How can I get how the Scrollview is moving? - ios

Question

I'm trying to move a view while the scrollview is being scrolled with the same intensity.
I'm trying:
- (void)scrollViewDidScroll:(UIScrollView *)scrollView {
// here I detect when user scroll
}
How could I get the intensity that the scrollview is being scrolled?

Answer 1

Try to use these methods:
- (void)scrollViewWillBeginDragging:(UIScrollView *)scrollView
{
//scrolling on
NSLog(#"scrollViewWillBeginDragging");
}
- (void)scrollViewDidEndDragging:(UIScrollView *)scrollView willDecelerate:(BOOL)decelerate
{
if(!decelerate) {
//not scrolling
}
NSLog(#"scrollViewDidEndDragging");
}

Answer 2

You can do that by reading the contentOffset property on the scrollView
// You can save this as a property or an iVar
CGPoint lastContentOffset;
-(void)scrollViewWillBeginDragging:(UIScrollView *)scrollView{
lastContentOffset = scrollView.contentOffset;
}
-(void)scrollViewDidScroll:(UIScrollView *)scrollView {
CGPoint difference = CGPointSubstract(scrollView.contentOffset, lastContentOffset);
lastContentOffset = scrollView.contentOffset;
// Use difference to know by how much the scroll view scrolled
// IMPORTANT: CGPointSubstract is not a standard function, you can implement it yourself.
}

Answer 3

I don't want to give you the full code but i'll help with how to achieve it.
1) You need to use the time.
2) When the time difference is greater than an amount of time passed to measure (0.05s?)
3) Check what the old content offset is compared to the new one
4) The difference is your velocity
5) reset your current timer
6) set current offsets to last offset
Hope this helps
Ben
distance calcs
CGFloat distanceY = currentOffset.y - lastOffset.y;
CGFloat distanceX = currentOffset.X - lastOffset.X;