1     /*
 2      
 3      NSObject -> CALayer ->CAShapeLayer(CAGradientLayer)
 4      
 5      NSObject -> UIImage
 6      
 7      NSObject -> UIResponder -> UIView -> UIScrollView -> UITableView(UICollectionView)
 8      
 9      NSObject -> UIResponder -> UIView -> UIControl -> UIButton
10      
11      */