Events and touches

The events managed by iOS during user interaction are grouped into three main sets:

• Multitouch events are generated by the interaction with the screen

• Motion events are sensed by the accelerometer

• Remote-control events are mostly originated by external accessories

Even if these events are extremely different, they can be encapsulated and handled by the same class: UIEvent. An event instance can be easily distinguished by checking its type property, a UIEventType enum, with the following declaration:

enum UIEventType : Int {
    case Touches
    case Motion
    case RemoteControl
}

When users interact with the screen, a multitouch sequence is generated. Each step of a sequence is described by the same UIEvent instance that carries a set of UITouch objects: one per each of the user's fingers taking part in the multitouch sequence.

The event instance remains the same for the whole sequence, and the same is true for the touch instances that are updated during the sequence, preventing...