [UIColor clearColor];