UICollectionView-分隔scrollViewDidScroll和scrollToItemAtIndexPath

Question

My screen has a calendar view and below it a UICollectionView with a list of events ordered by date.

When the user changes the month in the calendar, I scroll the collection view to that month's events using UICollectionView scrollToItemAtIndexPath .

When the user scrolls through the UICollectionView , I use scrollViewDidScroll and UICollectionView indexPathsForVisibleItems to detect the scrolling and change the calendar to match the month for the events that are visible.

Now, the problem is that changing the calendar month calls scrollToItemAtIndexPath , which triggers scrollViewDidScroll , which changes the calendar month, which... you get the idea.

Is there any way to separate the two calls? I guess what I want is to only call scrollViewDidScroll if it's triggered by the user scrolling, but I'm happy with any other solution that reaches my goal.

Answer 1

UICollectionView inherits from UIScrollView . You can therefore access the tracking property to determine "whether the user has touched the content to initiate scrolling."

The seemingly obtuse wording there refers to the fact that the user may have started touching but not yet started scrolling. However if the view is scrolling without the user having started touching it then it's safe to assume a programmatic scroll.

Answer 2

This is what I ended up doing - feels hacky, but it works. If anyone has cleaner ways to do it, I'm happy to hear it.

- (void)scrollViewDidScroll:(UIScrollView *)scrollView {
    // Don't change calendar month if currently scrolling
    if (scrolling)
        return;

    // change calendar month
}

- (void)scrollEventsToCurrentMonth {
    // find index path
    // scroll to index path

     scrolling = TRUE;
     [self performSelector:@selector(stoppedScrolling) withObject:NULL afterDelay:0.5];
}

- (void)stoppedScrolling {
    scrolling = FALSE;
}