Sometimes you want to require users to use two fingers instead of one when scrolling content with
UIScrollViews. GarageBand, for example, does this with its on-screen piano keyboards, this way scrolling between octaves does not trigger key presses.
While you could implement this by overriding event handling code, there’s an easier approach. As of iOS 5,
UIScrollView exposes the gesture recognizer responsible for scrolling content via the
panGestureRecognizer property. To require two-finger scrolling, you can simply change its
minimumNumberOfTouches property to