UIPanGestureRecognizer is a concrete subclass of UIGestureRecognizer that looks for panning (dragging) gestures. The user must be pressing one or more fingers on a view while they pan it. Clients implementing the action method for this gesture recognizer can ask it for the current translation and velocity of the gesture.
A panning gesture is continuous. It begins (UIGestureRecognizerStateBegan) when the minimum number of fingers allowed (minimumNumberOfTouches) has moved enough to be considered a pan. It changes (UIGestureRecognizerStateChanged) when a finger moves while at least the minimum number of fingers are pressed down. It ends (UIGestureRecognizerStateEnded) when all fingers are lifted.
Clients of this class can, in their action methods, query the UIPanGestureRecognizer object for the current translation of the gesture (translationInView:) and the velocity of the translation (velocityInView:). They can specify the view whose coordinate system should be used for the translation and velocity values. Clients may also reset the translation to a desired value.
Whole document - UIPanGestureRecognizer
