What's the velocity unit in scrollViewWillEndDragging:withVelocity:targetContentOffset:?

Question

The documentation states it's points (per second, I'm assuming)? However, the values I get for it are in the (.5, 3.5) range. The scroll view then travels several hundred points before coming to a halt. The actual initial velocity should be different by orders of magnitude.

Manifold

I thought those could be screen or view heights (widths) but that wasn't it either. – Manifold

Perhaps it's in points per screen-refresh-interval, which is 1/60th of a second. Touch events are reported at the screen refresh interval, so this would make sense. – Fourdrinier

I guess it could be, thanks. Problem is, there's still no way to get any meaningful data (e.g. time until it stops) out of the method - because we don't know the deceleration curve. – Manifold

Definitely file a bug requesting a documentation improvement here. Have you tried per-millisecond? – Horsewhip

What are you attempting to do? Perhaps there is another way of looking at it? – Perpetrate

Answer 1

It is points/millisecond. From UIScrollView.h:

// called on finger up if the user dragged. velocity is in points/millisecond. targetContentOffset may be changed to adjust where the scroll view comes to rest
- (void)scrollViewWillEndDragging:(UIScrollView *)scrollView withVelocity:(CGPoint)velocity targetContentOffset:(inout CGPoint *)targetContentOffset NS_AVAILABLE_IOS(5_0);

This is from iOS 7 SDK, which seemed more plausible given the very low values they've been returning in velocity.

Testudo

Answer 2

From Docs

called on finger up if the user dragged. velocity is in points/millisecond. targetContentOffset may be changed to adjust where the scroll view comes to rest

Owain