iOS 完全透明navigationBar以及隐藏透明后的黑色线

页面要实现透明NavigationBar使用下面的方法

[self.navigationController.navigationBar setBackgroundImage:[UIImage new] forBarMetrics:UIBarMetricsCompact];

让tableView之类的起始点在最上方设置

self.automaticallyAdjustsScrollViewInsets = NO;

接下来是navigationBar透明后黑线的问题

@interface MyViewController () {
    UIImageView *navBarHairlineImageView;
}
@end
@implementation MyViewController
- (void)viewDidLoad {
    [super viewDidLoad];
    [self.navigationController.navigationBar setBackgroundImage:[UIImage new] forBarMetrics:UIBarMetricsCompact];
    navBarHairlineImageView = [self findHairlineImageViewUnder:self.navigationController.navigationBar];
    self.automaticallyAdjustsScrollViewInsets = NO;
}
- (UIImageView *)findHairlineImageViewUnder:(UIView *)view {
    if ([view isKindOfClass:UIImageView.class] && view.bounds.size.height <= 1.0) {
        return (UIImageView *)view;
    }
    for (UIView *subview in view.subviews) {
        UIImageView *imageView = [self findHairlineImageViewUnder:subview];
        if (imageView) {
            return imageView;
        }
    }
    return nil;
}
- (void)viewWillAppear:(BOOL)animated {
    [super viewWillAppear:animated];
    navBarHairlineImageView.hidden = YES;
}
- (void)viewWillDisappear:(BOOL)animated {
    [super viewWillDisappear:animated];
    navBarHairlineImageView.hidden = NO;   
}

也可以用更简单的

if ([self.navigationController.navigationBar respondsToSelector:@selector( setBackgroundImage:forBarMetrics:)]){
        NSArray *list = self.navigationController.navigationBar.subviews;
        for (id obj in list) {
            if ([obj isKindOfClass:[UIImageView class]]) {
                UIImageView *imageView = (UIImageView *)obj;
                NSArray *list2 = imageView.subviews;
                for (id obj2 in list2) {
                    if ([obj2 isKindOfClass:[UIImageView class]]) {
                        UIImageView *imageView2 = (UIImageView *)obj2;
                        imageView2.hidden = YES;
                    }
                }
            }
        }
    }