UIButton -> UIControl -> UIView -> UIResponder -> NSObject
The base class for controls, which are visual elements that convey a specific action or intention in response to user interactions.
An object that manages the content for a rectangular area on the screen.
An abstract interface for responding to and handling events. (ex: Touch Events、Motion Events、Press Events)
The root class of most Objective-C class hierarchies, from which subclasses inherit a basic interface to the runtime system and the ability to behave as Objective-C objects.