It adds the controller's view as a subview of the window.
它创建了一个视图控制对象用来管理窗口视图对象的内容。
2
How to find the kind of subview object the view is containing in it?
如何找到对象视图的子视图包含吗?。
3
One way I can do is to set the leading space and trailing space of the top subview with respect to the main view and also centering horizontally in the main view.