去掉导航栏的黑线

for (UIView *subview1 in self.navigationController.navigationBar.subviews) {
        
        for (UIView *subView2 in subview1.subviews) {
            
            if ([subView2 isKindOfClass:[UIImageView class]] && subView2.frame.size.height==0.5) {
                
                [subView2 removeFromSuperview];
                
            }
            
        }
        
    }