SelfSizingScroller

Fixes scrollToRow/ItemAtIndexPath: for Self Sizing Cells

Self sizing cells in UITableView and UICollectionView are great, but they make scrollToRowAtIndexPath: and scrollToItemAtIndexPath: stop working reliably.

This small library adds a reallyScrollTo... variants to UITableView and UICollectionView that reliably scroll to the right position by doing the scrolling itself using CADisplayLink, and adjusting when needed.

for UITableView:

public func reallyScrollToRow(at indexPath: IndexPath,
                              at scrollPosition: UITableView.ScrollPosition,
                              insets: UIEdgeInsets = .zero,
                              animated: Bool,
                              completion: ((UITableView, _ hasCompleted: Bool) -> Void)? = nil)

for UICollectionView:

func reallyScrollToItem(at indexPath: IndexPath,
                        at scrollPosition: UICollectionView.ScrollPosition, 
                        insets: UIEdgeInsets = .zero,
                        animated: Bool,
                        completion: ((UICollectionView, _ hasCompleted: Bool) -> Void)? = nil)

Extras

Additional Insets

You can specify additional insets that will be respected when scrolling. For example, if you want to scroll a row 10 points below the top, you can use at: .top, insets: UIEdgeInsets(top: 10, left: 0, bottom: 0, right: 0)

CompletionHandler

There’s an optional completionHandler that will be called when scrolling is done with a hasCompleted flag to indicate if we fully scrolled to the designated offset or if we were interrupted.

isScrolling flag

Additionally, checking scrollView.scroller.isScrolling also works to see if we’re currently in a scroll animation.

Extendable

The actual scrolling and determining where to scroll to are separated, so it’s easy to extend by implementing a single method in a protocol:

protocol ScrollOffsetProviderProtocol {
  func targetScrollOffset(witStartOffset startOffset: CGPoint) -> CGPoint?
}

and then call:

class MyScrollOffsetProvider: ScrollOffsetProviderProtocol {
 func targetScrollOffset(witStartOffset startOffset: CGPoint) -> CGPoint? {
   // calculate actual position, gets called on every animation frame.
   // It's fine to return different positions on each invocation,
   // as long as it eventually stabilizes (otherwise we'll scroll
   // forever).
   return ...;
 }
}

let scrollView = UIScrollView()
let provider = MyScrollOffsetProvider()
scrollView.startScrolling(with: provider, animated: true)

Just dynamically return which offset to scroll to and the library will make it happen.