First, the event processing mechanism
Events are when the user's finger touches the screen, or slides on the screen, or shakes the device, etc., the system continuously sends these events to the application object through messages. There are three kinds of events that can be captured in iOS devices: touch events, movement events and multimedia remote control events.
A touch event is an event generated by operations such as touch and movement on the user's screen, and it collects information through the touch screen of the device.
Second, touch events
Temporal: The temporal information, called the phase, indicates whether the touch has just started, is moving or is stationary, and when it ends, that is, when the finger is lifted from the screen.
Spatial aspects: The touch object also includes the position information in the current view or window, as well as the previous position information.
Reference: "iOS Sensor Application Development Best Practices"