gesture recognition - What is the difference between Pan and Swipe in iOS?

Question

Sounds simple .. Hold the Trackpad, move the finger, release .. But somehow swipe is not being triggered (pan is triggered instead)

UISwipeGestureRecognizer *swipeGesture = [[UISwipeGestureRecognizer alloc] 
      initWithTarget:v action:@selector(handleSwipe:)];
swipeGesture.direction= UISwipeGestureRecognizerDirectionUp;
[v addGestureRecognizer:swipeGesture];

Pan is recognized by the above sequence instead.

UIPanGestureRecognizer *panGesture = [[UIPanGestureRecognizer alloc] 
      initWithTarget:v action:@selector(handlePan:)];
[v addGestureRecognizer: panGesture];

If pan is commented, swipe is recognized by the same gesture .. With this, 2 questions:

• What is the difference then between a pan and a swipe?
• How can one simulate a swipe on iPhone simulator?

Answer 1

By definition, a swipe gesture is necessarily also a pan gesture -- both involve translational movement of touch points. The difference is in the recognizer semantics: a pan recognizer looks for the beginning of translational movement and continues to report movement in any direction over time, while a swipe recognizer makes an instantaneous decision as to whether the user's touches moved linearly in the required direction.

By default, no two recognizers will recognize the same gesture, so there's a conflict between pan and swipe. Most likely, your pan recognizer "wins" the conflict because its gesture is simpler / more general: A swipe is a pan but a pan may not be a swipe, so the pan recognizes first and excludes other recognizers.

You should be able to resolve this conflict using the delegate method gestureRecognizer:shouldRecognizeSimultaneouslyWithGestureRecognizer:, or perhaps without delegation by making the pan recognizer depend on the swipe recognizer with requireGestureRecognizerToFail:.

With the conflict resolved, you should be able to simulate a one-finger swipe by quickly dragging the mouse. (Though as the mouse is more precise than your finger, it's a bit more finicky than doing the real thing on a device.) Two-finger pan/swipe can be done by holding the Option & Shift keys.