3触摸事件About Events in iOS
1、UIKit Makes It Easy for Your App to Detect Gestures
uicontrol、Gesture recognizers（powerful, reusable, and adaptable.）
create your own gesture recognizer to recognize a new gesture
2、An Event Travels Along a Specific Path Looking for an Object to Handle It
事件响应链
UIEvent：封装一系列的触摸事件
对于 motion events，取决于你所使用的framework以及type
the hit-test view:-------the event to the view where the touch occurred.
The lowest view in the view hierarchy that contains the touch point becomes the hit-test view
Motion and remote control events——send to the first responder for handling
hit-test检查order：从super 到sub
so, 超出super的subview的部分，响应不到(super并不包含sub超出super的frame)
A touch object is associated with its hit-test view for its lifetime, even if the touch later moves outside the view.
An object becomes the first responder by doing two things:
1--- Overriding the canBecomeFirstResponder method to return YES.
2-----Receiving a becomeFirstResponder message. If necessary, an object can send itself this message.
If you try to assign the first responder in viewWillAppear:, your object graph is not yet established, so the becomeFirstResponder method returns NO.
Text editing. When a user taps a text field or a text view, that view automatically becomes the first responder. By default, the virtual keyboard appears and the text field or text view becomes the focus of editing. You can display a custom input view instead of the keyboard if it’s appropriate for your app. You can also add a custom input view to any responder object.
