From Apple’s doc for UIControlEvents:
UIControlEventTouchCancelA system event canceling the current touches for the control.
UIControlEventTouchDownA touch-down event in the control.
UIControlEventTouchDownRepeatA repeated touch-down event in the control; for this event the value of the UITouch tapCount method is greater than one.
UIControlEventTouchDragEnterAn event where a finger is dragged into the bounds of the control.
UIControlEventTouchDragExitAn event where a finger is dragged from within a control to outside its bounds.
UIControlEventTouchDragInsideAn event where a finger is dragged inside the bounds of the control.
UIControlEventTouchDragOutsideAn event where a finger is dragged just outside the bounds of the control.
UIControlEventTouchUpInsideA touch-up event in the control where the finger is inside the bounds of the control.
UIControlEventTouchUpOutsideA touch-up event in the control where the finger is outside the bounds of the control.