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Improve scroll position maintenance

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Justin Mazzocchi 2020-11-02 15:05:09 -08:00
parent df15a8e8af
commit 69b664ce0f
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GPG key ID: E223E6937AAFB01C
1 changed files with 11 additions and 18 deletions
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29
ViewModels/Sources/ViewModels/CollectionItemsViewModel.swift
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@ -267,7 +267,7 @@ private extension CollectionItemsViewModel {
}
func process(items: [[CollectionItem]]) {
maintainScrollPositionItemId = itemForScrollPositionMaintenance(newItems: items)?.itemId
maintainScrollPositionItemId = idForScrollPositionMaintenance(newItems: items)
self.items.send(items)
let itemsSet = Set(items.reduce([], +))
@ -275,25 +275,18 @@ private extension CollectionItemsViewModel {
viewModelCache = viewModelCache.filter { itemsSet.contains($0.key) }
}
// swiftlint:disable:next cyclomatic_complexity function_body_length
func itemForScrollPositionMaintenance(newItems: [[CollectionItem]]) -> CollectionItem? {
func idForScrollPositionMaintenance(newItems: [[CollectionItem]]) -> CollectionItem.Id? {
let flatItems = items.value.reduce([], +)
let flatNewItems = newItems.reduce([], +)
if let markerTimeline = collectionService.markerTimeline,
identification.appPreferences.positionBehavior(markerTimeline: markerTimeline) == .rememberPosition,
let localLastReadId = identification.service.getLocalLastReadId(markerTimeline),
!hasRememberedPosition,
let lastReadItem = flatNewItems.first(where: {
switch $0 {
case let .status(status, _):
return status.id == localLastReadId
default:
return false
}
}) {
flatItems.contains(where: { $0.itemId == localLastReadId }),
!hasRememberedPosition {
hasRememberedPosition = true
return lastReadItem
return localLastReadId
}
if collectionService is ContextService,
@ -303,9 +296,8 @@ private extension CollectionItemsViewModel {
return configuration.isContextParent // Maintain scroll position of parent after initial load of context
}) {
return contextParent
return contextParent.itemId
} else if collectionService is TimelineService {
let flatItems = items.value.reduce([], +)
let difference = flatNewItems.difference(from: flatItems)
if let lastSelectedLoadMore = lastSelectedLoadMore {
@ -320,7 +312,7 @@ private extension CollectionItemsViewModel {
return status.id == loadMore.beforeStatusId
}) {
return statusAfterLoadMore
return statusAfterLoadMore.itemId
}
}
}
@ -330,9 +322,10 @@ private extension CollectionItemsViewModel {
let topVisibleItem = items.value[topVisibleIndexPath.section][topVisibleIndexPath.item]
if newItems.count > topVisibleIndexPath.section,
let newIndex = newItems[topVisibleIndexPath.section].firstIndex(of: topVisibleItem),
let newIndex = newItems[topVisibleIndexPath.section]
.firstIndex(where: { $0.itemId == topVisibleItem.itemId }),
newIndex > topVisibleIndexPath.item {
return topVisibleItem
return topVisibleItem.itemId
}
}
}