Interrupting a scrolling/animating UIScrollView with a UIGestureRecognizer - iphone

Question

I have a UIScrollView and a UITapGestureRecognizerwhich are both pretty basic, and have got them to work together in every way I need except one. The UIScrollView doesn't use any zooming, and the UITapGestureRecognizer just writes to the console for now.
I can get the UITapGestureRecognizer to write to the console when the UIScrollView is tapped, either while stationary or animating through setContentOffset, but I cannot get it to work when the UIScrollView is moving due to being swiped. When the UIScrollView is swiped and still in motion, the first tap after swiping will stop it moving, and then only the second tap is picked up by the UITapGestureRecognizer. I hope to get the first tap to both stop the UIScrollView from scrolling and also write to the console through the UITapGestureRecognizer.
I hope that my problem here is just through a gap in my knowledge of either the UIScrollView or UITapGestureRecognizer and there is just a Property to set to fix this, but so far no amount of reading has helped me with this issue. Any ideas on whether this is possible?
Edit: Thanks for the suggestions, please see below
Apologies, I don't think I explained myself very well. I realise the first movement on the stationary UIScrollView is a swipe (which in my case is just handled by the UIScrollView btw, not a gesture recognizer).
The problem is after swiping and releasing, if you tap while it is still in motion (and no other touch is in progress), it isn't picked up by the UITapGestureRecognizer, instead it is only picked up by the UIScrollView and stops the UIScrollView moving. If you let it decelerate then tap, this works fine. Also if it is moving due to an animation but not a swipe, the tap also works fine.
This is the same when using a `UILongPressGestureRecognizer' which is what I want to use ideally, but thought if I can't get it to work with a tap, I have no chance with that!

Answer 1

Sounds like you need to implement the
- (BOOL)gestureRecognizer:(UIGestureRecognizer *)gestureRecognizer shouldRecognizeSimultaneouslyWithGestureRecognizer:(UIGestureRecognizer *)otherGestureRecognizer
delegate method for your UITapGestureRecognizer and return YES for the UIGestureRecognizers you want to interpret tap gestures in sync with.
e.x.
// Somewhere in your code...
UIGestureRecognizer *tap = [[UITapGestureRecognizer alloc] init];
tap.delegate = self;
[self.view addGestureRecognizer:tap];
[tap release];
// And the delegate method...
- (BOOL)gestureRecognizer:(UIGestureRecognizer *)gestureRecognizer shouldRecognizeSimultaneouslyWithGestureRecognizer:(UIGestureRecognizer *)otherGestureRecognizer {
return YES;
}
n.b. You may want to be more discriminating in deciding which UIGestureRecognizer(s) you wish to work in sync with. The example will work with every other gesture recognizer.

Answer 2

The problem is that when the user taps the first time to scroll the UIScrollView, this is not a tap, it is a swipe. It would be considered a tap only when the user taps and releases the finger almost at the same position (without dragging the finger through the screen).
What you could do to solve your problem is: use the UIScrollView delegate method scrollViewWillBeginDragging and then you would know when the user just tapped and will start dragging the scrollview, and also add the UITapGestureRecognizer for those real taps.