Adds a view to the end of the receiver’s list of subviews.
SWIFT func addSubview(_ view: UIView) OBJECTIVE-C - (void)addSubview:(UIView * _Nonnull)view
The view to be added. After being added, this view appears on top of any other subviews.
This method establishes a strong reference to view and sets its next responder to the receiver, which is its new superview.
Views can have only one superview. If view already has a superview and that view is not the receiver, this method removes the previous superview before making the receiver its new superview.