More fiddling with how Jump to Present works
Now, when loading present items, they're inserted into the data source immediately along with a gap. If the user taps Jump to Present, then a new snapshot _with only the present items_ will be applied (which allows infinite scrolling to work properly when they scroll back down) and the view scrolled-to-top. Tapping Go Back, then, applies the original snapshot (i.e., the current one from when Jump to Present was tapped) and restores the scroll position.
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@ -412,7 +412,7 @@ class TimelineViewController: UIViewController, TimelineLikeCollectionViewContro
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// I'm not sure whether this should move into TimelineLikeController/TimelineLikeCollectionViewController
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let (_, presentItems) = await (loadNewerAndEndRefreshing(), try? loadInitial())
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if let presentItems, !presentItems.isEmpty {
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insertPresentItemsIfNecessary(presentItems)
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insertPresentItemsAndShowJumpToast(presentItems)
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}
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}
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}
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@ -430,13 +430,13 @@ class TimelineViewController: UIViewController, TimelineLikeCollectionViewContro
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UIAccessibility.post(notification: .screenChanged, argument: self.collectionView.cellForItem(at: IndexPath(row: 0, section: 0)))
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}
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} else {
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insertPresentItemsIfNecessary(presentItems)
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insertPresentItemsAndShowJumpToast(presentItems)
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}
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}
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}
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private func insertPresentItemsIfNecessary(_ presentItems: [String]) {
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let snapshot = dataSource.snapshot()
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private func insertPresentItemsAndShowJumpToast(_ presentItems: [String]) {
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var snapshot = dataSource.snapshot()
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guard snapshot.indexOfSection(.statuses) != nil else {
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return
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}
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@ -444,13 +444,38 @@ class TimelineViewController: UIViewController, TimelineLikeCollectionViewContro
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if case .status(id: let firstID, _, _) = currentItems.first,
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// if there's no overlap between presentItems and the existing items in the data source, prompt the user
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!presentItems.contains(firstID) {
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let applySnapshotBeforeScrolling: Bool
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// create a new snapshot to reset the timeline to the "present" state
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var snapshot = NSDiffableDataSourceSnapshot<Section, Item>()
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snapshot.appendSections([.statuses])
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snapshot.appendItems(presentItems.map { .status(id: $0, collapseState: .unknown, filterState: .unknown) }, toSection: .statuses)
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// remove any existing gap, if there is one
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if let index = currentItems.lastIndex(of: .gap) {
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snapshot.deleteItems(Array(currentItems[index...]))
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let statusesSection = snapshot.indexOfSection(.statuses)!
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if collectionView.indexPathsForVisibleItems.contains(IndexPath(row: index, section: statusesSection)) {
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// the gap cell is on screen
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applySnapshotBeforeScrolling = false
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} else if let topMostVisibleCell = collectionView.indexPathsForVisibleItems.first(where: { $0.section == statusesSection }),
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index < topMostVisibleCell.row {
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// the gap cell is above the top, so applying the snapshot would remove the currently-viewed statuses
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applySnapshotBeforeScrolling = false
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} else {
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// the gap cell is below the bottom of the screen
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applySnapshotBeforeScrolling = true
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}
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} else {
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// there is no existing gap
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applySnapshotBeforeScrolling = true
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}
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snapshot.insertItems([.gap], beforeItem: currentItems.first!)
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snapshot.insertItems(presentItems.map { .status(id: $0, collapseState: .unknown, filterState: .unknown) }, beforeItem: .gap)
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var config = ToastConfiguration(title: "Jump to present")
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if applySnapshotBeforeScrolling {
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let firstVisibleIndexPath = collectionView.indexPathsForVisibleItems.min()!
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let firstVisibleItem = dataSource.itemIdentifier(for: firstVisibleIndexPath)!
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applySnapshot(snapshot, maintainingBottomRelativeScrollPositionOf: firstVisibleItem)
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}
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var config = ToastConfiguration(title: "Jump to Present")
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config.edge = .top
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config.systemImageName = "arrow.up"
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config.dismissAutomaticallyAfter = 4
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@ -467,19 +492,24 @@ class TimelineViewController: UIViewController, TimelineLikeCollectionViewContro
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} else {
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origItemAtTop = nil
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}
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self.dataSource.apply(snapshot, animatingDifferences: true) {
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// when the user explicitly taps Jump to Present, we drop all the old items to let infinite scrolling work properly when they scroll back down
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var snapshot = NSDiffableDataSourceSnapshot<Section, Item>()
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snapshot.appendSections([.statuses])
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snapshot.appendItems(presentItems.map { .status(id: $0, collapseState: .unknown, filterState: .unknown) }, toSection: .statuses)
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// don't animate the snapshot change, the scrolling animation will paper over the switch
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self.dataSource.apply(snapshot, animatingDifferences: false) {
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self.collectionView.scrollToItem(at: IndexPath(row: 0, section: 0), at: .top, animated: true)
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var config = ToastConfiguration(title: "Go back")
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var config = ToastConfiguration(title: "Go Back")
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config.edge = .top
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config.systemImageName = "arrow.down"
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config.dismissAutomaticallyAfter = 4
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config.dismissAutomaticallyAfter = 2
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config.action = { [unowned self] toast in
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toast.dismissToast(animated: true)
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// todo: it would be nice if we could animate this, but that doesn't work with the screen-position-maintaining stuff
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if let (item, offset) = origItemAtTop {
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self.applySnapshot(snapshot, maintainingScreenPosition: offset, ofItem: item)
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self.applySnapshot(origSnapshot, maintainingScreenPosition: offset, ofItem: item)
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} else {
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self.dataSource.apply(origSnapshot, animatingDifferences: false)
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}
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@ -516,12 +546,17 @@ class TimelineViewController: UIViewController, TimelineLikeCollectionViewContro
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// firstItemAfterOriginalGapOffsetFromTop without intruding into unmeasured area
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var cur = indexPathOfItemToMaintain
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var amountScrolledUp: CGFloat = 0
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var first = true
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while true {
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if cur.row <= 0 {
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break
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}
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if let cell = self.collectionView.cellForItem(at: indexPathOfItemToMaintain),
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cell.convert(.zero, to: self.view).y - self.view.safeAreaInsets.top > offsetFromTop {
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// if we're breaking from the loop at the first iteration, we need to make sure to still call scrollToItem for the current row
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if first {
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self.collectionView.scrollToItem(at: cur, at: .top, animated: false)
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}
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break
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}
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cur = IndexPath(row: cur.row - 1, section: cur.section)
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@ -529,6 +564,7 @@ class TimelineViewController: UIViewController, TimelineLikeCollectionViewContro
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self.collectionView.layoutIfNeeded()
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let attrs = self.collectionView.layoutAttributesForItem(at: cur)!
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amountScrolledUp += attrs.size.height
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first = false
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}
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self.collectionView.contentOffset.y += amountScrolledUp
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self.collectionView.contentOffset.y -= offsetFromTop
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