UITapGestureRecognizer is a concrete subclass of UIGestureRecognizer that looks for single or multiple taps.
For the gesture to be recognized, the specified number of fingers must tap the view a specified number of times.
Although taps are discrete gestures, they are discrete for each state of the gesture recognizer; thus the associated action message is sent when the gesture begins and is sent for each intermediate state until (and including) the ending state of the gesture. Code that handles tap gestures should therefore test for the state of the gesture.
Whole document - UITapGestureRecognizer