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Remember offset of collection views during table view reload to avoid…
… jitter
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Riot/Modules/Common/Recents/RecentsContentOffsetStore.swift
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| // | ||
| // Copyright 2022 New Vector Ltd | ||
| // | ||
| // Licensed under the Apache License, Version 2.0 (the "License"); | ||
| // you may not use this file except in compliance with the License. | ||
| // You may obtain a copy of the License at | ||
| // | ||
| // http://www.apache.org/licenses/LICENSE-2.0 | ||
| // | ||
| // Unless required by applicable law or agreed to in writing, software | ||
| // distributed under the License is distributed on an "AS IS" BASIS, | ||
| // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. | ||
| // See the License for the specific language governing permissions and | ||
| // limitations under the License. | ||
| // | ||
|
|
||
| import Foundation | ||
| import UIKit | ||
|
|
||
| /** | ||
| Types of sections as defined in `RecentsDataSource`, albeit represented as an enum for stronger type safety | ||
| */ | ||
| enum RecentsDataSourceSectionType { | ||
| case crossSigningBanner | ||
| case secureBackupBanner | ||
| case directory | ||
| case invites | ||
| case favorites | ||
| case people | ||
| case conversation | ||
| case lowPriority | ||
| case serverNotice | ||
| case suggestedRooms | ||
| } | ||
|
|
||
| /** | ||
| A store of content offsets for a special type of table view where each cell contains a collection view, | ||
| and the content offset needs to be preserved across table view reloads. | ||
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| This type of table view is used on some of the tabs (e.g. home), where vertical rows represent sections | ||
| (favourites, people, rooms ... ) and horizontal represents different rooms (shown in a collection view). | ||
| When such a table view is reloaded, it will dequeue and reuse the previously created collection views | ||
| in random order, meaning that any contentOffset they may have had will now be arbitrarily swapped around. | ||
| The store allows saving the current content offsets per section and restoring them after a reload. | ||
| */ | ||
| @objc class RecentsContentOffsetStore: NSObject { | ||
| private var contentOffsets = [RecentsDataSourceSectionType: CGPoint]() | ||
|
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| @objc func storeContentOffsets(for tableView: UITableView, dataSource: RecentsDataSource) { | ||
| reset() | ||
| let sections = sectionWithTypes(for: tableView, dataSource: dataSource) | ||
|
|
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| for (section, sectionType) in sections { | ||
|
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| let indexPath = IndexPath(row: 0, section: section) | ||
| guard let cell = tableView.cellForRow(at: indexPath) as? TableViewCellWithCollectionView else { | ||
| continue | ||
| } | ||
|
|
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| contentOffsets[sectionType] = cell.collectionView.contentOffset | ||
| } | ||
| } | ||
|
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| @objc func restoreContentOffsets(for tableView: UITableView, dataSource: RecentsDataSource) { | ||
| let sections = sectionWithTypes(for: tableView, dataSource: dataSource) | ||
|
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| for (section, sectionType) in sections { | ||
|
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| let indexPath = IndexPath(row: 0, section: section) | ||
| guard | ||
| let offset = contentOffsets[sectionType], | ||
| let cell = tableView.cellForRow(at: indexPath) as? TableViewCellWithCollectionView | ||
| else { | ||
| continue | ||
| } | ||
|
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| cell.collectionView.contentOffset = offset | ||
| } | ||
| reset() | ||
| } | ||
|
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| private func reset() { | ||
| contentOffsets = [:] | ||
| } | ||
|
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| private func sectionWithTypes(for tableView: UITableView, dataSource: RecentsDataSource) -> [(Int, RecentsDataSourceSectionType)] { | ||
| // We associate the arbitrary integer index of a section at any particular time with its semantic value (e.g. 2 = `favorites`). | ||
| // At this point the index could equal -1 because not all indexes in data source ara valid for every screen | ||
| return [ | ||
| (dataSource.crossSigningBannerSection, .crossSigningBanner), | ||
| (dataSource.secureBackupBannerSection, .secureBackupBanner), | ||
| (dataSource.directorySection, .directory), | ||
| (dataSource.invitesSection, .invites), | ||
| (dataSource.favoritesSection, .favorites), | ||
| (dataSource.peopleSection, .people), | ||
| (dataSource.conversationSection, .conversation), | ||
| (dataSource.lowPrioritySection, .lowPriority), | ||
| (dataSource.serverNoticeSection, .serverNotice), | ||
| (dataSource.suggestedRoomsSection, .suggestedRooms) | ||
| ].filter { (section, sectionType) in | ||
|
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| // We only want indexes that are valid for a given view and actually shown on the table view | ||
| section != DATA_SOURCE_INVALID_SECTION | ||
| && section < tableView.numberOfSections | ||
| } | ||
| } | ||
| } |
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| Original file line number | Diff line number | Diff line change |
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| @@ -0,0 +1 @@ | ||
| Rooms: Remember offset of collection views during table view reload to avoid jitter |