→The View Hierarchy
[[Image:ipad_view_heirachy_user_interface.jpg|An iPad user interface illustrating the view hierarchy]]
In this example, the UIWindow instance is not visible because it is fully obscured by the blue UIView1 instance. Displayed on top of, and within the frame of, UIView1 are the UIButton1, UILabel and yellow UIView2 subviews. Displayed on top of, and within the frame of, UIView2 are its respective subviews, namely UIButton2 and UIImageView.