I've got a a few UIScrollView
on a page. You can scroll them independently or lock them together and scroll them as one. The problem occurs when they are locked.
I use UIScrollViewDelegate
and scrollViewDidScroll:
to track movement. I query the contentOffset
of the UIScrollView
which changed and then reflect change to other scroll views by setting their contentOffset
property to match.
Great.... except I noticed a lot of extra calls. Programmatically changing the contentOffset
of my scroll views triggers the delegate method scrollViewDidScroll:
to be called. I've tried using setContentOffset:animated:
instead, but I'm still getting the trigger on the delegate.
How can I modify my contentOffsets programmatically to not trigger scrollViewDidScroll:
?
Implementation notes....
Each UIScrollView
is part of a custom UIView
which uses delegate pattern to call back to the presenting UIViewController
subclass that handles coordinating the various contentOffset
values.
It is possible to change the content offset of a UIScrollView
without triggering the delegate callback scrollViewDidScroll:
, by setting the bounds of the UIScrollView
with the origin set to the desired content offset.
CGRect scrollBounds = scrollView.bounds;
scrollBounds.origin = desiredContentOffset;
scrollView.bounds = scrollBounds;
Try
id scrollDelegate = scrollView.delegate;
scrollView.delegate = nil;
scrollView.contentOffset = point;
scrollView.delegate = scrollDelegate;
Worked for me.
What about using existing properties of UIScrollView?
func scrollViewDidScroll(_ scrollView: UIScrollView) {
if (scrollView.isTracking || scrollView.isDragging || scrollView.isDecelerating) {
/// The content offset was changed programmatically.
/// Your code goes here.
}
}
Another approach is to add some logic in your scrollViewDidScroll delegate to determine whether or not the change in content offset was triggered programatically or by the user's touch.
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