Want UITableView to “snap to cell”

Question

I am displaying fairly large images in a UITableView. As the user scrolls, I\'d like to the table view to always snap the center-most photo in the middle. That

Answer 1

Extending @mikepj answer, (which in turn extended the great answer by @JesseRusak), this code lets you snap to a cell, even when cells have a variable (or unknown) height, and will snap to the next row if you'll scroll over the bottom half of the row, making it more "natural".

Original Swift 4.2 code: (for convenience, this is the actual code I developed and tested)

func scrollViewWillEndDragging(_ scrollView: UIScrollView, withVelocity velocity: CGPoint, targetContentOffset: UnsafeMutablePointer) {
    guard var scrollingToIP = table.indexPathForRow(at: CGPoint(x: 0, y: targetContentOffset.pointee.y)) else {
        return
    }
    var scrollingToRect = table.rectForRow(at: scrollingToIP)
    let roundingRow = Int(((targetContentOffset.pointee.y - scrollingToRect.origin.y) / scrollingToRect.size.height).rounded())
    scrollingToIP.row += roundingRow
    scrollingToRect = table.rectForRow(at: scrollingToIP)
    targetContentOffset.pointee.y = scrollingToRect.origin.y
}

(translated) Objective-C code: (since this question is tagged objective-c)

- (void)scrollViewWillEndDragging:(UIScrollView *)scrollView withVelocity:(CGPoint)velocity targetContentOffset:(inout CGPoint *)targetContentOffset {
    NSIndexPath *scrollingToIP = [self.tableView indexPathForRowAtPoint:CGPointMake(0, targetContentOffset->y)];
    if (scrollingToIP == nil)
        return;
    CGRect scrollingToRect = [table rectForRowAtIndexPath:scrollingToIP];
    NSInteger roundingRow = (NSInteger)(round(targetContentOffset->y - scrollingToRect.origin.y) / scrollingToRect.size.height));
    scrollingToIP.row += roundingRow;
    scrollingToRect = [table rectForRowAtIndexPath:scrollingToIP];
    targetContentOffset->y = scrollingToRect.origin.y;
}